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Discussion Starter #1
It finally is warm enough that I needed the AC in 92 164S, I turn it on and hot air. I check the compressor and it is not coming on, researched and see that it has a pressure switch that will keep the compressor from engaging if the freon is low. The car has been converted to R134A but still has the R12 low pressure valve. According to the service records from the PO the AC was last serviced in 2010. My thought is to top off / refill the freon and see if that solves the problem. Is there is anything else I should check first?
Thanks
 

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It is best to put a gage set on the system and check low and high side to see if any R134a left in the sytem. Then evacuate system with a vacumn pump and a recovery unit to recover any freon left in the system.

If system was not empty you can recharge system with some leak check dye and couple oz of ester oil and 36 oz of R1134a.

Then do a leak test with black light and/or a sniffer and do a system operational test checking out for proper low and high side pressures, radiator cooling fan operations low and high speed. Low speed is what a/c system controls if car is wired in stock format.

Here is John's tutorial on process of conversion and servicing: http://www.alfabb.com/bb/forums/1162497-post131.html

I just reserviced 164S. I had about 24 oz left in system so real slow leak somewhwere not enough to worry about. I did the complete evacuate with pump and recharge but if you have some freon in system you can add some and using gage set moniter low and high side pressures once compressor clutch engages to see when you have enough freon to give you about 30-35 psi on low side and radiator cooling fan will kick on when high side gets to about 215psi.
 

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Assuming you still have some pressure in the system, go ahead and refill. 36-40 oz of R134a fills the system from empty, so it'll be somewhat less than that.

If it's been 5 years since it was topped off, it's likely that the old R12 hoses have allowed the refrigerant to seep out. I did not change my hoses to barrier hoses either and I lose about 12-16 oz per year. I just take 15 minutes to top it off in the spring.
 

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Discussion Starter #4
Thanks, I had to order R12 gauges and hoses, all of my recent vehicles have had the R134A fittings. I'll let you know how it goes.
 

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The high and low pressure valves should have R-134 adapters on them. Usually available at any auto parts store.

Since you infer that they don't have those adapters, but there's R-134 in the system, I think it could be HIGHLY questionable that the R-134 conversion was done correctly. How sure are you of the quality of the conversion?

If done shade-tree cheapo, it's likely that it can trash the entire system . . . . . causing a VERY expensive repair including minimum new condenser, compressor, dryer, expansion valve, plus flushing and cleaning of the hoses and evaporator.
 

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Discussion Starter #7
Richard (greybeard) thanks for the heads up on the reversion back to R12, I overlooked those service receipts in your excellent records.
Found a father son shop here in Old Town that specialize in foreign cars, the dad has owned a 164 & Milano, they did a complete system service and re-charge with R12, I need to wear a down jacket now.

Next project is stepper motor gears!
 
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