Help with A/C Compressor problem 1991 300se - PeachParts Mercedes-Benz Forum

nsein · #1 05-14-2009, 06:08 PM

Professionally converted to R134a approx 5 years ago: Pressure good, freon good, no leaks. MB shop was going to replace compressor but when I drove it in next morning it was working.

Here's how it goes, car cold: crank A/C works fine. Don't turn car off drive forever A/C works fine. Turn off car at any point to go in store whatever, compressor will not turn back on. Any suggestions? Thanks in advance.............Nate

slk230red · #2 05-14-2009, 06:16 PM

Quote:

Originally Posted by nsein

Professionally converted to R134a approx 5 years ago: Pressure good, freon good, no leaks. MB shop was going to replace compressor but when I drove it in next morning it was working.

Here's how it goes, car cold: crank A/C works fine. Don't turn car off drive forever A/C works fine. Turn off car at any point to go in store whatever, compressor will not turn back on. Any suggestions? Thanks in advance.............Nate

The first thing I would check is the pressure switch. When you start the engine and the compressor doesn't turn on, pull the connector off and short the 2 wires and see if the compressor turns on.

nsein · #3 05-14-2009, 06:19 PM

I will try that now and reply here in a few.........

nsein · #4 05-14-2009, 06:32 PM

Viola it worked! When your connect the 2 wires it takes a few seconds but then the compressor starts! So my next question is in order to replace the sensor you indeed have to breach the system correct? Also what kind of trouble will I get in if I just leave them direct connected for the time being? It is 100 degrees here

tinypanzer · #5 05-14-2009, 06:42 PM

You definitely do not want to leave that switch bypassed. An explosion could result.

nsein · #6 05-14-2009, 06:45 PM

I will have to completely empty and refill the system though correct?

tinypanzer · #7 05-14-2009, 07:11 PM

Unless you are incredibly quick, yes you will have to dump your charge.

slk230red · #8 05-14-2009, 07:20 PM

Quote:

Originally Posted by nsein

Viola it worked! When your connect the 2 wires it takes a few seconds but then the compressor starts! So my next question is in order to replace the sensor you indeed have to breach the system correct? Also what kind of trouble will I get in if I just leave them direct connected for the time being? It is 100 degrees here

Quote:

Originally Posted by tinypanzer

You definitely do not want to leave that switch bypassed. An explosion could result.

It wouldn't be good to leave it bypassed. If your Aux. fans failed to operate the high side would get extremely high, or, if you lost freon the compressor would not turn off and would be damaged. It's a compressor protection device.

So, to repair it correctly, you would need to get the correct pressure switch for your car, remove freon, probably replace the drier/receiver too, vacuum system and recharge.

BTW, have you connected a set of gauges to your system to verify pressures? And, why did your mechanic want to change out your compressor? Very expensive item.

nsein · #9 05-14-2009, 07:30 PM

They are the the ones who charged it actually and checked for leaks and what not. When it would not come on I guess he figured it was toast. But when I returned the next day ( the day they were to replace the compressor ) with it working they said no reason to spend the $ if it was working. They have ordered the sensor and will install it and put my freon back in for $150 so I will just let them do it. That way I know it's done right instead of Dr. Shadetree AKA "me" LOL. So luckily I will only have to suffer until tomorrow. Thanks a ton for the image and a quick read on my diagnosis. I am very appreciative...........Nate

tinypanzer · #10 05-16-2009, 12:24 AM

Quote:

Originally Posted by slk230red

It wouldn't be good to leave it bypassed. If your Aux. fans failed to operate the high side would get extremely high, or, if you lost freon the compressor would not turn off and would be damaged. It's a compressor protection device.

A mechanic friend once told me that he did that on a Ford Escort, and it worked for a very long time. Then one day BANG! the evap blew open and the car filled with R12 so fast the driver almost lost consciousness from asphyxiation. It was his girlfriend.....

I never did ask if he knew beforehand that it would do that