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When I bought the car a few months ago, it had the factory AC, but no compressor or bracket. Bought a bracket from vintage air thinking it worked with the factory compressor. I was wrong. Bought the Sanden compressor that Vintage Air recommended and installed. Put the R134 conversion kit on and charged to 2.75lbs initially. Was just going off of pressures to determine the R134 amount. This was before I found out that Vintage suggested 1.8lbs...
Anyways, the issue is that on the interstate, the ac temp climbs to 90*... At idle, it drops back to 58*. Changed the worn out fan clutch and it didn't help. Need a direction to go so I'm not just throwing parts at it left and right. Anyone else had this issue?
What year and model car? Comfortron? Expansion valve replaced? Drier replaced? Evacuated before recharge? What are the pressures at idle?
Do the heater hoses both get hot when this occurs? On non-Olds cars a weak water control valve can be overcome by the pump pressure at higher RPM causing the heater core to get hot.
What year and model car? Comfortron? Expansion valve replaced? Drier replaced? Evacuated before recharge? What are the pressures at idle?
Do the heater hoses both get hot when this occurs? On non-Olds cars a weak water control valve can be overcome by the pump pressure at higher RPM causing the heater core to get hot.
58 degrees at idle also seems high.
1970 Cutlass 455. Factory AC with an updated compressor and R134.
Not sure what comfortron means? Didn't replace the expansion valve or the drier. Ran some AC cleaner through the lines/system and blew them out with shop air. Did an Evac and vacuum along with the leak test. Passed the 15 min leak test. Pressures at idle with 2.75lbs were 200/40 in an 85* shop. Pressures with 1.8lbs (which is what the vintage air site suggested) were 100/30 at 85* which seemed really low on the high side. Figured it was building too much head pressure with the 2.75lbs in it so that's when I started looking online and backed it down to 1.8lbs.
Not sure about the heater hoses both getting hot. I'll have to check them after the 25 mile trip home.
If this wasn't my daily, I wouldnt worry ab the AC as much. But a black car with black interior in Alabama during the summer months is a death sentence for whoever is in it lol...
If the heater hoses are hot it could just be the wrong valve, one version is normally open, the other is normally closed. A member did a write-up about the two valve version and their application.
Poa Valve? No I didn't. Just did the flush and the new compressor. The compressor acts like the clutch is slipping though. Started making noise a minute ago. Thinking I might need to warranty this one out, put a new one on there and wire in a high pressure switch for it to cycle.
A POA (Pilot Operated Absolute) valve is exceedingly finicky. R12 has a higher operating psi than R134; but, more importantly contamination of the POA valve is highly likely during a changeover & in particular in a system which is 70+ years old. I have a suspicion you're witnessing a contaminated POA valve.
Thinking I might need to warranty this one out, put a new one on there and wire in a high pressure switch for it to cycle.
You're adding one problem on top another.
R12 lubricant (mineral oil) is not compatible with R134 lubricant (PAG = Polyalkylene Glycol). Sounds like ethylene, or polyethylene glycol doesn't it? It is very, very similar but with significant amounts of Cl (Chlorine). R12 does not mix w/ R134. You could not have purged all the R12 from the system if you did not change the drier. R12 exists (pools) at the bottom of the drier - below the desiccant. If you didn't change the drier, you're now mixing R12 + R134. Eventually the compressor &/or the condenser are going belly up. The refrigerant circulates charged oil particles. In the case of mixing the two, you're introducing lubricant contamination into the entire system. Before you go sending out (back) you need to change both the drier & the POA.
You're adding one problem on top another.
R12 lubricant (mineral oil) is not compatible with R134 lubricant (PAG = Polyalkylene Glycol). Sounds like ethylene, or polyethylene glycol doesn't it? It is very, very similar but with significant amounts of Cl (Chlorine). R12 does not mix w/ R134. You could not have purged all the R12 from the system if you did not change the drier. R12 exists (pools) at the bottom of the drier - below the desiccant. If you didn't change the drier, you're now mixing R12 + R134. Eventually the compressor &/or the condenser are going belly up. The refrigerant circulates charged oil particles. In the case of mixing the two, you're introducing lubricant contamination into the entire system. Before you go sending out (back) you need to change both the drier & the POA.
