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Diagnosing Aircon Problems

Hi Brian,
Excellent detail and just what I was after So +2 from me :D
My aircon does not work; I have got to the point where I connect the battery +ve to the compressor clutch relay socket to make the clutch engage. I see a slight sparking at the battery terminal as I connect the wire but do not get a click noise from the clutch area. From your electrical diagram this terminal on the relay base goes direct to the electromagnetic clutch coil on the compressor. Since I am getting some arcing at the battery terminal when I dab the wire on then there is a load present. I am now ***uming that the coil is working and that the clutch is seized off. I can turn the inner part of the clutch pulley when I have this cable connected or not. I have just tried again and can actually feel this inner hub slightly deflect when I connect the cable but no positive click noise or gripping of this hub. My next step is to try and examine this clutch. Since there is gas pressure I don't want to get it evacuated unless I have to, I also want to be able to drive the car. Is there a guide on how to remove the compressor, check the clutch etc or any advice would be appreciated?

Jay
 
Hi Jay

To be 100% certain of whether you do or don't need to remove the compressor to do any further work, try the step where I say "check if you have enough gas" etc. I should really have put that step in differently in the DIY.

In other words, try doing it with the engine running. Just connect the terminal in the relay base to the battery positive and look to see if the inner hub on the compressor starts to spin. If it does not start to spin, then the compressor clutch is definitely seized off. You don't need to leave the wire on battery positive for long, just do it a few times with the engine running and look to see if the inner hub starts to spin. don't leave the wire like this for more than 30 seconds in total.

If it doesn't start to spin (especially if you get a bit of sparking) then yes you will need to remove the compressor and strip it down.

Let us know how you get on

All the best, Brian
 
just to let you know ive had my pressure sensor changed on my ctdi today and my air con now works again :D
 
Hi Brian,

I just tried as you said and unfortunately it does not spin or even try to. I am sure it is seized off. Are there any ***embly drawings or DIY instructions for fixing the clutch? If it is just seized off does that mean I can just swing it low enough to get to the clutch and free it up WD40 style ( ***uming nothing is actually broken), or are we talking strip right out and replacing parts?

Jay
 
Hi Jay

***embly drawings are here. This is on a dealer's web site (Lings Honda). If you want to find drawings for your own car at any time start here.

I don't know if you can free it with WD40, whatever you do it will be easier to get at if you remove the bottom engine cover (a few clips and screws, but the cover also wraps up the sides where there are more clips, you can see the lower cover on the left here).

To remove the compressor you will have to have the gas evacuated as you say.You will have to remove the auxiliary belt, so you won't be able to use the car with the compressor out :(

cheers, Brian

.
 
Hi Brian,

Thank you for links, very much appreciated. After my last post I had to go check if WD40 would work. I removed front wheel and the inner cover. I found I could push the inner ring inwards about 2mm till it met the pulley, then released it and it sprung out again. I then did the relay base to +ve trick whilst my hand was down on the pulley. I connected the +ve and pressed the inner ring and it snapped shut. I disconnected the power and reconnected several times and the clutch went in and out fine. Then put relay back in and started car, turned aircon on.....nothing happened. I started to pull relay out and I could feel it clicking so pushed relay back in. I 'carefully' tapped the clutch plate and it snapped shut and started spinning the compressor.

Nothing went cold even though I set temperature to low. I thought I felt the one pipe from the compressor slightly cool but then nothing. This is the Tourer Diesel so the sight glass in the refrig line is visible from above. I saw what appeared to be 6 or 7 bubbles or droplets of refrigerant go past from left to right (towards compressor) in the first 20 seconds, then no more. This may now point to low refrigerant however I would have thought that the clutch wouldn't come in if it was so low as not to work..... Does clutch only engage when the system is happy IE refrigerant is neither high or low pressure and temperature being called for is lower than ambient?

I know I have to deal with the lazy clutch (I suspect a weak coil.....Just had a thought, I wonder if tthere is a high resistant joint to the coil!!!! will have to check that one) but want to establish this other issue first.

I will now read up on your links.


