A/C not switching on

[wolfador]

Working on getting the A/C going on my 86 325e - stock M20B27

Symptoms:

• A/C light on switch doesn't turn on, clutch doesn't engage, low aux fan doesn't turn on.
• Blower does work w/without A/C turned on

So far I've replaced:

• Aux fan resistor
• both high/low temp switches
• low pressure side a/c hose (had a gash + leaking)
• high pressure a/c switch (used)
• a/c switch in dash (used)
• A/C holds a charge (checking low side) and shows in the "green" zone with my refill can

Followed through steps in https://www.r3vlimited.com/board/sho...56&postcount=7 and aux fan works when jumped with either high/low switch.

compressor clutch engages when jumped with 12v

No power at pin 86 on K1 relay (key on, engine off)

[Mike36]

Does the A/C switch button stay pushed in?

[wolfador]

Does the A/C switch button stay pushed in?

It does, also the recirculation button does light up when pressed. (forgot to mention that) :D

[tomstin]

Two things: 1) Verify the evaporator temp sensor is working. 2) Are the temp sliders in the right place? Could be a problem with that mechanism (check the wiring diagrams).

[wolfador]

Two things: 1) Verify the evaporator temp sensor is working. 2) Are the temp sliders in the right place? Could be a problem with that mechanism (check the wiring diagrams).

I'll test the evap temp sensor. I only have the one dial for the "temp" is that the slider you're talking about? The 3 sliders I have are to direct the air (windscreen, center, floor). The temp dial seems to work correctly. If I turn it to hot I get full heat.

I tested the high pressure sensor and didn't get 12v on either of the pins. Could it be the low pressure sensor, haven't checked that yet? I think their wired in series, not sure which one first though.

[wolfador]

Looking at the wiring diagrams I think the "temp sliders" are the air direction sliders. Looks like since its an "early" both the bottom and middle sliders need to be open.

Will try that in the morning. Thanks!

Also confirmed its the low and then high switch in series.

[wolfador]

After moving the middle/bottom sliders to the right and turning on the ac the light now comes on but still not compressor action.

I do/did have to give the whole panel a push in to get the light to trigger/stay illuminated I guess something is loose back there, prolly when I pulled it to get to the OBC light.

However with the light illuminated still no power to the low or high pressure switches so I'm guessing it is the evap temp switch as that should provide power to those switches and the aux fan didn't come on either.

Will have to see if I can bypass that and see if that works.

[wolfador]

Looks like I have a "evaporator temperature switch", so bypassing that switch the aux fan comes on and the compressor kicks on. After refilling it back up again everything seems to be working but still no cold air :(

[dsphil]

You didn't just refill the AC system with those off the shelf refill cans that comes with the hose, did you?

[wolfador]

I did, the PO had already added the R134a valves to the hoses but I prolly should have gotten a vacuum pump and pulled the air out.

It seems like there is air in there as after I disconnected the recharge can I could see bubbles at the valve. after letting that sit for a few hours I reconnected the can and it was low in pressure again. After adding some more from the can the a/c is performing much better and doing about -20 degrees of ambient.

As it also seems to be pulling the humidity from the air it's way better then just the air blowing so I'm pretty happy with it. Will monitor over the next few days and see how it goes.

Thanks all!

[jeffnhiscars]

Pulling a deep vacuum is critical and attempting it without a micron gauge I just rolling the dice.

[dsphil]

I did, the PO had already added the R134a valves to the hoses but I prolly should have gotten a vacuum pump and pulled the air out.

It seems like there is air in there as after I disconnected the recharge can I could see bubbles at the valve. after letting that sit for a few hours I reconnected the can and it was low in pressure again. After adding some more from the can the a/c is performing much better and doing about -20 degrees of ambient.

As it also seems to be pulling the humidity from the air it's way better then just the air blowing so I'm pretty happy with it. Will monitor over the next few days and see how it goes.

Thanks all!

Don't worry. The worst it could happen to the system is it might explode when pressure gets too high with that much air trap in the system. By next summer you might just need to replace AC compressor, expansion valve, condenser, or hoses. At least for right now you know the system runs. Good luck.