Makes perfect sense! Greatly appreciate all the info guys. I'll install the new drier and POA valve before doing the new compressor and see if it helps. How much R134 are y'all putting in these systems? 1.8 lbs is what Vintage air said, but the pressures on the machine gauges were happier with the 2.75 lbs I had in there to begin with. Didn't know if it was building up too high though since that seemed like a lot for the size of the system. Hell, a newer Suburban with 3rd row air only holds 2.9lbs and this system seems like it would be a lot smaller.
Makes perfect sense! Greatly appreciate all the info guys. I'll install the new drier and POA valve before doing the new compressor and see if it helps. How much R134 are y'all putting in these systems? 1.8 lbs is what Vintage air said, but the pressures on the machine gauges were happier with the 2.75 lbs I had in there to begin with. Didn't know if it was building up too high though since that seemed like a lot for the size of the system. Hell, a newer Suburban with 3rd row air only holds 2.9lbs and this system seems like it would be a lot smaller.
I wish I could recall what my converted R12>R134 was in lbs - it's been ~5-6 years since I changed out a bad compressor w/ a rebuilt (and, yes I installed a new POA & drier) in my 1971 CS 350 cid. I recently (last summer) changed the AC compressor (and a million pulleys to accommodate the new serpentine belt) in my 2003 Ford F250 diesel and I couldn't tell you how many lbs I used on that one. I believe you're going to be impressed changing out the POA & drier though. There really is a need to remove as much contaminant as you can in the system and those two components really do require changing when converting on these old beasts.
How much R134 are y'all putting in these systems? 1.8 lbs is what Vintage air said, but the pressures on the machine gauges were happier with the 2.75 lbs I had in there to begin with.
I disagree - you said the low side was at 40, which is fairly high - low 30s is where it should be, and is where you said it was with VA's recommended charge amount.
Norm, I suspect any residual R12 boiled out when the system was open, and definitely during the 30" vacuum operation.
There is only a difference of 6 degrees boiling point between R12 & R134. More importantly, the drier desiccant in an R12 is different than the drier desiccant in an R134; additionally, molecular size alone makes R12 (mineral oil) far much larger molecules than PAG. At any rate, you should always change the drier any time you change over from R12>R134 unless you like less lubrication and prefer sludge.
I agree with you on replacing the drier and using the appropriate oil; I was referring to the statement you made below. Any pooling of R12 would evaporate rapidly when the system was opened, and also when vacuum was pulled.
Originally Posted by Vintage Chief
You could not have purged all the R12 from the system if you did not change the drier. R12 exists (pools) at the bottom of the drier - below the desiccant.
Originally Posted by Vintage Chief
the drier desiccant in an R12 is different than the drier desiccant in an R134;
The drier I bought for my car had a label stating it was compatible with either R12 or R134A refrigerants.
Kenneth - OK. I'll concede. Valid point(s). Ya know, in my head I'm actually considering the manner in which the actual oil is dispersed throughout the system - which is via the compressed refrigerant. So, I was rather mixing apples w/ oranges here. The actual refrigerants themselves would evaporate, you're right; but, the oil(s) would remain. I have my days.
I disagree - you said the low side was at 40, which is fairly high - low 30s is where it should be, and is where you said it was with VA's recommended charge amount.
100 psi on the high side seems awful low though doesn't it? In an 85*-95* shop?
Yes, that does seem low, but the weight charge is what VA recommended. I am unfamiliar with their compressor, so I dunno.
The pressure should be checked with the engine above idle speed (1500 or more RPM) and with a strong fan blowing into the radiator/condenser. If checked at idle, the pressures will not be accurate.
If the charge is too low, the system could be freezing up at highway speeds, which then causes the vent temperature to climb.
As previously stated, R12 mineral oil and R134a PAG oil are not compatible; always replace the drier when opening the AC system, it's impossible to completely flush the drier when converting refrigerants. Here are a few other things often overlooked when doing an R12 to R143a conversion. The stock tube and fin condenser used with R12 does not have enough surface area to extract the heat of R143a. For best performance, the condenser should be replaced with parallel flow style condenser. There are universal condensers that will require custom hoses, but you can also now by a stock looking condenser designed to work with R1434a. you're If keeping the factory AC system, you need to calibrate the POA valve to bypass at a different pressure, this prevents the evaporator from freezing. The POA valve is set by the factory at 29.5psi for R12; recalibrate the POA for R134a to 27.5psi, this will help the converted system achieve the best cooling without freezing up. There is a small set screw in the end of the POA that sets the bypass pressure point. You can do this yourself using shop air and pressure gauge or there are several AC vendors that will recalibrate your POA. There is(was) a guy on classicoldsmobile.com named "banny" that will provide this service.
