Air Con Assistance

[Money Pit]

Hi Everyone,

First time poster from Australia, long time lurker. I have a 4/1995 840ci and need advice with an Air Conditioning fault. My daily commute temperature of 34 deg C (93.2F) outside is finally getting to me .

Air Con failed a little over a year ago. A friend (refrigeration engineer) checked the system and found only 400 grams (0.88 lb) of gas (R134a). Long story short, we sucked it out & didnt have enough gas to put back in. I found the 30 amp fuse for the Aux Fan kept blowing. Several months later I replaced the Auxillary Fan and fuse but with an empty system no air con (as would be expected).

Prior to regassing the system in late November, we ran a series of vacuum tests and the system seemed solid. We regassed with R134a to 1.44 Kg (3.19 lb) as per label in the engine bay. Tests over 24 hours showed the system stable and no apparent leaks. Heaps of really cold air.

About a month later, air con working fine on the way home from work one day then no cold air the next morning.

I have tried a new Evaporator Temperature Sensor, swapped the compressor relay with known working relay (washers), disconnected the pressure switch (reconnected), Aux Fan fuse is good & fan does run. All fuses test OK. Compressor does not seem to kick in. I found one wire on the top of the compressor but cant get any substantial reading on the multi-meter. I think this may be for the compressor lock up control.

Could you please guide me in a process to check or test the compressor?

What are the wiring connections at the compressor and is it possible to test by applying +12v?

What are the pin connections on the compressor relay so I can test if the control unit is triggering the compressor to turn on?

I would like to try to diagnose the fault as I will save heaps of $$ by ordering the parts from the USA before I hand it over to the mechanic (again ).

Thanks in advance for your help

Philip
Brisbane, Australia
The other side of the world, south of the equator

[Timm]

All the details on the relays can be found here:

http://www.meeknet.co.uk/e31/Timms_B...lay_Finder.htm

Do a test:

Fire up the engine
Switch OFF the A/C so the snowflake LED goes out
Reduce fan speed to zero (past the click)
Get out of the car and check that the auxiliary fan is NOT running (this ensures that the coolant temperature sensor is not demanding auxiliary fan operation)
Increase the A/C fan speed past zero
Switch the A/C back on again so that the snowflake LED comes back ON

Get out of the car - is the auxiliary fan running now?

If it is, the compressor should be running - and if it isn't the most likely cause is the compressor clutch:

http://www.meeknet.co.uk/e31/e31_95.pdf#page=533

It is the compressor demand (from the DME) that actually requests the auxiliary fan to run - so if the fan runs so should the compressor

If the auxiliary fan does NOT run then let us know and we can take it from there.....

[TxGR8White]

Did you replace ALLof the o-rings in the system (about 10 or 12). This is why you are losing Freon. Once the Freon gets belowa certain level, it shuts the compressor off completely to keep it from getting destroyed. O-rings don’t last forever...

[Chamberlin]

I believe in most systems that the low pressure switch is also a high pressure switch too. Over pressure is just as bad.

[TxGR8White]

Go to realoem.com and you can get a good idea of where all the o-rings are. This is the only type of “seal” used in this system. I bought a whole box of green o-rings for the cost of 2 BMW o-rings. There are enough in that set to do at least three cars worth.

[Money Pit]

Hi All,

Thanks for the tips. I have a set of the "O" rings from FPC just in case they were needed. I cant rule out loss of gas but I don't have the gear to check it until I next visit my mate with the tools.

I followed Timm's suggestion test and found the Aux fan does not run with the air con switch either on or off with the engine at operating temperature.

I pulled the Compressor Control Relay K19, checked the socket and started having a poke with the multimeter.

I have 13-14 volts at Supply Side Pins 2 & 3 (as marked on the diagram on the relay itself) which should correspond to pins 8 & 6 on the diagram on Page 533 from Timm's post, when measured to earth. Voltage is there when Air Con is switched either off or on

I get 14 volts measured across pins 3 & 5 (again as marked on the diagram on the relay itself) which should correspond to pins 6 & 7 on the diagram on Page 533 from Timm's post.

I have no voltage measured across Pins 1 & 2 (again as marked on the diagram on the relay itself) which should correspond to pins 10 & 8 on the diagram on Page 533 from Timm's post. So Pin 10 to the DME does not have a path to earth and no change when the air con is switched off or on.

So Pin 7 to the compressor has a path to earth. I assume that if I apply +ve voltage to Pin 7 that should bypass the DME side of the relay and tell the compressor to run.

I will wait for Timm's next step before blindly poking around with 12 volts - the last time I did that I lost about a metre (3 foot) of wiring loom in a 1960's Holden (Aussie Chevrolet).

[Timm]

Your tests show that the DME has decided not to run the compressor - probably because you have no system pressure. There's loads of advice above regarding why you might not have any system pressure - but I would go to one of the cheap re-gassing people and get them to add some dye. Then use a UV torch (a fiver from Ebay) and see if you can trace the leak - I did this successfully and is detailed here:

http://www.meeknet.co.uk/E31/timms_b...eplacement.htm

[Money Pit]

Hi Timm,

Thanks. I guess its time to book it in with the Air Con experts when I next have a rostered day off work. The people I have used in the past for another car usually throw the dye in with nitrogen gas to leak test - cheaper than the R134a and doesn't have to be recovered from the system for environmental reasons. I'll post back with what they find but it wont be for a few weeks.