P38 diesel Air Con problem

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Charles Banbury

Charles Banbury

Active Member
Posts
114
Location
Oxfordshire
Happy Easter. I have just returned from having my air con re-gassed. As per the details below, the gas remained in the system and there are no leaks. However, the aircon still fails to operate. I know that when the light is on, it is off and when the light is off, it is on. Mad. When I press the AC button there is a change noticeable on the rev counter but no cool air. I have tried to find the compressor. That was easy on my old 4.6 but with the diesel where is it? Also, when I press the Auto button all that seems to happen is a drop in
the fan speed. Any advice chaps? Many thanks .
IMG_2649.JPG
 
Compressor is drivers side, in front of turbo and down a bit, get underneath, remove the engine cover and follow the smaller drive belt.:) Where did you take it to ? Kwik**** and ATS weren't charging after a refill if you didn't get cold air coming out.
 
Luckily I went to Quick F so there was no charge. The HEVAC has the 'book' symbol. Does this mean that the system will not operate even if the compressor is OK?
 
Not sure, check the connections to the switches ( dual pressure switch and single pressure switch), mine had a dirty connection that prevented the system from operating. They are passenger side bottom of the radiator, engine side,will see them attached to the pipework. See section 82 on Rave
 
Get them to check the pressure on Hi and Low sides.
The figures should stay somthing like,
Hi - 150 to 200 PSI
Low - 25 to 30 PSI.
As mentioned could be pressure switch related. Check whether both fans are working with AC on.
 
Thanks everybody. I have had a look for the pressure switch but think that I need a few more clues to find it! I have also had a look on RAVE, my first look and cant find section 82. Feel rather like the stupid kid at school who is constantly harassing the teacher! Is this right?
upload_2016-3-27_11-59-32.png
 
On the diesel the pressure switch is on the pipe work by the dryer behind the bumper passenger side , on the autos its not so easy to see as its in front and above the gearbox oil cooler rad behind the fog light grill, hope that makes sense
 
Yes they are the ones, If I am right they work on a ground feed you can pull the connectors of and bridge with a link to bypass to work,
but only two connections at a time on the tri switch, Wammers would know more.
 
brianp38dse said:
Yes they are the ones, If I am right they work on a ground feed you can pull the connectors of and bridge with a link to bypass to work,
but only two connections at a time on the tri switch, Wammers would know more.
Click to expand...
The dual pressure switch operates the compressor clutch and the fans. From memory there are two black wires and two coloured. If you bridge one colour to one black you should hear the compressor clutch click or the fans run. Haven't looked at the single pressure switch wiring.
 
tomcat59alan said:
The dual pressure switch operates the compressor clutch and the fans. From memory there are two black wires and two coloured. If you bridge one colour to one black you should hear the compressor clutch click or the fans run. Haven't looked at the single pressure switch wiring.
Click to expand...
I found if you take the front grill off and poke the connector block through to the front of the car, it's easier to clean and bridge the wiring.
 
Thanks. I have taken them off and cleaned up but nothing. I had assumed that I could bridge the connection and bypass the switch. Will try that when home on Tuesday, with a more experienced helper! I assume that they should be bridged one at a time? Or both together? Wammers anything to add? Please remember you are talking to a novice!! Many thanks and happy Easter.
 
Glad I wasn't going mad and was on the right track with the bridging, then again I must be mad to own a p38 and be on here:D:D:D
 
I guess you have checked the obvious first, have you got a drive belt fitted ? Have you checked the fuses ( 34,37,42,43) and relays (6 and 7). Diagnostic's the way to go after that. Not a simple wiring system, with request and grant signals etc.
 
Dual pressure switch. Pin 1 two wires. Green/white and Black/yellow. Pin 2 White/light green. Pin 3 Black/blue. Pin 4 Black. Linking pin 1 and pin 2 enables compressor. Linking pins 3 and 4 enables R/H condenser fan. There should be two switches dual pressure switch and single pressure switch clean contacts on both of them. Diag would tell you what the problem is. If either switch is sticking give a light tap to see is they will free off. If not it's another regas after changing them. If the compressor is running then cuts out could be expansion valve blocked. give that a tap on bulkhead where pipes enter cabin.
 
Thanks very much once again. When home on Tuesday, I will look at all the things suggested. Have looked at the fuses and the belt all that seams fine. Will report back when a solution has been reached!
 
Some success has been made! while looking stupidly at the relays and wondering how to tackle them with out making things worse, I spotted a little blue connector that was not connected. So I connected it. Voila, ice cold air but with the addition of a screech from the compressor. the screech isn't that noticeable from the inside with the windows shut and, disappears under load. having now had a drive up the road, the screech is no longer evident on tick over but is while trundling around. It stops when the AC button is pressed. Am I going to shed the belts or should I give it a while to bed back in?
blue connector.JPG
 
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