Troubleshooting AC on 95 E300D

[shertex]

Caveat: I only know enough about AC systems to be dangerous.

Would be happy to get the AC on this 95 E300D up and running....but not willing to invest any significant money.

The system is pressurized (presumably with the proper refrigerant), but compressor won't engage. However, when I briefly jumper the low-pressure cutoff switch, the compressor engages. Perhaps I have a bad switch?

What are some other simple things to check and/or common failure items?

Thanks.

[Mölyapina]

I remember that we had this problem on our Corolla earlier this year -- good pressure, but no compressor engagement. A $13.99 fan clutch relay ended up solving it.

[DrLou]

When you say 'pressurized' - have you attached gauges to system and checked?

Before assuming the low pressure switch is bad, consider that you might just have... low pressure.

A system with a leak can remain relatively pressurized, yet not quite pressurized enough to kick the compressor on. I've just been stepping through a system rebuild myself, for precisely this reason.

A leak test is always a good place to start.

[shertex]

Originally Posted by DrLou

When you say 'pressurized' - have you attached gauges to system and checked?

I checked low side pressure and it's plenty high to cause the compressor to engage.

I am wondering if that relay is a likely culprit....I had one go bad on my 92.

[vstech]

if pressure is above 75psi, but compressor will not engage, and jumpering the low pressure switch lets it run, you need a new switch. you can leave it jumpered and check the pressures and temps, and if it's ok, you can safely use the a/c this way. but YOU will need to monitor the system for pressure. with out the LPS safety, you can destroy your compressor, and the entire system by drawing in moisture if there is a leak...

[shertex]

Go figure....I jumpered switch again and this time the compressor does NOT engage. Sigh....

[Mölyapina]

Is there another relay in the car that you could temporarily swap over to the AC to see if it is a relay problem or not? For example, our Corolla uses the same relay for the AC clutch as it does for the horn, so I just made sure that the horn worked and then swapped the relays. Lo and behold, the AC came on!

[shertex]

Originally Posted by Jooseppi Luna

Is there another relay in the car that you could temporarily swap over to the AC to see if it is a relay problem or not? For example, our Corolla uses the same relay for the AC clutch as it does for the horn, so I just made sure that the horn worked and then swapped the relays. Lo and behold, the AC came on!

To the best of my knowledge, there's only one relay like that in the car.

[chronometers]

When I replaced the wiring harness with one I had rebuilt, I noticed one of the connections controls the AC system. Have you had any issues with your harness and the switch(es) it is connected to? Don't want to send you down the wrong hallway but you might want to consider.

[shertex]

Originally Posted by chronometers

When I replaced the wiring harness with one I had rebuilt, I noticed one of the connections controls the AC system. Have you had any issues with your harness and the switch(es) it is connected to? Don't want to send you down the wrong hallway but you might want to consider.

The PO removed some stuff at one point, so that's certainly a possibility.

The main thing that's confusing me now is that I'm certain I was able to get the compressor to engage by jumpering the switch (this was a few weeks ago), but now I can't.

[Zulfiqar]

sounds like a dodgy klima/kickdown relay if you get no A/C compressor engagement at all with low pressure switch wiring shorted and the A/C set to cool from the pushbutton unit.

It may also be a bad magnet clutch on the compressor.