This is very much appreciated
Thank you
Jay
 
Hi Jay

I'm impressed with the idea of tapping the clutch plate through the side panel while the engine is running :D

On the system in the petrol car, there is no low pressure sensor, so I would expect the compressor to run on the system in the petrol car even when there is low or no gas.

On the diesel, I don't know when the low pressure sensor will switch, it may even switch at negative pressure rather than low pressure. I think negative pressure can occur when the aircon is running in very low temperatures and high humidity, when one might use the aircon set to Lo to try to demist. In this situation, the pipes can frost up, and then low pressure (negative pressure ?) will cause the valve next to the condesner to be switched. But as I say, I'm not certain of this. But anyway, the point is, if you heard the relay clicking, and the clutch stayed in when you tapped the plate with the engine running, this does suggest (1) lazy clutch solenoid as you say (2) low gas pressure if there's not much cold air blowing out on Lo .... I ***ume that the condenser is in good condition i.e. not very badly perished, take a look through the bottom grill.

Have you had the system pressure tested ? Halfords or somewhere usually charge £10 or something like that to pressure test.

If you have a DVM, check the current to the compressor clutch, should be 3 amps.

cheers, Brian
 
Hi Brian,

I've just gone out and checked the current. With car not running and just energising the coil I get 3.6A. Funny thing happened, the clutch didn't pop in on the first few power cycles until I pushed it in and now it goes in all the time. When it was popping in and out previously it was moving a good 2mm, now it doesn't seem to pop back out as far. Almost as if it was going out too far before and the coils magnetic field couldn't quite reach it if you get what I mean. Anyway I will investigate that farther at some point.

I had a look at the condenser :eek: how exposed. It has some debris blocking and some of the fine fins have gone, besides I did get a spurt out of the valve when I checked so ***ume it's not blown yet.

I just had a look on Halfords www and they are now doing FREE pressure checks on the air con (a local one for me too...actually pass it most days to and from work). They do a regas but I will have to ask what they actually do as it sounds like they do it on pressure and not weight. What advice would you give on this point? I will get pressure checked out after work tomorrow.

BTW as for the tapping of the clutch...it was calculated in that I made sure no screw heads were protruding that could catch and the angle of the knocking stick ensured it should of bounced away in a safe direction....as I said calculated :blush: . To anyone else reading this part I would not recommend touching anything moving on a car engine.

Thanks
Jay
 
You've done really well there Jay, saved yourself a fortune at a dealer LOL.

Not sure of the way Halfords do the pressure check, but it sounds to me that if they say pressure is ok, then you need to change your condenser (which needs doing even if pressure is low)

If the compressor is pulling in now, take it for a drive on a dual carriageway or motorway at 60-70 mph in cool air, with aircon on Lo. If it blows cold, then it's the condenser which is the main problem i.e. gas probably ok ....and also a problem with the compressor clutch, which you've fixed for the time being (not related to gas pressure etc etc).

PS .... I did the condenser on my car myself, but I didn't take any pics. It's best to remove the front bumper. But, I will be replacing one of my front fog lights very soon, so I'll take some pics and write up (1) how to remove front bumper (2) how to change condenser

.
 
Update*

I popped into Halfords autocentre yesterday to get a FREE pressure test. The guy said what they do is evacuate your system first and then charge it with the correct amount of refrigerant. They then check for leaks around all joints etc. by trying to detect for a special dye within the refrigerant. If they find a leak they will evacuate the system again and tell you where the leak is. He said then I can go away without paying. If the system passes the test then it's £49.
They said they needed an hour to do the work without booking, since it was near the end of the day I wanted to wait and see if you all thought this was a fair deal.
 
hmm not sure if I'd call that a pressure test, it's a leak test.

All they need to do is plug in their pressure gauge onto the "Low" blue fill point, and tell you what the reading is.

They used to charge £10 to do this, or buy one and do it yourself for £20, or look on ebay of course. Or just go for a drive when your compressor is working, with aircon set to Lo in cool air at 70 mph, and see if cold air blows out

IMO that's all you need at this moment in time, because you may later need to remove the condenser and/or compressor anyway.
 