Rodney, that's good information with one clarification. The recalibration of the POA valve is to get the temperature at the evaporator a bit lower due to R134A not cooling as well as R12. The lower pressure point results in lower evaporator temperature before the valve restricts the refrigerant flow. Think of it the same as reducing the low pressure trip point on a newer system that has a low pressure cutoff switch - it allows the evaporator temperature do drop several degrees cooler before the system cycles off.
As previously stated, R12 mineral oil and R134a PAG oil are not compatible; always replace the drier when opening the AC system, it's impossible to completely flush the drier when converting refrigerants. Here are a few other things often overlooked when doing an R12 to R143a conversion. The stock tube and fin condenser used with R12 does not have enough surface area to extract the heat of R143a. For best performance, the condenser should be replaced with parallel flow style condenser. There are universal condensers that will require custom hoses, but you can also now by a stock looking condenser designed to work with R1434a. you're If keeping the factory AC system, you need to calibrate the POA valve to bypass at a different pressure, this prevents the evaporator from freezing. The POA valve is set by the factory at 29.5psi for R12; recalibrate the POA for R134a to 27.5psi, this will help the converted system achieve the best cooling without freezing up. There is a small set screw in the end of the POA that sets the bypass pressure point. You can do this yourself using shop air and pressure gauge or there are several AC vendors that will recalibrate your POA. There is(was) a guy on classicoldsmobile.com named "banny" that will provide this service.
Rodney
Originally Posted by Fun71
Rodney, that's good information with one clarification. The recalibration of the POA valve is to get the temperature at the evaporator a bit lower due to R134A not cooling as well as R12. The lower pressure point results in lower evaporator temperature before the valve restricts the refrigerant flow. Think of it the same as reducing the low pressure trip point on a newer system that has a low pressure cutoff switch - it allows the evaporator temperature do drop several degrees cooler before the system cycles off.
Someone else did the changeover from R12>R134 on my '71 CS (and, I don't know when that happened). Purchased the car w/ a bad compressor and bad core. Installed rebuilt compressor, new core and new drier - still marginal cold air. Examined the POA valve & screw hoping to adjust w/ no success, then pulled the POA, then replaced the literally filthy POA and BAM! Air colder than an ice maker (not really). Bottom line - failed POA valve.
Someone else did the changeover from R12>R134 on my '71 CS (and, I don't know when that happened). Purchased the car w/ a bad compressor and bad core. Installed rebuilt compressor, new core and new drier - still marginal cold air. Examined the POA valve & screw hoping to adjust w/ no success, then pulled the POA, then replaced the literally filthy POA and BAM! Air colder than an ice maker (not really). Bottom line - failed POA valve.
Picked the drier up yesterday. Looks like I'll be snatching the POAV off and adjusting it. If it works, great, if not, I'll just have to order a new one...
Good on you changing out the drier. I sincerely wish you the best regarding the POA but remain modestly skeptical. Just a kinda recap so we're on the same page. You can & most likely have reviewed the function(s) of the POA valve.
As Kenneth & I were discussing R12 vs R134 it may not have been articulated clearly in the discussion - let's make sure these points are understood:
(1) The refrigerants themselves BOIL at around -21.6°F (R12) & -15.34°F (R134). When you open the system, yeah they're both going to evaporate (boil off) quickly; however,
(2) It isn't the actual refrigerants which muck up the system(s), instead it's the oils used in each system are very dissimilar. The lubricating oil is circulated through the system by the refrigerant as charged particles which adhere(s) to the refrigerant(s). Basically mineral oil (R12) is not miscible (does not mix) w/ PAG (Polyalkylene Glycol) - very similar but not same as antifreeze (Polyethylene &/or Ethylene) glycol. Glycol is NOT soluble (miscible) in mineral oil. I found a great statement regarding the non-mixing of mineral oil w/ glycol:
The addition of glycol can cause oil to thicken and as a result, interrupting its flow through the engine. The resulting thick gel that's formed by the addition of glycol is known as 'black mayonnaise' and can cause problems in parts of the engine that require a less viscous lubricant.
While that statement (above) pertains to mixing of glycol (antifreeze coolant) w/ engine oil, the exact same principle applies to the AC cooling system. Mixing of R12 (mineral) oil w/ R134 (PAG) creates black mayonnaise and that black mayonnaise has an excellent opportunity to disrupt the functioning of the POA valve. Below is a more or less typical POA valve - the needles &/or orifices are quite small. I wish you best of luck and hope you might be able to salvage the POA.
