AC help needed on 88 190e 2.6
 

Hi guys,

I just read saumil's AC diagnostic guide. But before checking the elctronic side I'd like confirm if the mechanical side is normal. Last summer the AC was working fine though not too cold.

At the start of this summer it didn't work at all and my mechanic said it's almost empty of freon. So we re-charged it but still the AC won't kick in. So he did his thing checking the AC components. Then we opened up the klima relay and placed a piece of paper to push the contact forward. We put it back in and this made the AC work.

My mechanic's conclusion is that I need a new klima relay. In short I don't agree with him. I re-checked the low side pressure with a cheap gauge that comes with the can. With the engine running I read 80 when the AC's off. When I turn on the AC, I see the gauge go down to 35 for a second then it goes back up to 80 (I think the unit is PSI). When I turn off/on the AC it doesn't happen anymore. But i can duplicate it if I turn off the engine entirely. I'm thinking that it might be the RPM sensor cutting out?

I also recently flushed my power steering pump and spilled some possibly on the compressor. Can this mess with the RPM readings? If yes how do you clean the compressor clutch?

Thanks,

Ben

If the compressor comes on & goes right back off then checking the compressor speed sensor would be MY next step.

All testing should be done at the klima relay connection, relay removed.
The speed sensor MUST generate at least 0.3V a/c at idle (650-750 rpm) with the compressor running.

Thanks for the response. But are my pressure readings normal? 80psi with the AC off, 30-40 psi during the short time it kicks in.

Yes

Update:

I was able to squeeze some time this morning before going to work.

Resistance = 830Ω
Voltage between pin 9 & 11 = 0.35Vac
Voltage between pin 1 & 2 = 4.6Vac

With pin 5 & 7 jumpered the AC was blowing cold. The only test not in spec is the resistance of the RPM sensor which is double of what saumil listed. But the Vac reading is in spec.

I'd greatly appreciate any thoughts if I should move on to other components.

Thanks,

Ben

Your best bet is to eliminate the whole speed sensor mess by installing a regular relay to trigger the compressor. Send me a PM or e-mail & I will send you instructions.

Hi MBDoc,

I just sent you an email. Thanks.

Ben