Hi Brian,

I've been for a cruise and could only feel the ambient air coming in however I could not be sure the clutch was in (will check under the hood tomorrow to ensure it is and then go for a cruise). I have also ordered a new condenser, once it arrives I will get the system evacuated. Then I can strip out the clutch to see what's occuring in there too (from the drawings it appears a very basic setup so maybe just a circlip groove worn or something).

Thanks
JAy
 
Hi Jay

Matt (mattlee) got a new condenser for the diesel car for £88. See his link to the website in here.

cheers, Brian

PS: condenser for the petrol car can be bought from Unipart for £70 (well that's how much I paid a year ago).


That's a good site that Matt found, here is the main Honda list

.
 
Hi Brian,

I bought the condenser for £120 delivered with 2yr warranty. That price is very good....plus VAT mind, so I don't feel so bad now lol. The links are in my favorites now thanks.

I couldn't get my clutch to consistantly pull in so will wait till I fit the condenser and fix it then...try too. I will take some pics of my findings for everyones reference. It may be a few weeks away as I have a busy few weeks ahead, as well as hoping to do an oil change next week.

I will let you know how it goes.

Jay
 
Update,

Been very busy... fishing trip etc.

I have solved the clutch actuation reliability issue today.
Engine is OFF and key removed for this task.
1) Remove front off side wheel (Jack, axle stand) and remove the 2 trim clips that hold part of the under tray to the wheel area. You can then easily flex this flap of trim away to gain access to the compressor (there is no need to remove the wheel arch cover for this job).
2) Remove the clutch relay and force 12v onto the coil as described previously (I crimped a blue male spade end onto one end of a piece of 1mm2 cable so that it fitted securely in the relay base). I was then able to tap the clutch to make it snap closed.
3) Now that the clutch is engaged and the drive belt is still in place to hold everything still you can undo and remove the 6mm screw from the centre of the clutch with a 10mm spanner.
4) De-energise the coil by removing the wire.
5) Carefully withdraw the clutch plate by simply sliding it out. You will notice the spindle is splined and ***uming it is untouched you will find 3 washers behind the clutch. (I had 2 washers that appear to be identical thickness and one slightly thicker, if it is of any use I can measure the thicknesses). At first I thought someone had been here before because it is very unusual to find several washers in the same place after all if you were machining to precision you would make one thick washer and not stack several together. After looking at Lings drawing My link I can see that this is normal. So the question is 'why?' well I would guess that this is intentional to allow you to adjust the gap between the clutch and pulley face. (anyone know different?)
6) Without my vernier callipers and micrometers with me (at work) I had to guess and removed one of the smaller washers. Then refit and tighten up the clutch to check (re-energise the coil to allow you to tighten the 6mm screw tightly)
7) Remove the cable to de-energise the coil one more time. This will allow you to check that the clutch is NOT rubbing against the pulley face as this is now in the disengaged mode. (if it rubs then it will wear the clutch friction surface faster and may actually damage it ((a bit like riding your drive clutch)) I actually cycled the power to the coil a few times with my hand on the coil to make sure it was physically moving and leaving a gap. I ***ume there is a min/max tollerence on this gap (any ideas?)
8) Refit the trim and clips, replace wheel etc.

The clutch now reliably engages every time.

I don't know if this is by design, unless Honda are rubbish at engineering then I would say that the 3 washers are to allow you to adjust the clutch surface gap as the clutch wears. Seems bit crude but it certainly worked for me.

I didn't think it necessary to take photos however if you want some I can take them at the weekend (only take 20 mins to strip again)

Now to get the system evacuated so I can fit the condenser... Any tips on removal/refitting?

Jay
 
That's a pretty impressive bit of DIY there, saves a lot of £££££ to get the compressor working again.

I also like your idea of using a male spade terminal to plug the wire into the relay base.

When I replaced my condenser I found it straightforward once I'd removed the front bumper. There are two brackets at the top of the condenser holding it in place, then undo the pipes (gas removed of course or it will blast in your face). I also had to remove the brackets on the top of the engine radiator to move it inwards at the top a bit, giving me enough room to pull the condenser out. As far as I remember, that was about it.

You should have it ready for our belated summer that they reckon will start next week LOL
 
Yeah, those washers are intended to adjust the AC clutch. I saw it somewhere in the repair manual of the 6th gen Accord. Latter I can tell you more about this, including the recommended tolerances by Honda, at least for the 6th gen, which must not be very different from the 7th gen.
 
Brian,

Did I miss something with this summer report you claim. At first I thought you had heat stroke lol

I will attempt the condenser transplant this weekend hopefully. From what you mention it should be fairly simple :unsure:


Pedro,

I would be interested in any info on these washers. It's been bugging me all day because I can't quite make sense of it. At first I thought it made some sense as in my previous post. However if the washers are to compensate for clutch wear then all they do is reduce the gap when the aircon is in the off condition and reduce the flex that the spring plate moves due to reduced travel. The reason I removed a washer was to move the plate closer to the electro magnet so it would pull the plate in. If my thinking is correct then the plate should have moved in originally because if the clutch plate wears it will not move the metal back part (the bit attracted by the electro magnet) further away, it should remain in the same position IE as the friction material wears it only increases the distance this non magnetic surface is from the pulley and nothing else.

It may be that the electro magnet is weak on my unit and that I am just lucky that the clutch is worn enough that I can bring it all closer in.

Thoughts?

Jay
 
What I understand is that over time, the clutch gets worn, which creates a larger gap between the pressure plate and the pulley, thus the use of shims to compensate the worn material. Also, Honda sells sets of shims, so they must have a significant purpose.

Here is the info about the Denso compressor for the 6th gen:
http://www.sendspace.com/file/nufvdv

And the info on the Sanden compressor for the 6th gen:
http://www.sendspace.com/file/5b7bz3

For the Denso compressor these are the values that must be seen:
Clearance: 0.45 +0.15, -0.10 mm (0.018 +0.006, -0.004 in)

And for the Sanden compressor:
Clearance: 0.5 + 0.15 mm (0.020 0.006 in)

Actually I think mine is with a gap too large, I haven't measure yet, but by the the looks of it, its about 1.0mm... The problem is that it's not easy to reach the clutch without removing the compressor, which is not viable, since I don't want to loos all the gas in the system...
 
Thanks for the pics Pedro,

I notice they say 'shim' which indicates it is adjustable. Strange how on the 6th gen they are available in .1, .3 & .5mm yet the ones on the 7th (mine anyway) are way thicker, more like .5 & 1mm ish ( I will now have to go measure them at the weekend wont I????, as well as the clearance.

At least my clutch is now working consistently and I have a better understanding (sometimes I wish I was there when these ideas pop up in the designers heads).

I don't think any of this will answer my question of why I had to remove a shim to get the electro magnet to pull the clutch in but at least I have a better understanding of how it works and that the clearances are important.

Jay
 
Some really useful chat on the compressor. If/when I start to get problems with my compressor those pdf's from Pedro will come in handy.

Jay, here is an interesting weather video on BBC, how meteorologists expect the jet stream to move back to where it would normally be at this time of year. Normally low pressure systems should be NW of UK, with high pressure systems over the UK. The Gulf Stream and the Jet Stream both influence our climate. There's a hypothesis that long-term the Gulf Stream may move south, resulting in harsher winters in the UK.
 
Jason, if you remove the clutch again, take some pictures of it B)
 
Brian,

That is not a bad explanations of how the jet stream works. Thanks. I May eventually never need air con again soon then lol.


Pedro,

I have just opened a photo bucket account so intend to do the pictures on Saturday before I start the condenser transplant. Then work out how to post them on here hmmm

Jay
 
Update

I popped into Halfords on the way home today and purchased an EZ-chill gauge ***embly (same as you mentioned previously) just to see if it was residual pressure or not in the system before commencing work on this condenser transplant tomorrow. The pressure on the Low pressure side was 45psi (after a 4 mile drive with engine up to working temperature), according to the literature with the gauge that is at the top end of the filled pressure scale. I ***ume this means that there in theory is enough refrigerant in the system (gas anyway). On one hand at least I know there are no leaks but on the other it does not explain why the system is not functioning. Even with some cooling fins on the condenser missing I would have expected some temperature drop but am detecting nothing at all on the pipes. I again saw one or 2 bubbles pass the sight glass.

