Mk7 Aircon problem

[tomwrc205]

Dragging up an old thread but I have exactly the same problem...

I have done exactly the same procedures as above and have exactly the same symptoms.

Have done some tests today with air con man and found that the relay in the engine bay for the air con has power but it seems that it uses a switchable Earth to activate the relay to power up the compressor?

Replaced high pressure sensor for known working one. Bridged low pressure sensor
Had all pressures checked and correct amount of gas is in the system
Have had air con working and gets nice and cold if we supply the relay with an earth.

My question is what switches the earth to the relay? Is there an evap thermostat to stop it freezing that is causing my problem? Or another switch that I'm not aware of?

Cheers

Tom

[daipower]

Hi,
I cant say I am glad to hear you have the same problem but its done my head in a bit. I wonder whether there is any hope on the dirty connector onto the pump itself, and is there some sort of back feed to earth via that or the pump itself. What is your next plan, I wish I could help but have run out of ideas. I even purchased a rad with the twin fans thinking it was that, no joy. I bridged out the relay and it worked fine, is yours the same.
thanks
Dai

[tomwrc205]

Yea mine is the same. If I supply an earth to the air con relay in the engine bay all works fine. All pressures are as they should. I just need to know what supplies the earth to the relay. I'm assuming there is a temp sensor or thermostat to stop the system freezing up the evaporator but I can't find anything regarding this?

I just need to find out where the earth supply comes from that switches the pump on and off and I should be on the right track.

Hopefully someone with a bit of knowledge will help

[ake]

The earthed relay switch wire comes from the engine ecu (PCM), as does the control wire for the fan.

The low pressure switch is also connected to PCM, via two wires, which both have to go to earth to run the AC.

If you want the wiring diagram, then let me know your email address

[tomwrc205]

Pm sent

Will post up findings when I get a chance to run through the diagram

[motovanner]

Dunno if this helps but on my 2005 van the a/c compressor " cycles " on and off - the air is nicely chilled coming through the vents.
Seems to be quite normal for the compressor to cut in and out as needed - like the fridge at home, - it doesn't run continuously 24/7.

[daipower]

Has anyone found the solution. Worked on my van today for 2hrs still scratching my head. Bridge out the R10 relay pump works fine, relay is good. Would be eternally grateful for a fix.
thanks
Dai

[daipower]

Has anyone found a solution. If I bridge out the relay to the compressor it works fine, the relay is good and has been swapped with several good ones to check just in case. Can anyone offer me a fix please.
thanks
Dai

[flashy]

I have a Ford Transit with the identical problem, its doing my head in! Have you solved your problem your end & can you help me. I've tried everything you have so far! Thanks, Geoff

[daipower]

Geoff,
No I havent, I was hoping to get it sorted on here. I think its a bad earth and the relay voltage is low and dropping out.
Dai

[flashy]

yes but it doesnt come back on.

The earthed relay switch wire comes from the engine ecu (PCM), as does the control wire for the fan.

The low pressure switch is also connected to PCM, via two wires, which both have to go to earth to run the AC.

If you want the wiring diagram, then let me know your email address

Geoff,
No I havent, I was hoping to get it sorted on here. I think its a bad earth and the relay voltage is low and dropping out.
Dai

My air con was working fine until the pcm gave out, I had it replaced & that's when my air con problems started. The high pressure switch has four wires going into it only one is showing power is this normal? A copy of wiring diagram would be great.

[daipower]

I dont know, I have the haynes manual here somewhere. Is yours a mk7

[ake]

yes but it doesnt come back on.

The earthed relay switch wire comes from the engine ecu (PCM), as does the control wire for the fan.

The low pressure switch is also connected to PCM, via two wires, which both have to go to earth to run the AC.

If you want the wiring diagram, then let me know your email address

Geoff,
No I havent, I was hoping to get it sorted on here. I think its a bad earth and the relay voltage is low and dropping out.
Dai

My air con was working fine until the pcm gave out, I had it replaced & that's when my air con problems started. The high pressure switch has four wires going into it only one is showing power is this normal? A copy of wiring diagram would be great.

Was the new PCM correctly programmed to the vehicle so that it knows it has air con?

[daipower]

I dont know what a PCM is, I havent changed it. All I have done is had the air con checked and coolant liquid changed, all good. Its just that relay, if i bridge it out the air con comes on.

[knobby1]

As Ake says...if the PCM has been replaced it'll need to be coded in using IDS, otherwise it's an expensive paperweight.

They're basically dumb....and will only do what they're told to do...if they haven't been told they have air-con...they won't know it's there.

Lord Knobrot