Thanks Paul, my local mechanic about 1 1/2 ago actually tool the car to the local Cadillac dealership in northern California who repaired the system. My guess is that they never touched any of the rear air controls.
So I can assume that the "unk" switch probably activates the AC compressor when the engine is running, in case the front AC is not turned on ?
Don't know what the "unk" switch does, but whatever it does, will not do any harm if you turn it on. When you turn it on, have the doors closed, so if it illuminates a light in the rear, you will know immediately. With the switch in the ON position, and the engine stopped, and the front air conditioning lever set to off, start the engine with the hood opened, and see if the compressor is turning. If it turns, then go to the rear, and turn the switch off, and if the compressor stops, then you will know for certain that is what activates the rear air conditioning when the car is running, and the front air conditioning is in the off position.
So Paul if the repairs were completed without touch the rear air, would they still have had to use the same amount of refrigerant/freon? looks like they converted the system from R-12 to R132
In theory yes. When converting from R12 to R134, the formula is to use 80% of the specified quantity of R12. Assuming that your car originally called for 5 pounds of R12 refrigerant, then the correct amount of R134 refrigerant would be 4 pounds. Some shops don't use a refrigerant scale
to install the refrigerant, and keep installing refrigerant until they see the refrigerant running clear in the sight glass at the top of the receiver drier.
Converting a system from R12 to R134 requires changing the type of oil in the compressor, flushing the system of the old oil, and replacing the some additional components. To what extent the dealership did all these things is difficult to know, unless they itemized them on the invoice. This is why I personally don't like switching refrigerant from R12 to R134. The time (dollar cost) to do this correctly vs. the higher cost of using the more costly R12 works out to being equal usually. The R134 molecule is smaller than the R12 molecule, and the old rubber hoses that were able to contain the R12 molecule, can't contain the R134 molecule as well. When the automakers switched to R134, the hoses also changed from a reinforced rubber hose to what is known as "barrier" hose. This hose has an internal material that can contain the R134 molecule. On my 1962 Chevrolet, I had to replace all the rubber hoses, since they were hard and no longer able to contain the refrigerant without its leaking out in a few days. Since the original rubber hoses were no longer available, I used the new barrier hose. I also refilled the system with R12, since that is the refrigerant that it was originally designed for.
By turning on the rear air unit, engine running, I really can't un-do any of the repair work that was done for the front system?
There is nothing that you can do damage to the system by turning on the rear air conditioning switch that will un-do any of the previous repair work. If you find that the rear air conditioning doesn't work, and the front air conditioning is working properly, then the fault lies in the rear air conditioning unit. Most likely, it is a defective expansion valve, which will require the entire system be evacuated to replace the expansion valve. If this is the case, it will be up to you to determine if its replacement is cost effective.
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