1) aircon set to LOW and blower on 3
2) Clutch engaged
3) Both condenser and engine fans were on
4) car had been running for 4 miles plus stop at Halfords then further 15 mins on drive

Even when driving at speed I get no temperature drop. I would guess that there is no flow of refrigerant.

Q
1) Should I see a pressure fluctuation between compressor running and not running? If I engage and disengage the clutch via air con on/off on dash (and physically checking clutch) I get a constant 45psi on the low port. I was expecting to see a change but it seems stable as a rock.
2) Where does the signal come from for the valve and what determines when it should energise (one below the pressure switch on the condenser). I will electrically check that power is present first thing in the morning.

Without knowing any more at the moment things are suggesting either a blockage, compressor not pumping or this valve not operating.

Jay
 
Hi Jay, that was a very wise decision to buy that aircon pressure gauge from Halfords.

If I understand correctly, then I agree that either the compressor is not compressing, or the valve in front of the condenser is not opening. To be sure which, a bit more logic (to any reader, first make sure your compressor clutch works, that your relay works, and that you have gas in the system, as Jay did above) ......

1) go into the A/C manual control display
2) on the display, set A/C On
3) set the air direction to ----> (direction not critical but this way you can feel the air blowing straight out of the midddle)
4) set fans to max (again not critical but again you can feel the air blowing out, plus more likely to "stress" the system)
5) use the blue (cold) button (next to the Auto button) to set the top console display to Lo
6) get out and watch the compressor. If it is running then the system has turned it on. If the compressor then stops and never starts again, then the compressor has pressurised the high side of the piping, and the high pressure part of the dual pressure switch has indicated to the system to turn the compressor off (note to any reader, diesel car has dual high and low pressure switch, petrol car has single high pressure switch only) ....... i.e. if your compressor runs and then stops and doesn't come on again, then your aircon valve has not opened. The compressor may come on again after a very long delay, but normally when everything set up as above, the compressor should cycle on-off-on quite often
7) If the compressor never stops, then it is not compressing. Go into the A/C display, and set A/C Off , the compressor should now not be running because the system has switched it off. Check that you can turn the compressr on and off using the On and Off on the display.

Summary: with temperature set to Lo, if you have sufficient gas on the Low feed to the compressor, and if you can turn the compressor on and off with the manual display, and if the compressor never stops with display set to On , then the compressor is not compressing.

EDIT: I see that the single high pressure switch on the petrol car is AFTER the condenser. The summary above ***umes that the system on the diesel car works in the same basic way as the system on the petrol car.
However, on on the diesel car the dual pressure switch is BEFORE the condenser, and also, the valve is immediately after the dual pressure switch (and also before the condenser). My understanding is that the valve is operationally ***ociated with the low pressure part of the dual pressure switch on the diesel car, but as stated previously, the diesel car drawings for the heater unit (behind the dash) seem ambiguous. So without being sure of the operational purpose of the valve between dual pressure switch and condenser, there is a possibility that if the valve is stuck open then the system may not work.

So on the diesel car, if the system fails as in my Summary above, I cannot think of a way to test if the compressor is not compressing, or if the valve is stuck open. My guess would still be the former, not the latter, but you would need to de-gas the system to take either out to check.
.
 
Hi Brian,

The plot thickens.

I double checked the settings;
1) Manual control set to ON
2) Temp LO
3) Fan on FULL and blowing out of top centre grills only
4) Clutch is in and compressor shaft is rotating.
5) Pressure gauge still shows 45psi (even before I started car this morning)
No bubbles in sight glass and no temp change or pressure change.

