‘85 eta a/c won’t stay engaged

[acarpenter86]

I’ve got a very well kept eta that is driving me crazy. The a/c won’t stay engaged. It’s hot! I can feel the air start to cool and it feels great, then the snowflake light goes off and the air warms. If I leave the switch engaged, it’ll come on a little while later for a few more seconds and the cycle repeats.

Is there some kind of sensor? Sliders acting up? (Just learned those can affect a/c but haven’t driven the car yet to play around), The charge seems ok, MAYBE a smidge low, but I can’t imagine this car is that high tech to shut it down due to a very slightly low charge.

This is an r134a system by the way.

[tomstin]

A few thoughts. The air duct sliders have to be in a specific position for the AC to work. That can be a problem. I had that area apart for another reason and jumpered around that. Also, there is a low temperature switch in the evaporator. It is up in the driver's foot well a real pain to reach. That could be acting up. Then you have the low / high pressure switch on the drier. I think you're going to have to break out the multi meter and wiring diagram to see if you can track down the problem.

http://wedophones.com/Manuals/BMW/

[D3R3K]

Also check and make sure your AUX fan is comming on out front, if the fan doesnt work the condensor doesnt cool which causes the pressures to go too high, causing it to cut the system off till the pressure goes down

[acarpenter86]

Appreciate both posts. I’ll check all of this today.

[acarpenter86]

Aux fan does come on when compressor doesn’t. Played with all slider combos and it still kicks on and off. I’m leaning toward a switch or the temp sensor. Would there be a way to number the sensor to confirm or does it look for a certain reading? It’s been a minute since I did much electronics work and I wasn’t very good then. lol

[D3R3K]

Aux fan does come on when compressor doesn’t.

What do you mean when it doesnt?

it looks like it has a temp switch not a sensor(which means it doesnt measure the temp it just switches over when it reached a certian temp) , you could remove it from the box or unplug it and jump the wire to rule it out, i attached the a/c diagram for your year car maybe it will help, let me know

[acarpenter86]

That was a typo-
it was supposed to say the aux fan comes on when the compressor *does*.
thanks- I’m about to go out and try to find the sensor and jumper it as a test.

[acarpenter86]

What do you mean when it doesnt?

it looks like it has a temp switch not a sensor(which means it doesnt measure the temp it just switches over when it reached a certian temp) , you could remove it from the box or unplug it and jump the wire to rule it out, i attached the a/c diagram for your year car maybe it will help, let me know

Is the evap probe sensor just under the kick panel, or will I need to pull the console around the center/shifter? Looking around under the kick panel, I don’t think I see it.

[D3R3K]

https://www.r3vlimited.com/board/forum/e30-technical-forums/general-technical/221890-evaporator-temperature-regulator

found this that may help, not sure where exactly where it is though

[acarpenter86]

Thanks. I get voltage at the pressure switch intermittently just like it normally does. So that tells me it has to be pre-pressure switch. Going to try to find this sensor and jumper it.

[acarpenter86]

Well, for the life of me I can't find that probe / evaporator temp sensor. If anyone knows where I should be looking or if I need to pull of the dash where the a/c controls are, please say so. Giving up for today. We are taking this car to a concert and luckily some rain blew in cooling things off. Lol.
Here is what I believe my exact part looks like. Just cannot seem to find it. https://www.fcpeuro.com/products/bmw...or-64511377476

[D3R3K]

https://www.bimmerfest.com/threads/project-323-from-the-ashes.631265/page-13

this has some good info, looks like the sensor may be above the gas pedal

[tomstin]

The evaporator temp sensor is above and to the inside of your gas pedal on the side of the heater / AC box. As I recall, you need to pull the console and remove the flexible air duct. It is NOT easy to see or access. Here is a link but I couldn't find a better picture of the backside. Once you find it, take the two wires off and jumper between them to verify its the problem. It's a pain to replace.

https://www.ecstuning.com/b-genuine-bmw-parts/temp-switch/64111374830/

[acarpenter86]

The evaporator temp sensor is above and to the inside of your gas pedal on the side of the heater / AC box. As I recall, you need to pull the console and remove the flexible air duct. It is NOT easy to see or access. Here is a link but I couldn't find a better picture of the backside. Once you find it, take the two wires off and jumper between them to verify its the problem. It's a pain to replace.

https://www.ecstuning.com/b-genuine-...h/64111374830/

Thank you!! That is not the part I was looking for. I actually saw that yesterday and didn’t realize that was it.
unfortunately, I jumpered and am still having my short cycles even with the pressure switch also jumpered. I am about to check voltage at the temp switch jumper.

[acarpenter86]

So in my case, power is getting cut before the temp switch. It seems to be cycling longer but still goes off sometimes. Is this by design? Maybe something up with the switch or the slider business? I don’t see anything else on the wiring diagram that was cause it to cut off. By the way, testing was done while both temp switch and pressure switch were jumpered.

Edited to add- short test drive. Definitely staying on longer. My theory is the sliders are acting up. I played with them and it did seem to kick it on once or twice. I’m going to try the slider bypass and report back.