aircon help, please
Discussion
The perennial problem. Having just had my aircon system tested and regassed as part of the trouble-shooting process (all OK), I have the following symptoms. When I press the dashboard switch, the light and fans come on (footwell relay ok) but the compressor does not. Give the compressor a direct 12v and it runs fine. The garage suggest one or more of the pressure sensors has failed. I have disconnected them both and measured the resistance, both give basically open circuit, so either they have both failed or it is something else. My first questions are: have I checked in the right place for the pressure sensors? (pictures attached) and is open circuit what they should show when tested?
If they are the problem, where can I get replacements and can they be replaced without disturbing the gas?
If they are not, is there another relay I should be looking for?
Thanks
If they are the problem, where can I get replacements and can they be replaced without disturbing the gas?
If they are not, is there another relay I should be looking for?
Thanks
StreetDragster said:
If they are a pressure switch, rather than a sensor, could you just bridge the contacts for testing to see if the system operators, and then alternate to find the trouble sensor?
Matt
Thanks, that is an idea I had, but thought I would wait for an expert to let me know it is safe to do so. I don't want to blow anything by shorting them, I was wondering whether it needs a specific resistance.Matt
there's an ac relay as well that drives the compressor clutch, so it could be that. Relay 1 in the engine bay?
or fuse 3 of the rear 4 way box?
The stats: 1 should be open and close when the fluid gets hot to turn the fans on.
There's a second stat that has to be closed for the compressor to run but I can't work out where this physically is.
I think you've got pics of the 1st stat, and a low pressure switch.
The second stat is maybe on the compressor as an overtemp cutout? or in the cabin as an under temp cutout??
or fuse 3 of the rear 4 way box?
The stats: 1 should be open and close when the fluid gets hot to turn the fans on.
There's a second stat that has to be closed for the compressor to run but I can't work out where this physically is.
I think you've got pics of the 1st stat, and a low pressure switch.
The second stat is maybe on the compressor as an overtemp cutout? or in the cabin as an under temp cutout??
Edited by Green3R on Thursday 27th February 14:12
Green3R said:
there's an ac relay as well that drives the compressor clutch, so it could be that. Relay 1 in the engine bay?
or fuse 3 of the rear 4 way box?
The stats: 1 should be open and close when the fluid gets hot to turn the fans on.
There's a second stat that has to be closed for the compressor to run but I can't work out where this physically is.
fuse 3 is fine but I would appreciate further directions to the second stat and relay. Presumably it's wheels off and more to get close?or fuse 3 of the rear 4 way box?
The stats: 1 should be open and close when the fluid gets hot to turn the fans on.
There's a second stat that has to be closed for the compressor to run but I can't work out where this physically is.
Edited by Green3R on Thursday 27th February 14:12
I've just printed off the circuit diagram and there seem to be at least six relays involved. Relays D,H,F & N and fuses 11 & 12 are in the footwell and I should be able to find relay fp01 (presumably the relay 1 you mention in the engine bay) as it is is linked to fuse 3 on the bulkhead.
Does anyone know where relay O is though? Looking at the wiring, it looks as though it could be near the compressor but the diagram also makes it look as though it could be in the footwell linked to relays F & N.
Does anyone know where relay O is though? Looking at the wiring, it looks as though it could be near the compressor but the diagram also makes it look as though it could be in the footwell linked to relays F & N.
Edited by dave sutton on Thursday 27th February 18:58
I had a problem getting my aircon to run properly so I took it to be checked by a specialist. He said there should be a thermostat somewhere that stops the air box freezing and that it could be faulty. I eventually found it in the footwell by the fusebox, it was wrapped in black foam with two purple wires going to it. I have bypassed it for now (connected the two wires together, simples) and the aircon is working great! It's worth trying as yours could be faulty also.
If any of you boys that have gone without aircon have one of these thermostats sitting around I'll be happy to buy one from you?