I decided to try and check this valve (the one mounted below the hi/low pressure switch
My link
Because it is quite awkward to get your test leads through the bumper opening and see what you are doing, unclip the socket from the condenser frame
My link

I measured a pd of 14.4v on the plugs top pin to earth but not between the pins. I ***ume the bottom pin should be 0v but not sure if it should be a switched 0v or a constant one. I could not get any continuity (in fact open circuit) between this bottom pin and earth.
What I did was connect both coil wires direct to the battery, I could hear a positive click each time. Normally with direct coupled coils to valves (not pilot operated) when you hear a positive click the valve itself is opening and closing, although this does not guarantee it is sealing completely. I also measured the current and got .85A
My link
To make sure the valve was open I kept it directly linked and turned on the air con as before. Again no pressure dip or bubbles in the sight glass (I cycled this valve several times and although I could hear the click I had no results).

Incidentally the 12v supply to the coil energises when you turn the key (appears to be on all the time after this) and once the car starts it raises to 14.4v which suggests it's a permanent supply and not regulated through any electronics other than the voltage regulator on the alternator. No matter what I did I could not get the 0v to appear (open circuit).

Q
1) Where does this +ve feed originate from
2) Where does the 0v originate from? IE if it is meant to be grounded then where?
3) Does anyone have a wiring diagram?
4) Should I see bubbles or visually see liquid moving in the sight glass when the valve is open and the compressor is on? The sight glass on our ammonia freezers at work is vertically mounted and you can see the level of liquid ammonia but because the car one is mounted horizontally I would ***ume you will just see bubbles?????
5) Is the valve opened when energised?

Thoughts in my head
It may be possible that because the condenser is on rubber mounts an earth is supplied via the cable
It may also be possible that the 0v is meant to be switched and not the +ve
Caffeine needed (already been through 5 mugs
I know I will need to go get the system drained to transplant this condenser but don't want to do that until I have concluded the above (I believe the condenser swap will only improve performance and not just be the difference between working or not).


Jay
 
Pedro,

Pics on how to adjust the compressor clutch clearance;

1) First engine off, key out of the ignition, handbrake on, wheel chocks under the rear wheels, jack up the car and ALWAYS support on axle stands & remove wheel. Note: where the trolley jack is placed, there is a convenient gap in the under tray for this (there is also a 10mm gap between trolley jack and car to be sure the weight is on the axle stands.
My link
2) Remove the 2 trim clips from the inner cover
My link
3) No need to remove the cover as you can carefully flex it away without damaging it to expose the clutch
My link
4) Measure the clutch clearance (I hadn't done this initially but it was 153 thou (make a note of this).
5) Now put power onto the electromagnetic coil so that the clutch stays rigid to allow removal of the M6 screw. Either use a second person to do this or use a crocodile clip to hold the wire onto the +ve terminal.
My link
My link
6) loosen and withdraw the screw
My link
7) Remove power from the electromagnetic coil and withdraw the clutch being careful not to lose the washers....I mean shims :D Note there was some residual magnetism holding the washers (I didn't glue them there :p)
My link
8) Here is a pic of the clutch plate
My link
9) I originally had 3 washers (shims) in mine which according to the Honda drawings is standard. The dimensions were 46 thou (1.17mm), 40 thou (1.02mm) & 67 thou (1.72mm) (In a previous post I guessed .5mm on the one I removed, I was way off but now have had my eyes recalibrated :p. I removed the 46 thou shim to reduce the clearance.
10) Reassemble in the reverse sequence. Finally check the clearance before you put the trim panel back in place. I measured 10 thou.
My link

Pedro you gave these details of the clearances

For the Denso compressor these are the values that must be seen:
Clearance: 0.45 +0.15, -0.10 mm (0.018 +0.006, -0.004 in)

And for the Sanden compressor:
Clearance: 0.5 + 0.15 mm (0.020 0.006 in)


Does this mean Denso clearance should be between 0.35 and 0.60 (14 thou and 24 thou)?
Normally tolerances are written like this
My link

***uming the 6th Gen clearance for the Denso is similar then I may need to swap some shims around. With what I have I can achieve 10 thou (now), 16 thou, or 56 thou (original). At the moment there is no hint of heat/rubbing so will leave be for the moment as it is working.

