Wiring a Switch for AC compressor - PeachParts Mercedes-Benz Forum

bpeters2 · #1 06-20-2011, 09:56 AM

I've been having some issues with my AC compressor. Sometimes it just won't turn on wen its supposed to. Problem is totally intermittent (but frequent), no pattern to when it starts or when it decides to work again. Once it does turn on it works great...I think its an issue with the climate control system not sending the signal to the compressor to engage. Is it possible to install a new switch which would run 12v to the compressor and engage it when I needed it. The only issues I can think of is if 12v is not the proper voltage to send. I could fuse it if necessary. If this has already been discussed I'm sorry, but my wife refuses to drive in the car without AC

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vstech · #2 06-20-2011, 10:07 AM

if it's not engaging something is wrong. it's best to find out what.
likely the freeze switch is intermittent.

I have wired in 12V, it works. but there is NO protection from freezing/overcharge/leak...

bpeters2 · #3 06-20-2011, 10:35 AM

Where is the freeze switch and how can I test it. Thanks for the help

tangofox007 · #4 06-20-2011, 10:41 AM

Quote:

Originally Posted by bpeters2

The only issues I can think of is if 12v is not the proper voltage to send.

Not saying a switch is a good idea, but you should "switch" the relay, not the compressor directly.

Better yet, troubleshoot the problem and fix the real issue.

The "freeze switch," properly known as the evaporator temperature regulator, is located in the evaporator housing. Remove the passenger side kick panel to access. For test purposes, you could jumper around the ETR.

Quote:

Originally Posted by bpeters2

...but my wife refuses to drive in the car without AC

.

A wife who doesn't follow orders? Now that's a real problem. On the positive side, a wife who isn't driving isn't out shopping, either.

lutzTD · #5 06-20-2011, 11:12 AM

Quote:

Originally Posted by tangofox007

Not saying a switch is a good idea, but you should "switch" the relay, not the compressor directly.

Better yet, troubleshoot the problem and fix the real issue.

The "freeze switch," properly known as the evaporator temperature regulator, is located in the evaporator housing. Remove the passenger side kick panel to access. For test purposes, you could jumper around the ETR.

A wife who doesn't follow orders? Now that's a real problem. On the positive side, a wife who isn't driving isn't out shopping, either.

HSN delivers........

bpeters2 · #6 06-20-2011, 12:03 PM

I'm assuming that the ETS switch will not be the only component in the pass. kick panel. How can identify it? Also...kick panel: is that the area under the dash under pass seat area or is it on the right side (outside wall of car) near the pass. feet? Thanks

tangofox007 · #7 06-20-2011, 12:15 PM

Quote:

Originally Posted by bpeters2

I'm assuming that the ETS switch will not be the only component in the pass. kick panel. How can identify it?

http://catalog.peachparts.com/ShopByVehicle.epc?q=1985-Mercedes--Benz-300d-Climate--Control&yearid=1985%40%401985&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6193%3AED%7C10000135%3AMBC%7C1504%40%40300D&catid=242213%40%40Climate+Control&subcatid=242253@@A%2FC+Evap+Temp+Sensor&mode=PD

Quote:

Originally Posted by bpeters2

Also...kick panel: is that the area under the dash under pass seat area or is it on the right side (outside wall of car) near the pass. feet? Thanks

Above the passenger's knees.

leathermang · #8 06-20-2011, 04:13 PM

You still want to run your power through the low pressure switch on the Rec/dryer.... or that last potential Vstech mentioned... leak....could fry your compressor once you have no way to transport lube via refrigerant...
Perhaps that switch is being a problem.. or perhaps you are marginally low on refrigerant.... that is not a static system... it moves around in there... so readings will vary ... so you might want to check basic refrigerant level.... by pressure readings and temps at the center vent.... replacing the low pressure cutout will require evacuation of the system since it is in contact with the refrigerant... unlike the temperature switch also on the rec / dryer...

bpeters2 · #9 06-21-2011, 09:17 AM

Thanks for the help. I assume that if I start the car up after it hasn't been running. Engage the A/C via control panel, then I should have continuity across the two terminals on the ETS sensor. Is that correct?

tangofox007 · #10 06-21-2011, 09:25 AM

Quote:

Originally Posted by bpeters2

Thanks for the help. I assume that if I start the car up after it hasn't been running. Engage the A/C via control panel, then I should have continuity across the two terminals on the ETS sensor. Is that correct?

You should have continuity across the switch any time the temp is above 36*F. Below 36*, the switch opens to disengage the compressor clutch so that the evaporator does not ice up.

ETR switches are known to get flakey and open at much higher temps. Some adjustment of the trigger temp is possible.

Johnt49 · #11 06-21-2011, 10:14 AM

There are relays mounted on the CCU board. If you determine the problem is no power coming from the CCU you can take it apart and clean the contacts on the relays with a piece of 220 emery folded over (like a nail file). This will clean both sides of the contacts at once and could very likely solve your problem. I've done this on mine & it's working fine 4 yrs later.

tangofox007 · #12 06-21-2011, 11:05 AM

Quote:

Originally Posted by Johnt49

There are relays mounted on the CCU board. If you determine the problem is no power coming from the CCU you can take it apart and clean the contacts on the relays with a piece of 220 emery folded over (like a nail file). This will clean both sides of the contacts at once and could very likely solve your problem.

Cleaning the relays in the CCU absolutely will not solve the problem. Those relays have nothing to do with the a/c compressor operation.