Trying to get my ac up and going. It has never worked since I have owned the car.

I upgraded the coolant to 134 last year.

My question - When your ac is working properly, do you find that you compressor cycles on and off or just comes on and stays on. My stays on. I would expect that when the engine is revved up, it should cycle.

What does yours do?

Jim

What were you using previously? (I suspect that you meant "refrigerant.")
The answer to that question depends entirely on the vehicle. If your system does not incorporate a high pressure cut-out switch, there is no mechanism to cause it to cycle on the basis of pressure.

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I am sure the system had R-12 at some time, but the system was empty when I got the car.

Since then I replaced the compressor and the drier, and converted to R134.

There is a pressure switch on the drier, but from my reading I have found that it just prevents the compressor from coming on if there is no freon.

But also from my reading I found that the climate control system does monitor the temperature of the evaporator, so the controller could cycle the compressor to control the temperature of the evaporator.

In any case mine does not appear to cycle and I an trying to determine if that is normal.

That is technically correct, but unless you are using the a/c in the winter, the chances of freezing the evaporator with R-134a installed in a R-12 system are just about nil.

I have R-12 installed in a '82 300D. The evaporator cut-out switch operates only on very rare occasion, like when the a/c is turned on but not really required.
It's tough to say what is normal without having the details about the vehicle in question. But, if it was originally a R-12 system, it likely doesn't have a high pressure cut-off switch. Most R-134a systems (as original equipment) have a binary pressure switch, which cuts out the compressor clutch if the pressure is too low or too high.

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Jim,

Could you give us the model and year MB you're working on?

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

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question- would these older systems be able to put out decent air conditioning performance? say an 84 300sd?

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual