71 Cutlass S 350 4bl factory air - bought the car exactly a year ago - the ac worked - but not really well. This summer I have no cold air at all. The previous owner switched the car over to 134a, but it looks to me like it is all stock parts. Obviously the high and low pressure ports are the new 134a type now, but is that all you do to change over? Change the gauge ports, and fill it with 134? I thought I read somewhere that the 134 leaks out of the older systems - is this true? Do I need to change my compressor - or hoses or anything else - or just find the leak and recharge it?

OK now to the recharging part - I know we always used to pump the system down with a vacuum pump - then charge them with r12 back in the day - is this still the same procedure for 134A? The kits I see at the auto parts stores say no vacuum required - but is that true, as long as I still have some pressure in my system (which I do) will the kit work to get me cold air again? Do the kits with the stop leak actually work - or do they do more harm than good?

Thanks to all who may respond - I am sure someone must know AC well enough to answer my Q's.

 

The POA valve (or STV) will have needed removal and recalibration for use with r134. If not calibrated, pressures will not be high enough for 134 to cool like it should. Can you tell if it was removed? It is the thing plumbed into the evaporator. Same compressor could be used but it would be producing higher pressure than it was used to.

If the system is dry (no pressure), you would need to do a vacuum. If there is pressure, then it might not be needed.

 

Basically I have seen people do this and it worked fine. I do recommend changing the compressor, new oil, orifice tube, drier receiver, txv and all o-rings then pull a vacuum and weigh in the charge.

If in fact you still have positive pressure left in your system, then I personally would use a drop in like Freeze 12 or better yet find some R-12 to "top off" what you have and see how long it holds a charge. If it leaks out before winter then you should find the leak(s) and fix them. Again vacuum is ALWAYS best if you recover the refrigerant and open the system to atmospheric pressure for any repairs. I hope this helps.
Scot

 

If it already has a bit of R134a you CANNOT "top off" with R-12 or Freeze-12. You would be making a whole new chemicl composition of who knows what thermal dynamic properties. Find the leak, repair and re-charge as per standard refrigeration practices. Better yet take it to a professional. Some things are not DYI. This is one of them.

Mike

35 year refrigeration technician.

 

Most of the older AC hoses are not compatible with R134 and a Barrier type hose is needed. Otherwise, the 134 will leak through the original hose over time.

 

From all that I have read, the R-134 switch on POA-equipped cars will work MUCH better if done properly, including flushing the system, changing the receiver / dryer, and recalibrating the POA valve, but many people seem to have functional A/C after simply letting the R-12 out and filling the system with 134.

Since the damage has already been done by the PO, I'd say fill 'er up with 134, which isn't too expensive yet, and see how it works. If it leaks down sooner than you think it should, then try to find the leak.
If you've got to open the system to fix the leak, or if it just won't cool right, even with a full charge, THEN replace the parts the PO should have replaced in the first place.

- Eric