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Completely original 72 Cutlass Supreme Convertible AC System. Only ever replaced the relay melter thingy/whatever that melted once.
About 20 years ago, the system got evacuated, some ester and O ring conditioner and r134a added - no drier or anything. Been cold and nice until about a year or two ago. If using for long, the compressor wants to start to seize up and squeal the belt. I stopped using the AC, but it will turn on and get cold for short bursts. I figure that the compressor is getting old/weak? I added more oil today just to see if that will fix it, but I do not have any hopes...
Was going to order a reman A6 and drier and replace them, evac the system and refill with oil and r134a. The system does not currently leak, so I am wary of cracking anything else open, but I will if it is extremely recommended.
Even a few years ago, it put out air in the 50s on a day in the 90s with very little humidity. I am assuming that everything else is working OK, but is this a bad idea? Guess that I need to do the POA for r134 while I have it all apart?
50 degree vent temps with 90 ambient seems too high; I recall mine put out mid-30s with 90 ambient temps. That was R12 so R134A would be a bit higher, but 50 sounds too high to me.
I would put gauges on it and check the high and low side pressures to see if they are in spec. Could be the refrigerant charge is not correct. This could also give an indication of the compressor’s health.
This is a lot cheaper that buying and installing parts with no idea if those parts are even bad and if replacing them will change anything.
Last edited by Fun71; June 26th, 2024 at 04:54 PM.
I would put gauges on it and check the high and low side pressures to see if they are in spec. Could be the refrigerant charge is not correct. This could also give an indication of the compressor’s health.
x2 on putting some gauges on it first to get the readings.
Oil seemed to help because I got the compressor to run for long enough. 32 on the low and 150 on the high... might need a bit more. Started to pour rain, so done for the day.
I don't know, those readings seem w/in range to me. Did you perform a static pressure reading? Static pressure on both low side & high side should be almost equivalent to ambient temperature.
Oil seemed to help because I got the compressor to run for long enough. 32 on the low and 150 on the high... might need a bit more. Started to pour rain, so done for the day.
It is cooling something... line is frosty!
That frosty line is an indication of a problem. It's indicative of a restriction in that valve.
It's acting like an expansion valve, causing the line downstream to frost up.
It shouldn't be like that.
Last edited by Charlie Jones; June 26th, 2024 at 07:55 PM.
If I have to replace the POA, then no sense in putting it all back together with the old compressor that I know is suspect... so compressor, drier and expansion valve coming soon.
Guess I will add the valve onto the replacement list. I might have a 15-51 in a box - I have a vague recollection of seeing one that was not used about 20 years ago. If I have to buy/order a POA, do the replacements that turn the compressor on/off work OK in the long run? Seems like a risk since these clutches were not made to cycle that much, but I have no experience and just a hunch. I can have the old POA rebuilt, I guess.
What about hoses? Some say no need and other say, absolutely.
If it helps, the system has never been open. Has had refrigerant in it the whole time.
Suggestion: Call this number and speak w/ an expert technician who can professionally assist you w/ your questions. I rebuilt my R12>R134A system on my 1971 CS convertible and they were outstanding >>> (817) 531-2665
I used an updated POA exactly as the one on this site - worked flawlessly. Tell them what you are working with. They don't try to up sell, they want to sell exactly what's required for your system. Good Luck!
If I have to replace the POA, then no sense in putting it all back together with the old compressor that I know is suspect... so compressor, drier and expansion valve coming soon.
Guess I will add the valve onto the replacement list. I might have a 15-51 in a box - I have a vague recollection of seeing one that was not used about 20 years ago. If I have to buy/order a POA, do the replacements that turn the compressor on/off work OK in the long run? Seems like a risk since these clutches were not made to cycle that much, but I have no experience and just a hunch. I can have the old POA rebuilt, I guess.
What about hoses? Some say no need and other say, absolutely.
If it helps, the system has never been open. Has had refrigerant in it the whole time.
