Hello, I've got a Riviera 67. Car was imported to Australia and had to be degassed before shipping. Once in Australia, I recharged the system with r134a (cannot buy R12 here) and compressor failed on high pressure on a hot day. After system failure, I then replaced condenser, new compressor, etc. Charged with r134a and it works "OK" only - not as cold as it should. I suppose the difference in performance is mostly due to original POA valve setpoint for R12 (~30-32 psig) being too high for using r134a. Questions: 1) Is it possible to safely adjust the car's original POA valve? If so, what pressure should the valve be set (I heard 20 and 26psig - quite a difference!). I am from Perth/WA and summer is 40degC+ and dry air. 2) Alternatively, I would consider recharging with Hydrocarbon refrigerant (i.e "M30" gas) and not adjusting the POA. Any experience with HC in this forum? I know and I am not interested (in principle) on either (a) serviced POA valves with setpoints adjusted to different gases (they are too expensive and mine works fine) and (b) "POA eliminator kits" - which is subpar solution in functionality to POA in my opinion.
I believe the POA valves are not adjustable. What companies like Old Air Products does is cut them open, make the necessary modifications and tig weld them back together
https://www.google.com/search?clien...adjustment#kpvalbx=__iXUYuzPC6WgqtsPzNeosAU10 Keep in mind, to have the system work as well as possible, not only does the POA need to be reset, or eliminated, you must also replace the drier and change the oil in the compressor.. Usually you can make it thru a season without the barrier hoses, but having to recharge once a year will be normal. The 134A will go right thru the standard R-12 hoses and fitting o-rings after a while. If you have the hose making tools, then just buy the correct size rubber line and ferrules and replace the rubber in your current hoses, and add the 124A safe O rings on the joints. JW
Most of them are adjustable. I think most ended up being about a 1/4 turn counterclockwise. If you do not want to set up a gauge or send it out.
Yes, POA valves are easily adjustable. There are several videos on youtube that show you how to do this. You may want to try R152A, which is an industrial refrigerant commonly used in keyboard duster sprays. Many people have had success using it in old R12 systems. You will find many videos on this on youtube as well. It is cheap and widely available all over. Many people use hydrocarbon refrigerants (such as straight propane). There are obvious flammability concerns, so use your own judgement.
My concern it that in adjusting the POA valve "about 1/4 turn" (which translates to a pressure setpoint that I do not know the value - and the reason for my original enquire that still remains), I end damaging the valve that currently works well. The M30 gas is a mix HCs (propane / butane (?)) at rations different to typical "LPG". I understand this HC mix was designed to perform with similar characteristics as R12 and I've heard it works great - i.e. freeze cold, like R12 on 70's A6 compressors, could be a drop in retrofit solution, it lower compressor head pressure, uses mineral oil, large molecular size leading to lesser leakage rate, etc - all the good stuff. The "flammability risk" in the context of an automotive air con system does not concern me - I think the risk perception is blown out of of proportion in my opinion. Recent air con systems are charged with new "1234" gas in lieu of R134, and the former is called "somewhat flammable". I bet they would be rather "flammable indeed" in a leak under pressure with oil mixed. Furthermore, that current Air con system designs did not change in construction to accommodate the so-called "fire hazard risk" of large leak AND Ignition source AND people in the cabin AND engine firewall collapse AND .... I guess some O-rings were not replaced during new hoses / compressor retrofit done last year - possibly the reason why R134 leaked in one year (aftermarket new compressor seals too?). I will open the system again, change balance of old O-rings to a R134 spec (just in case, for future compatibility) and recharge with M30. I will report performance to forum once this is done. Cheers/Alex
Don't forget to install a more efficient condenser which would have more numerous and smaller tubing and more and finer cooling fins. For some strange reason no one mentions this.
Ok - So charged the aircon with the HC gas (https://hychill.com.au/products/minus-30), "not scientifically" by any means as I cannot relate to what an equivelent charge weight would be since compressor / condenser were replace, etc. I kept checking the outlet temperature while slowly adding some gas with an eye on hi/low pressures, subcooling/superheating of inlets/outlets, etc. The overall performance? My finger almost freeze out of the vents - it is awesome, like the old R12 performance, loved it! I won't go back to R134, that is one thing for sure...
Why is no one mentioning adjusting the expansion valve? There's a brass nut in the valve (looking from underneath) that has a hex hole for an Allen wrench. Turn that in while counting the turns, take that number and divide it in half and turn it out that amount. From the factory, they are usually 7 to 10 turns, so, it will end up 3.5 to 5 turns. I ran my 72 C-10 like this for 7 years without a problem with stock evaporator and condenser. It also helps to get more air flow over the condenser by sealing the radiator to the core support and sealing the condenser to the core support. I did this using 1/2" pipe insulation. Also make sure the shroud is tight against the radiator.
Since a molecule of R134 is smaller then a molecule of R12 the restriction at the expansion valve must be increased to get the correct pressure differential across the expansion valve. This also helps to bring the low side pressure down. On systems without POA valves, only the expansion valve gets adjusted or replaced. On fixed orifice systems (78 and up), the orifice tube gets replaced by a variable orifice tube which is an expansion valve. R134 needs to be squeezed more.
