still having issues with both chevelles ac. HAve added post at ackits and still havent figured it out and my ac guy is stumped too
chevelle1- evaporator freezing up...High side is reading around 100. Low side seems normal. Have replaced expansion valve and no difference. I have a POA repalcement tube so there shouldnt be issues there. The ac was fine until i got it back from body shop and all my r12 was gone. HAve put r12 back in and no leaks. hmm. what else could it be?? It blows warm

chevelle2- High and low seem to be reading normal. blows mildly cool and then blows warm and so on. Only blows about 15 degrees cooler than outside air at best. Its over 90 now so doesnt help much. Everything in that system is new or rebuilt. Has a rebuilt POA and r12

If anyone has any ideas please chime in. My ac guy has gotten frustrated too

Sounds like #1 needs more refrigerant.
100 PSI (I assume not 100 degrees) is way too low
what is the back pressure reading?
how is the air flow?
not enough air passing through the evaporator will cause "frost up"

Might be time to look for another A/C tech.

The exact amount of refrig. is in both cars. believe me..i had to pay $30 a pound. Could the expansion valves im getting not be calibrated? It worked fine until it went into the body shop.

Does your poa replacement tube have a cycling switch on it? If so disconnect the wires and unscrew the switch from the tube(should have schrader valve so you don't loose R12) then plug wires back up and see if the compressor still runs. If it does then the cycling switch is not working allowing it to freeze. What is the low side pressure? High side should be around 250# At what point on the evaporator do you see frost. What did the body shop repair

Blaster,

Was the POA tube on the car when it went to the body shop? If not, that could be contributing to the problem, depending on the set cut-off pressure. Either way, if it was me, I'd eliminate the POA "eliminator" tube and return to a real POA. With the original style compressor (A6), and a retro eliminator kit, ... that compressor will be cycling too frequently. The A6 clutch wasn't designed for such a system, from what I've heard. Can't beat a properly functioning POA.

Missing all the refrigerant, and no detectable leaks makes me wonder. Was the compressor possibly removed to "get it out of the way" and then re-installed, at the body shop? If so, and the system was left open, it could have moisture or what ever, in it. I'd consider flushing the system ... installing a real POA, evacuating, and charging refrigerant by weight.

If both your cars use the same system, compare the air flow. If the same, chances are the problem is not in that area. If a noticable difference, ..time to investigate. Like Dean mentioned, ... low freon or inadequate air flow would be the areas to first consider. If the system had been functioning with the POA eliminator, then that's probably not causing the freezing, but it won't perform as well as it was originally designed to with it.

What's the ac back ground on Chevelle 2? Has it ever worked correctly with the new parts? What are the exact pressures? I'm no expert at this auto ac stuff, but I've been sucessfull at it, working on my own vehicles. Having been a non-auto ac tech also helps.

Car 1- right before I took it to the shop I had topped off the ac with a pound of freon. Worked great. It seems to leak about a pound a yr. I asked the guy to turn it on now and then when it was in the shop just to keep things moving. I doubt he did and its just odd how I had no freon left when I got the car back after 6 months. He was a shady guy as it was. When I got the car back I filled it back up and it worked but after a couple minutes the evap. would freeze up annd I would have to turn it off for a minute to defrost it.Now the evap still freezes up but it wont blow cold ever. I thought the pressure switch on the pOA replacement tube was bad becuase trying to adjust it , it would either cycle constantly or not at all. Replaced the switch and it still does it. Theres no in between. The replacement tube has been on there 8 yrs and works great. Im not paying $300 on ebay for a new POA. I figured the replacement tube would at least rid me of the typical problems they have.

Car 2- I got the car in 2002 and the air hadnt worked in 20 yrs. I restored the car from ground up and replaced all of the ac parts.
compressor-rebuilt
expansion valve-new
hoses-new
condensor-new
dryer-new
POA- rebuilt from classic auto air in tampa
evaporator-pressure tested it and held
r-12

All pressures almost perfect. Just blows mildly cool air

The "one pound a year" leak, might have gotten bigger, and let all the R-12 escape. As I suggested, ... evacuate with a vacuum pump. If it will not pull down and hold, then the leak is big enough to suck air into the system. Time to locate and fix. If it holds, charge by weight. My 70's hold 3.75 lbs of 12. Use gauges to monitor system.

My 1970 factory manual shows these relationships as examples with suction @ 28 -31 psi.

Air temp entering condenser / Compressor head pressure / Discharge air temp

70 . . . . . . . . . . . . . . . . . . . . . . 135-145 . . . . . . . . . . . . . 37-40
80 . . . . . . . . . . . . . . . . . . . . . . . 165-175 . . . . . . . . . . . . 38-41
90 . . . . . . . . . . . . . . . . . . . . . . . 190-200 . . . . . . . . . . . . . 40-43
100 . . . . . . . . . . . . . . . . . . . . . . . 210-220 . . . . . . . . . . . . . 44-47
110 . . . . . . . . . . . . . . . . . . . . . . . 230-240 . . . . . . . . . . . . . 46-49
120 . . . . . . . . . . . . . . . . . . . . . . . 255-265 . . . . . . . . . . . . . 49-52

Car 2. If the "fresh air" damper, in the cowl, passenger side, ... is staying open or not completely sealing, you could be pulling additional hot outside air , which would put more load on the system. It's just one more thing to check. If the pressures are near perfect, as you've said, ....that interior should get plain "chilly". Before my EC's original compressor went south, a while back, ... that's how mine was working. Hope you can both systems performing correctly.

