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D2 Air Con Pressure Switch Testing


v8Dougie
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Hi all, bit of back ground, have a 2003 D2 v8 which I have never had the air con working on. When I bought the car, it was sold with a replacement air con pipe, the infamous one which goes through the slam panel to the dryer, as I was told this was leaking. This replacement pipe was fitted during an engine change, and the system regassed. I was told it was good, holding vacuum and pressure, however the system would still not work. That was some 6 months ago, and now it is warm I need it fixed!

Did a bit of fault finding today, compressor fuse and relay okay. Fan relay okay but 40amp fuse blown, replaced fuse and bridged relay but fan still wont operate, checked voltage to fan and all okay, couple of smacks with a rubber hammer and the fan tries to turn but can't, so I have a seized fan, one thing to change.

Carried on and checked the voltage to the compressor, nothing. Removed the connector on the pressure switch behind the front grill, bridged the connector loom side and the compressor kicked in fine. Came on and off with the ECON switch on the heater controls too. So I figure it indicates either no gas in the system, or faulty pressure switch.

Can someone confirm if this is just a high pressure switch, or both high and low. If the latter thought it needed three wires? Also, if just a high pressure switch then either the pressure is too high (unlikely as system not working!) or the switch is faulty.

Any way of testing the switch? I assume it should be closed when it is happy, allowing the signal to pass through it. I am happy to regas the system, but don't really want to do that if I have then have to drain again to change the pressure switch.

Any help much appreciated!!

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Try applying power to the pump clutch - and see if you get cold air. So long as you stop as soon as you can decide if it feels cold (or hot on the condenser) it won't do any damage.

In the system there is normally a low pressure switch which controls the pump clutch. When there is insufficient gas, it switches the system off. The high pressure switch (between the pump and the constriction before the evaporator) is used to switch the condensor fans on. The pressure increases sharply if the condensor is getting too hot. Sometimes there is just a thermostat on the condensor to switch on the fans - but using pressure is faster & more reliable.

If it produces cold air - it could be that the low pressure switch is faulty. If with the switch bypassed you get a similar amount of cooling as you would expect - I would just leave it bypassed for the time being. It would be worth getting the pressure tested. If it's OK then the switch is faulty. If not then you likely still have a leak.

Si

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Thanks for the assistance chaps. I did as suggested and jumped the pressure switch for about 5 mins, nothing but warm air in the car, compressor was running.

Now sat in Kwik Fit getting it regassed.I know it might not be everyone's choice for air con, but they don't charge if they can't do it and no other air con people I have found do that!!

I will update once I have driven of whether it is nice and cold or still horrible and warm!!

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Update...regass done, air con blew nice and cold, went to move the vehicle and one of the guys noticed the gas was pouring out of the front of the car, quick investigation and the pipe going through the slam panel has failed in the normal way so major leak!!

Guy was purplexed as the "computer" said it passed the vacuum test. Tried explaining to him about the difference between a vacuum and pressure test, and the reason why the car had "passed" unfortunately I think I just blew his brain!!

Anyway, pressure switch doing it's job perfectly so thread finished!!

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