Jay
 
Jason, great wright-up on this. I might do this a try now that I know what to expect, and check the clearance of the clutch, although my AC apparently seems to be working ok.

About the clearances, I guess you are right, and that info was taken from the Honda workshop manual, so it must be correct.

I have just remembered that I also have some info on the Acura TSX, equivalent to the Europen Accord 2.4. Although not the same as yours not the same engine, and apparently the AC system of the petrol and diesel models are different, the compressors might be the same.

For the Acura TSX, the correct clearance are the following:
Clearance: 0.5 +/- 0.15 mm (0.020 +/- 0.006 in.)

You can get the info on the Climate Control System of the TSX here, it might be useful: http://www.sendspace.com/file/ob34r1
 
Pedro, that document on the TSX Climate Control System is fantastic !!

Unfortunately for Jay, it's the same as the system in the Accord Petrol, not the Accord Diesel.

In order to answer Jay's latest questions I need to describe how the aircon works. I have taken a couple of screenshots from Pedro's document and used them to describe the way the system works on the Accord Petrol. After that I will describe how I think the system on the Accord Diesel works .... NOTE: I have the Accord Petrol !!


Climate Control System on the Accord Petrol

Refer to this diagram (from Pedro's document)
0023.jpg



The entry pipe to the compressor contains vapour at relatively low pressure.
When the compressor is running, the exit from the compressor and entry to the condenser contains vapour at high pressure.
When the compressor is running, the vapour loses heat in the condenser, and so the vapour has condensed into high pressure liquid when it leaves the condenser.
The expansion valve before the evaporator meters the high pressure liquid to a lower pressure, and as this passes through the evaporator it gains heat (making the evaporator surface cold) and becomes vapour again at relatively low pressure.

The diagram above tends to imply that the pressure switch will switch at high and low pressure, but IMO it is only a high pressure switch on the petrol car. This seems to be borne out in the circuit diagram below (also from Pedro's document)

0024.jpg


In the circuit diagram, there is a thermal protector in series with the pressure switch. This thermal protector is inside the compressor, and this protects the compressor from over-running condtions when there is not enough gas in the system.



Climate Control System on the Accord Diesel
IMO the main operation of the system is the same, but as I have pointed out, the Honda drawings on the Lings website are IMO ambiguous for the diesel car.

If I am correct that the operation of the sytem is essentially the same, then why the mods for the diesel car ?

Well IMO it's nothing to do with the fact it's diesel, I suspect that it's simply because the diesel car in the UK is to the same spec as in Scandinavia (so by impication the petrol car in Scandinavia would have the same system as in the diesel).

The problem in Scandinavia is that the piping in the engine compartment could freeze, indicated to the system as low pressure at entry to the condenser when the system is running the compressor. The system would then close the valve to increase the pressure coming out of the compressor, and when the high pressure switch opens, the system would stop the compressor and open the valve. There would be a timer in the control system to stop the system from cycling too rapidly. This is known as "defrost pump down".

The Sight Glass
when the system is running properly, liquid can be seen in the sight glass. On my car, this is visible as green liquid (with some bubbles). When the compressor is not running, the sight glass is dark (no liquid).

The wiring to the valve on the Diesel Car
From Jay's excellent work previously, I would expect that 0V is switched to the valve by the system. I would now think that the valve is normally open, and the system switches 0V to close the valve. However, we need someone to make sure of this by measuring the connector as Jay did, on a diesel car that is working properly !!

My conclusion Jay, is that your compressor is not compressing, but I am only 90% certain of this LOL

EDIT normally there would be a heater coil somewhere between evaporator and compressor which would be activated during defrost pump down, but there doesn't seem to be any evidence for this on the diesel, so it might not be a defrost pump down system. Maybe the system is simply modified to sense low pressure as in the first diagram, but if so, it begs the question as to why the pressure sensors are before the condenser, and why there is a valve there too.

But I can only suspect that Jay's compressor is not internally rotating even though the clutch is pulling in.
 
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