If any of you boys that have gone without aircon have one of these thermostats sitting around I'll be happy to buy one from you?
Right. I pretty sure I have tested, cleaned and reseated every fuse and relay mentioned in the manual, both in the footwell and engine bulkhead. So, I am left with the original suspects and thermostats. Also, I didn't find anything in the footwell with purple wires so maybe that is something later models have my 02 2.5 doesn't have?
On the other hand, my garage is pretty cold and it is hard to tell whether the air blowing with the aircon on is any colder than when it is off. Could it be that it is so cold in there that the aircon is quite simply not kicking in even if my fiddling has fixed anything. Maybe I'll wait for some warmer weather before continuing.
On the other hand, my garage is pretty cold and it is hard to tell whether the air blowing with the aircon on is any colder than when it is off. Could it be that it is so cold in there that the aircon is quite simply not kicking in even if my fiddling has fixed anything. Maybe I'll wait for some warmer weather before continuing.
I'd now be betting on it being the 'footwell' stat. If this is to stop the airbox iceing, I'd guess that it would normally be stuck to or in the airbox so have a good search around. Maybe the one that's in the footwell had dropped off where it's supposed to be?
Doubt it's too cold for it to work though so I think you'd hear the clutch drop in and out if it were working.
Doubt it's too cold for it to work though so I think you'd hear the clutch drop in and out if it were working.
Green3R said:
I'd now be betting on it being the 'footwell' stat. If this is to stop the airbox iceing, I'd guess that it would normally be stuck to or in the airbox so have a good search around. Maybe the one that's in the footwell had dropped off where it's supposed to be?
Doubt it's too cold for it to work though so I think you'd hear the clutch drop in and out if it were working.
its stuck to the side of the air box close to were there evaporator pipes go in... its a wire coil that is then inserted in the evaporator to sense when its over freezing Doubt it's too cold for it to work though so I think you'd hear the clutch drop in and out if it were working.
If I turn the aircon on with the ignition running, I hear the fans start up but no sound which might be the clutch activating. Will it operate if the engine is not running?
Will the air box thermostat be visible from the footwell, or do I need to look from outside in the front nearside?
Will the air box thermostat be visible from the footwell, or do I need to look from outside in the front nearside?
dave sutton said:
If I turn the aircon on with the ignition running, I hear the fans start up but no sound which might be the clutch activating. Will it operate if the engine is not running?
Will the air box thermostat be visible from the footwell, or do I need to look from outside in the front nearside?
Yes, you should hear the clutch click in and out as you switch it on and off on the dash switch. Will the air box thermostat be visible from the footwell, or do I need to look from outside in the front nearside?
wessexrfc said:
Yes, you should hear the clutch click in and out as you switch it on and off on the dash switch.
thanks, I definitely hear nothing like that so it's carry on looking then.I need to get on with other stuff for a few days. I'm not going to let it beat me/us, when I get back to it, I expect I'll be back with more questions. Thanks everybody very much for your help so far.
It still sounds like it could be your stat, mine was the same as yours and it was driving me crazy as I couldn't work out why it wasn't coming on. You need to lay on your back with your head in the passenger footwell and look above the fuse box, it will have two purple wires and a coil going to it. You should have 12v going into one side of the stat, and 12v coming out if it's working ok.
wessexrfc said:
Could be the stat, strange the fans are cutting in unless its after a run and the cars warm, do the fans cut in when the cars cold?
Yes, from cold, with the ignition on but not the engine running, pressing the dashboard switch brings on the little green light and the fans start up, but no sound from the bulkhead.I'm still suspicious of the sensors on the high and low side that I mentioned in my first post. With them both showing infinite resistance surely that is no different from being disconnected?
When I get back, I'm going to do some more investigation with the multi-meter and possibly try connecting low wattage bulbs across them to see what happens.
I'll also peer a little further into the footwell.
Edited by dave sutton on Saturday 1st March 14:17
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