Refrigerant Type: R-12
I need to replace the expansion valve on my R-12 A/C system. However I can only buy an expansion valve with R-134a. There are parts sellers advertising they sell R-12 expansion valves however I just bought one and when I received it, there is R-134a printed right on the valve. So it seems I can only buy R-134a valves.
Can you use expansion valves that contain R-134a in a R-12 system??? Note: I AM refilling the system with R-12. The condensor design on my car does NOT permit R-134a.
Edited: Tue April 27, 2010 at 10:06 AM by mattd860
Newly made TXVs are suitable for either refrigerant. The thermal properties of the two under evaporator conditions are close enough that it is not necessary to recalibrate the valve.
So I shouldn't lose efficiency by using an R-134a TXV with R-12 refrigerant?? If there is efficiency loss, will I feel it in the air or will it be un-noticeable?
Do expansion valves contain specific refrigerant that expand and contract the valve? Or is it mercury and a spring?
After overhauling my entire A/C system and filling with genuine R12, I now have Luke-Warm A/C which I what I had before. Needless to say I'm pretty upset. When Idling, the a/c blows around 55ÃÂ°F and when driving it will drop to 45ÃÂ°. The culprit must be that stupid R134a expansion valve. I'm going to bring it to an A/C shop this week and have them recover the R12 and then refill with their own R12 just in case I somehow got a little air into the system. If the temps are still terrible I'm going to flush out the mineral oil and try R134a since I have the R134a valve. I'm also going to call all the resellers of so-called "R12 Compatible" expansion valves and give them an ear-full.
Just to rule a few things out here's my procedure for refilling the system.
-First I replaced the following components with brand new genuine oem parts: Condenser, condenser fan, evaporator, TXV (R134a - can't get R12 valves anymore), lines, dryer/accumulator, and o-rings. I also replaced my compressor with a professionally rebuilt one.
-Then I fill the system with 6.75oz (BMW specified system capacity) 500wt mineral oil
-Next I pulled a vacuum Tuesday May 25th and let it sit until Thursday. After seeing the system held a vacuum, I opened the system and pulled a vacuum about 4 more times between Thursday and today (Sunday)
-This afternoon during 85ÃÂ°F weather, I filled just shy of 3 cans of R12 to equal about 2.1lbs of refrigerant.
I own a Mastercool Manifold set and a Mastercool 3cfm vacuum pump - both high quality items.
If anybody sees any blatant errors in my procedure or anything else, please let me know. Thanks
When you switched cans of R12, did you purge the hose connected to the r12? Also, spray the condenser with q water hose. See if the high side drops . If so, you may have an airflow problem across the condenser. That would explain why the temps drop while driving.
What's your high pressure and your low pressure at 2000rpm after 10 minutes of running?
I also don't think the expansion valve is the issue. What/who/how diagnosed the expansion valve as the culprit in the first place? Check for operation of fans (fan clutch), AC clutch slipping, etc.
Yes, I purged the lines when switching cans. I just cracked the hose fitting for a second. Maybe I didn't purge long enough?
I'll try the water over the condenser later today. I have the stock BMW grille and a brand new oem fan so I doubt it's an air flow problem.
It seems like when rpms increase, the compressor compresses the refrigerant more quicker and more efficiently. With I rev up the engine to 1500+ rpm while the car is stopped, the temps also drop. I don't necessarily have to be moving to the temps to drop although I do reach peak performance when I am moving. I suspect it's the lousy R134a valve that requiring higher than normal R12 pressure from the compressor. Make sense?
55ÃÂº at idle and 45ÃÂº at 1500 rpm? I don't think you have a problem at all.
When the car idles at 800rpm, the air temp is 70ÃÂ°F when the interior fan is on max and it does NOT cool the cabin (yesterday temps were 80ÃÂ°F). There is a problem.
When I'm stuck in gridlock traffic on an 85ÃÂ°F day I'll have better cooling by just rolling down the windows.
It's an '89 euro car. That IS the expected A/C performance. A "gentle cooling" that will allow you to run the highway without wind buffeting from the open windows...
Blaming the TXV in this case is misguided. The first thing you need to do is post pressures. If the compressor is weak, it will show up during a full load test:
Doors open, Cabin fan on highest speed.
Raise engine rpm to 2000 Maintain engine speed for 5 minutes minimum
With engine speed still @ 2000 rpm, record High & Low side pressures, Vent temperature & Ambient temperature.
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
" When Idling, the a/c blows around 55ÃÂ°F and when driving it will drop to 45ÃÂ°. "
The above quote was the reason I stated that you have no problem. I don't feel as if the TXV is the problem. You could check for a reheat problem by clamping off the heater hose. You can check the airflow across the condenser by misting the condemser witha water hose. You can also set up a 20 inch window box fan in front of the grill and see if cooling improves. Do you have a full charge of R12? Did you lose any while charging? Since you have a TXV, the charge is not too critical as the drier will storge some extra.
Does your replacement compressor have the same size clutch/pulley as the OEM?
If you have air in the system, the high side will be high. That is why pressures are needed to verify operation. If they recover the charge and air is in the system, the recovery tank will need to be at rest for at least 12 hours. Then read the temp of the cylinder tank and compare it to the pressure. Compare readings to a pressure /temp chart. Carefully bleed some vapor off and retest. It is a long process.
Once again, we can't help try to help you without the pressures and temps.
Low Side Pressure 70psi
High Side Pressure 280psi
At idle the low side reaches 90psi
I brought my car to an A/C shop today and they took the above readings before they recovered the R12, vacuumed the system, and refilled with new R12 (not the R12 they removed). When we restarted the A/C the gauges read EXACTLY as above!!
Immediately the tech (owner of the shop) asked me if I had an r134a expansion valve installed to which I answered yes. He said that is exactly my problem because the inlet of the r134a valve is not big enough for R12. So as a result the refrigerant cannot flood the evaporator. Needless to say - www.pelicanparts.com will not be selling any more r134a valves labeled "compatible with R12". The owner of the shop is going to find me a genuine R12 valve because I am unable to source one. All parts stores that I've called carry a R134a valve labeled compatible with R12 which is nonsense.
He says the fact that the bulb of the valve is filled with r134a makes no difference. It doesn't matter what it's filled with. What matters is the inlet opening of the valve which is no and cannot be the same for both refrigerants.
Edited: Fri June 04, 2010 at 7:00 PM by mattd860
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