Evaporator Temperature Sensor

[85chedeng300D]

Good evening Gentlemen!

Condition: The AC system used to be charged with R134a, then was recently converted back to good ole, more efficient R12.

Symptoms:
On '84 300 CD, the AC compressor shuts off even when the temp inside the car is not yet cold. The AC would cycle on and off even when the ambient temp is above 90 deg, car is at idle, and both windows are rolled all the way down, with the fan at the hi/fast position, the the temp wheel/tab is on the min/blue position. The AC now cycles cold-not cold-cold not cold. The AC don't do it when it was still R134a until it was converted back to R12. But it never got cold when it was R134a, except when it is raining or driven at night.

Questions:
1) Could the Evap temp sensor be the culprit?
2) Is there any way to adjust or tweak this to cut OFF late, probably at least before freezing point, around 34 to 36 deg F? Right now, it seems like it is cutting off somewhere around 42-45 deg F. If there is a way to adjust, can somebody please teach me how to do it?
3) Is the Evap temp sensor NFG, or MB was just too conservative to adjust this to cut OFF at a higher temp, so a new ETS will fix the problem?

But before I start changing and buying new part, I just wanted to try if adjusting it will do the trick. "I don't work at the dealer, which means I am not a parts changer and I'm trying to be a real mechanic"
I may have no idea what I am doing but if it's broke, then it has to be fixed, and the worst thing that can happen is for me to tear it up some more. Remember, "If it ain't broke, don't fix it"?

Any help, ideas, suggestions, and knowledge will be greatly appreciated! Thanks in advance!

[tangofox007]

The design "trigger" temp for the ETR is 36-40*F. Others have reported success adjusting the ETR via a screw on the switch.

For troubleshooting purposes, you could try jumpering the ETR and see if that solves your problem.

[85chedeng300D]

Originally Posted by tangofox007

The design "trigger" temp for the ETR is 36-40*F. Others have reported success adjusting the ETR via a screw on the switch.

Thanks Tangofox! I was doing my research on the search tab but no success on finding what exactly I'm looking for. I'm trying to find out if clockwise or counter-clockwise? I guess I'll just have to do it old school, tweak it, test it, break it, then "rep-it"(repeat).....

[85chedeng300D]

Does anybody know what kind or how much resistance on the multimeter should I expect on the 2 probes of the ETS to verify if I'm within the MB specs of 36-40 deg? ....and should the resistance go up or down if i want to bring it to around 34-38 degF?

[jkoebel]

83-612 Testing temperature switch in regulating valve

Note:

A test is required if cold air is blown into legroom below 40°C (104°F) coolant temperature.

This function test can be performed only with completely cooled down engine at am ambient temperature below 20°C (68°F).

With the cold engine, coolant temperature below 20°C (68°F) the blower should not start at "AUTO-HI" or "AUTO-LO". As soon as the coolant has attained a temperature of approx. 40°C (104°F) the blower should start.

However, in position "DEF" the blower should also start immediately at coolant temperature below 40°C (104°F).

Testing:

1. Switch-on ignition, but do not yet start engine.

2. Actuate pushbutton switch in following sequence, paying attention to respective function of blower.

Pushbutton Switch Blower Remedies

1. "DEF" should start.
2. "OFF" off
3. "AUTO-HI" off
4. "AUTO-HI" and start engine only after attaining approx. 40°C (104°F) coolant temperature.

Test vacuum system according to function diagram 2, (80-604).

1. Start engine and accelerate shortly several times (coolant temperature > 40°C, 104°F). This will evacuate the vacuum system.

2. Move automatic climate control to "AUTO-HI", blower should start.

3. Switch off ignition. Switch-on air again after approx. 10 minutes without starting vehicle engine. Blower should start immediately (main switch [19] still activated with a vacuum). If the blower is not starting, the line system has a leak. Check vacuum system (83-614).

[compress ignite]

I believe I saw over on GSXR's web site how he'd soldered a couple of resistors
onto the ETR to lower the compressor "Cut Out" temperatures.

http://www.w124performance.com/images/

[85chedeng300D]

What I'm really trying to find out is how to adjust the ETS on an '84 300CD, with 617 engine and 123 chassis. It's pretty much like adjusting the ALDA, but I want to know how many or how much turns and which way, CW or CCW. I just want to adjust it so the AC compressor with shut off late or at lower temps, because right now it is cutting off way to soon, even if the temp is not yet as cold as it supposed to cut off.