This may have nothing to do with the problem. I replaced the evaporator on my one owner 70. Vac & Charge with 12 fire it up and it started to freeze up, So I got some of the old insulation to cover up the sensing tube on the top of the evap. Now it works OK. Do you have the ins. on the bulb. Mine is all org. 70 stuff that came with it except the new evaporator. Dont get excited just be COOL !!
Bob

You can't fix an ac system without looking at the guages attached to both the low side and the high side. I agree with brimac those poa replacement tubes are not the best. That A6 compressor clutch will not do too well cycling. Anyway with the car at idle, fan on high blow, cycling switch not cycling what are your low and high side pressures after running about 3 minutes. Again at what place on the system does the ice begin to form. Also is there a good flow of air out of the vents. I fix ac for a living so lets fix this one>

HMMmmm, my 79 GMC van had an A6 compressor with the CCOT system, the clutch handled it well. Different clutch?

FIRST YEAR FOR CCOT A6 was around 78 and I believe the last year for CCOT A6 was around 1980. Replaced many cycling A6s with clutch slung apart. Cadillac, buick, chevy pickup, chevy van. R4 does use a different clutch. Older lincolns used A6 but compressor ran all the time on auto and never cycled. Also used POA valve. I have fixed many GMs with POA valve. I have a tool to test the valve. If it is bad I replace it with a rebuilt, recalibrated valve from classic out of Fla. A properly working poa system will cool well but the CCOT system is an improvement from a reliability standpoint.

The exact amount of refrig. is in both cars.

How can you know that?

#1
Any bubbles in the site glass?
What is the low side pressure.
I would dump in some refrigerant and get the head pressure up to 250 -275 psi (if it's still 90*)

Both systems have the exact amount of refrigerant. 3.75pounds. No bubbles in sight glasses.

Car #1-The car with the POA replacement tube has worked 8 yrs with it just fine. As long as the system was charged i never really noticed the cycling. If it got a little low then i could hear it going on and off. Even with it fully charged the high side reads only around 90. Low side reads around 40. Its warm now in fla. The evaporator will freeze up quick when the system is on but im never even getting cool air even at first. A few weeks ago when I had charged the system back up it was running cool at first until the evap. froze up and I woiuld turn it off and let it thaw and then could turn it back on for a minute, and so on. Now theres never cool air. I have put a vacuum on it and it doesnt show any leak down even though there must be small one since im losing about a pound a year.Maybe sitting at the body shop without running made it leak out?maybe the body shop guy took it? The system should still be working though

Car #2- high pressure was around 200. low around 40. Evap is cold. Full charge and no bubbles. Rebuilt poa tested and seems to be working like it should.

According to my 66 chassis service manual:
1) Loose expansion valve bulb will result in high low side pressure and poor cooling;
2) exp valve stuck open: noisy compressor and no cooling, evap. freeze up;
3) exp valve stuck closed or plugged inlet screen: Very low suction pressure and no cooling;
4) Poorly located power element bulb: normal pressure and poor cooling.

I will have to look into some of the exp. valve issues then. On car #1 ive replaced it with a new one 2 times and its still doing it. I ordered an ac delco one just to eliminate discount auto parts exp. valves as the possible culprit
Are there inlet screens anywhere in the 72's?
On car #1 i have a very old a-6 on it. Its somewhat noisy but has good suction. an issue there possibly?

I checked on Rock Auto and they have the same inlet screen for the expansion valve for both 66 and 72 Chevelles.

Refer back to my earlier post. Looks like it could be items 1 or 2 for Chevelle #1 and item 4 for Chevelle #2. The low high side pressure on Chevelle #1 with a full charge of r12 could be due to a bad compressor because I am not sure if a stuck open exp valve can drop the high side pressure from 190-200 psi (where it should be at 90 deg ambient) down to 100. Definitely check the exp valve bulb attachment and insulation (as Bob said above) on Chevelle #2. You definitely need the inlet screen to the expansion valves. Hope this helps.

Just had another thought, concerning #2. Is by chance ..the vacuum controlled heater valve, (on right inner fender) stuck open.? If so, a hot heater core would add noticebly to the heat load, and higher vent temps.

Car#1 Is the evap icing up on the inlet pipe right after the x valve or is the larger suction pipe that exits the evaporator freezing up first. If you have a blockage ie; inlet screen, closed x valve trash from bad compressor and some freon is making it through but not enough it will cause the freezing and because the freon volume is not enough on the suction side the compressor is starving and cannot create compression or pressure on the high side. At 40 psi on the low side if there is enough volume the evap should not freeze. Look for the spot that freezes first and you will find your blockage!