I don't think your compressor is that bad by the pressures posted, but, get a replacement anyway if it makes you feel good.
A new dryer is a must if the system is opened.
The collective experiences of this forum mostly do not favor the cycling clutch POA replacements for the reason you stated.
Some place like Old Air Products should be able to repair that POA valve.
The one hose that I can see in the pics doesn't look like factory crimp.
So the hoses may have been replaced when it was converted to R-134 twenty years ago .
That frosty line is an indication of a problem. It's indicative of a restriction in that valve.
It's acting like an expansion valve, causing the line downstream to frost up.
It shouldn't be like that.
Frost can form on the suction line when that valve is functioning normally too. That valve, the Pilot Operated Absolute/Suction Throttling Valve - POA/STV, lives to keep the evaporator pressure (and temperature) from going lower than about 30 psi (about 30 degrees F.). Doing this prevents the condensed water vapor on the evaporator fins from freezing.
If the heat load on the evaporator is low because of a low fan speed, low humidity, or low ambient temperature for instance, the POA valve will modulate to "throttle" or reduce refrigerant flow out of the evaporator. Under this condition it is acting like an expansion valve (creating a restriction and pressure drop) causing frost to form.
Other tests need to be done before concluding the valve is bad or the system is malfunctioning.
Put in 12 ounces. Got cold at idle, but at RPM it was warm. Frosty line mostly just damp. Guages at 32/175 at idle and slightly less at RPM.
Put in another 12 ounces and cold both at idle and RPM. Went ahead with 2 more ounces and some dye.
Idle is 32/250 and RPM is 32/215-220, or so. My gauges are plenty old and might not be all that accurate.
Max AC is not blowing any better than Normal AC, so looks like I have something else to fix. I hate vacuum and dash stuff. Any known issues with this that I can start with? If I understand the pressures and stuff, more air through the evaporator means colder air. Right now, 47 on a 97 degree day... so not bad.
If it leaks, I will take it all apart and flush, do new O rings, drier, adjust the POA valve for r134 and recharge with a known amount. If not, then I will just wait until it leaks.
Appears POA was acting as an expansion valve on a low charge?
I am sure that I am not done, but I appreciate all of the responses so far.
Also forgot how much more heat the AC puts out... temp up 10 degrees. Under 200 on a 97 degree day, so OK. Also had to turn the idle up a bit. ...things that you forget after a few years.
You can look on-line to find a pressure chart for r-134a to see what it should be 134 pressures are much more sensitive to the outside temps than r12 so using a chart will help get the correct refrigerant charge.
I will also second that these do not look like factory hose crimps so your system may have been repaired in the past. Was the condensor replaced maybe?
Last edited by cjsdad; June 30th, 2024 at 09:36 AM.
AC ticket is closed for now. Took off the inner fender and the blower motor wheel was covered in old hood blanket (or something). Evaporator compartment jammed full with maybe 10% of the coils showing. Got the end of a small shop vac down the chute and used the other holes for compressed air. Separated the two halves and took the housing away from the firewall for a bit more access. Got it about 90% clean.
This must have happened before me. I got the car in 1998 and it had new interior and I put a new hood blanket on not too much after this. I am amazed that I never smelled anything.
It is only about 85 degrees here today, but took a 30 minute test drive and I could not run the air on Max without freezing my crotch off. Happy.
Schrader valve on the low side has a slight leak, so put a metal cap on it for now. Will take all of this apart when I have to open up the system and clean it better.
Pressures changed a bit with the evaporator working well. I think that I have it slightly overfilled. I will check it in a few weeks or a month and see how everything looks.
Car fought me a bit... Edelbrock fuel pump quit and I put on a new fuel pump on the side of the road. Just going to use Napa ones from now on - keep a spare with me. The cheap ones seem to last just as long, draw less load and can change them out with a few wire nuts, screwdriver and wrench until you get home. She should be happy now with one less mouse nest in her.
June 26th, 2024, 04:34 PM