I converted my 72 Cutlass with this. It is a dryer for a 79 thru mid 80s cutlass. it replaces the POA and expansion valve with an orifice tube and a cycling switch. You will need the lines to from the dryer also. It has been on the car almost 5 years and works great. I agree that the stock condenser isn't efficient enough for R134. to help with this I added an electric fan (that I had laying around) to push air through the condenser. Also If you add ester oil to the mineral oil in the system the R134 is compatible with that.
A POA (Pilot Operated Absolute) valve is exceedingly finicky. R12 has a higher operating psi than R134; but, more importantly contamination of the POA valve is highly likely during a changeover & in particular in a system which is 70+ years old. I have a suspicion you're witnessing a contaminated POA valve.
Hooked the gauge up to the POA valve and shot air through it. Was popping open at 10 psi. I guess someone had been messing with it at one point. Set it to 27psi. Gonna flush the system again, put an electric fan in front of the condenser and see what happens. If this doesn't work, I'm going GS72's rout that he mentioned.
Last edited by GvEmHellBama; Jun 11, 2024 at 08:14 AM.
Put the air to the POA valve again today. Kept popping at 32 psi. Got some R12/R134 flush to run through it all as soon as I saw the results.
1) Is this a bad POA valve or could it just be gunked up from sitting for 30 years under a cover in a shop?
2) If it is in need of a rebuild, is there anyone in the site that still cuts them open, rebuilds the guts and welds them back?
3) GS72 suggested the 79-mid 80s conversion. I would be 1000% fine with it and prefer that if it worked with the 70 model. (Experience/advice is welcome)
4) Suggestions other than spending on a Vintage/Classic Air system???
I've got the V.A. bracket and Sanden compressor with the 134a conversion fittings mounted already. Have an electric fan for the condenser as well. Plus the new condenser mounted drier of course.
Just ab done in the shop with customer stuff for today. Going to get back on the AC stuff this afternoon and run the flush through the system. Is there a way to flush the POA valve? I was thinking of just spraying the port in the expansion valve and blowing air through it to push the solvent in the POA valve. Didn't know if anyone else had a better way?
Kenneth - Correct. Additionally, it is what the OP needs to update his system to R134A compatibility including pressure switch, wire harness and fitting to replace POA valve with ports for oil bleed line from evaporator, and equalizer tube from expansion valve. It performs flawlessly when upgrading (converting) R12A>R134A. As stated earlier, my bet is the current OEM POA valve (Post #24) is bad; and, the most likely reason it is bad is because the bellows have disintegrated, the needle valve is worn from oxidation/corrosion, the needle orifice is worn, the piston is most likely shot, & spring is most likely filled w/ snot & black mayonnaise & has lost its tension (if not rusted entirely) - not to mention the gunk/debris contained w/in.
Hmm. I had read here on the forums that the older compressors are not designed to be cycled on/off like the newer ones, and may not hold up over the long term. I have no experience with this, just passing on information.
I noted the OP said "updated compressor" but I don't know what that means.
Converting to R134A does not require a cycling clutch conversion such as this - many have just switched refrigerant and oil. Recalibrating the POA trip point is beneficial but not mandatory.
Hmm. I had read here on the forums that the older compressors are not designed to be cycled on/off like the newer ones, and may not hold up over the long term. I have no experience with this, just passing on information.
I noted the OP said "updated compressor" but I don't know what that means.
Converting to R134A does not require a cycling clutch conversion such as this - many have just switched refrigerant and oil. Recalibrating the POA trip point is beneficial but not mandatory.
There is nothing you wrote I disagree with. My scenario was nearly 100% identical to the OP's. I called Old Air Products, explained my situation; and, yes mine was a rebuilt OEM compressor I installed. How the conversation went was this. The OEM POA was designed for R12A & operates optimally for an R12A system. Save from the condenser, I replaced each AC component until I was baffled - which led to my Old Air Products call. I was informed their POA (update kit) was optimized to operate more efficiently under (within) a R134A system. It was suggested to me the OEM POA valves had a history of failure when converting R12A>R134A & in particular I was told it was the result of gunk/debris & breakdown of components w/in the OEM POA valve. In any case, they assured me it works, I ordered it, replaced the OEM POA with their updated POA and the car blew colder air than my truck - worked flawlessly. I suspect the OP should call Old Air Products and speak to one of their technicians?
