I've recently bought a 1985 300CD that has a brand new compressor. Freon was added and I was told it blew cold air. I had the car shipped from California to New Orleans and lo and behold, it's not blowing cold. Called the mechanic in CA, he remembered the job and suggested that the a/c clutch may not be engaging. He said I should "touch both wires together" on the low pressure switch on the receiver/dryer. I've dug around the forums and have come across the term "jump the 2 terminals."

Question: Are these two the same thing. If so, what exactly does that mean. Novice here, so type slowly

Yes, they mean the same thing. If the system is in need of a recharge, the low pressure switch will not allow the compressor to engage. This prevents the compressor from being damaged. When you do "jump" the terminals, you should see and hear the compressor "clutch" engaging. If the clutch does not engage, it usually means that their is a problem with the clutch or compressor. Word of caution, do not run the test for more than a few seconds at a time, or you could end up damaging the compressor. Good luck

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96 E300d

Note: I copied this pic. It's not mine (Thanks 420Benz). So, the process itself. The red is high pressure, the other low pressure and the low pressure is the one i want to jump. How do I do "jump" it?

Better yet, do the test with the engine off. Or just check the switch for continuity.

The red switch is not related to the compressor. You want to jumper the wires that connect to the lower switch.

Yes, it's the silver one, not the red one. Touch the two wires together with the key on and engine off. Listen for the clutch to click in. If the clutch is working it will be easily heard.

If it does click in with the wires shorted together, then it is time to put gauges on the system to see if there is any charge left.

Awesome. I love this website! Thank you guys.

If all you are trying to determine is if the compressor is engaging or not you can do that just by looking at it. The center of the compressor pulley is attached to the compressor while the pulley itself is free to spin with or without the center part turning. If you have the car running and the A/C on and look at the middle of the pulley at it is standing still then the compressor is not running. If it is not running then I would next suggest putting some gauges on the hoses and seeing if there is any refrigerant left in it. You will need to know if it was converted to R134a or still uses R12 to know what fittings you need on the gauges.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

It was converted r134r per California emissions law. The mechanic in CA mentioned to me that in 1985 they made this car already w/ the conversion and the air filter located in the front of the engine rather than on top. Long and cylindrical rather than short and squat. A more expensive filter too.
Thanks. I'll go take a look once this rain clears up.

Air filter placement has nothing to do with the A/C. Also, is was in the mid 1990's that 134a became required in new cars. My '97 Nissan P/U that I owned had 134a. My brother's '95 T-Bird also had 134a. I forget which exact year it was required for all new cars to have 134a.

The air filter placement was due to adding a trap-ox to the exhaust system. There wasa recall due to plugging and turbo damage. That was on Californai emissions. Some have swapped in Federal setups.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

It sounds like he is being told that the 85 cali model was originally supplied with 134a due to the stricter CA law. That does not sound correct to me, I assume it was converted later (in CA). Can anyone anyone verify that?

Seems not:

Thanks, that's what I thought.