A plugged TX valve inlet screen causes very low suction pressure (vacuum) and low head pressure .

High suction pressure and low head pressure is an indication of bad valves in the compressor. (or compressor not running)

A partially plugged screen or a valve that is not opening far enough or A PARTIALLY STOPPED UP FILTER DRIER can allow 40 psi on the low side but the lack of volume will keep the high side low because the compressor does not have enough gas to compress.
However I have replaced A6s with these symptoms and fixed the problem.

ANY restriction on the low side will result in lower suction pressure and head pressure.
40 psi is not low for R-12.

Car #1- I think i might replace the compressor since I have no idea how old it is. Ive had the car 8 yrs and the ac didnt run for yrs before I had it. Aso need to replace the drier since its been a while since ive replaced that along with trying another exp valve. I will look for a screen of some sort while im at it. The area that is freezing up is the tube that comes out from the bottom of the evaporator. The tube on top stays warm. should i spend big $ and replace that too?

Car #2- since evrything is brand new or rebuilt im not sure where to start except replace exp valve. I have checked the heater door and even pinced off the heater hoses. The evaporator tubes just arent getting very cool so I think its nore than just a vacuum door.

The expansion valve is probably becoming restricted by junk from a bad compressor or drier and if the compressor cannot create enough suction because it is not in good working order then the lowside is going to show normal ie: 40 psi if the compressor was working better it might pull the low side into a vacuum. To do a good job replacing that compressor you must make sure you have removed all of the crud from the evaporator, hoses, and condenser by foward flushing and back flushing each item individually. You can have this done by an AC shop that has the proper flush and flushing device. Replace the drier and the expansion valve. Be sure and use a new ac delco compressor I think it is # 15-2227. It should come with 10oz of mineral oil for use with R12. We always open the drain on the compressor and pour out the oil to make sure there is 10ozs of oil then refill the compressor. After replacing the parts and orings pull a 2hr vacuum to make sure all of the flush is boiled out. Then see if it holds that vacuum for an hour. If it does I would put 1oz of dye and a full charge of freon. If it doesnot hold a vacuum you need to find the leak or you will be out of expensive freon pretty soon. Good Luck

Im going to order the parts today.I will get back when I get it done. Thanks for all the help. Couldnt do it without all the guys from Team Chevelle!

http://inlinethumb18.webshots.com/21521/2305364400057637280S600x600Q85.jpg

http://inlinethumb32.webshots.com/42143/2135459110057637280S600x600Q85.jpg

ok...found the problem in car #2. Since every possible thing had been repalced and also checked I decided to start ruling things out. I pulled car # 1's POA replacement tube off and put it on car #2 and that was the problem. I had sent car 2's poa out to classic air in tampa to be rebuilt and obviously something wasnt right. Now I have cold air! The car is 100% original so i dont like the replacement tube on it but will deal woith it for now.
car #1- i pulled the evaporator out and there was dirt and leaves on inside. I ordered a new evap because it had green dye on it and i suspected my leak was coming from there.

ok...found the problem in car #2. Since every possible thing had been repalced and also checked I decided to start ruling things out. I pulled car # 1's POA replacement tube off and put it on car #2 and that was the problem. I had sent car 2's poa out to classic air in tampa to be rebuilt and obviously something wasnt right. Now I have cold air! The car is 100% original so i dont like the replacement tube on it but will deal woith it for now.
car #1- i pulled the evaporator out and there was dirt and leaves on inside. I ordered a new evap because it had green dye on it and i suspected my leak was coming from there.

Good detective work! I sure hope you had access to a recovery/recycle machine for all of that R12. Ouch..$$$

There's a test procedure for the POA over at www.autocaforum.com if you ever need it. It's in the tips and FAQ section. There's a a lot of info on POA systems in general and A-6 compressors too.

I'm surprised that the POA wasn't working right after it came back from Classic. They have a very good reputation. Anybody can make a mistake I guess. Are they going to help you out on fixing/replacing the POA?

Good Luck, Tom

we did the test procedures and it seemed to check out fine. i had a gut feeling it was it.They seem reall nice at Classic auto air. I have to calll them tomorrow and maybe send it back to get re worked. I may just keep the replacement tube on for now. Works great and i dont have to worry about it. My buddy has a shop and as the recovery tank for the r12 so dont have to let the ac shops steal it from me and sell it back to me. The ride home from the shop it was so cold i had to turn it on low. I do haave an issue with the middle vents. Its bowing about 5 degrees warmer than the side vents. Any reason for that?

we did the test procedures and it seemed to check out fine. i had a gut feeling it was it.They seem reall nice at Classic auto air. I have to calll them tomorrow and maybe send it back to get re worked. I may just keep the replacement tube on for now. Works great and i dont have to worry about it. My buddy has a shop and as the recovery tank for the r12 so dont have to let the ac shops steal it from me and sell it back to me. The ride home from the shop it was so cold i had to turn it on low. I do haave an issue with the middle vents. Its bowing about 5 degrees warmer than the side vents. Any reason for that?

It's nice to have friends.:D

No great idea on the vent temp difference. Leaks pulling in hot air from under the dash would be my guess.