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Old 08-21-2020, 01:40 AM
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Default POA VALVE OR CYCLING SYSTEM

Redoing the AC in our 69 FB. Considering changing the POA valve to the cycling type system. Still staying with r12. Anyone have any experience with the cycling style system verses the stock POA valve? Blow colder?
Looking at: 50-2552 - POA Update KitPOA Update Kit for GM Applications w/ R-12, to Convert to Cycling Clutch System. Thoughts?

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Old 08-24-2020, 09:42 PM
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I absolutely hated the POA replacement system with the pressure switch and went back to a POA valve. We fought and did everything we could think of but the system would cycle with vent temps getting down to 38° and then cycle off with temps going up to 46°. We could lessen the span but it would then cycle 42 to 44 degrees. Put the system back to stock and we had 38° all the time. This was with R12 and we just couldn't shorten up the cycle without raising the output temps. Inside the cabin I would just start thinking that things should be cooler and it would kick on and get cooler, then up and down over and over. Came across the Arizona desert with outside temps at 105° and we were always comfortable, although that was just on the edge of comfort with no room to spare. All we did was put the original POA valve back in and recharge the system so we ruled out something else being off.

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Old 08-24-2020, 11:40 PM
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We installed the poa update kit on our r12 system. The initial setting caused the ac to blow 39f then shut down rising to 50ish. Hot cold like the the prior person said. I adjusted the pressure switch 1/2 turn counter-clockwise and 45F most of the time. At one point it may have frozen up, Temps began to climb, so i shut it off a few minutes. Tomorrow I will try turning the valve 1/4 clockwise to see if i get closer..

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Old 08-24-2020, 11:50 PM
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my real question regarding poa valves and new style system is this. I weighed in 60 oz of r12 like the service manual indicates.this resulted in a clear sight glass and pressures of about 40L / 240 high with an outside temp of 96F. Would it be better to remove some freon to get closer to the 30psi target to eliminate the need to cycle the compressor to drop the temps to keep it from freezing up?

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Old 08-25-2020, 01:32 AM
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Not sure but would think low pressure would be the same between valves. What vehicle?

In general terms if low side is too high (30 vs 40) it is either too much Freon or an obstruction in the system. Easiest would be to drop the running pressure to right where you see your first bubbles. Things get complicated with different ambient temps and such, but I usually find the best results just after the bubbles clear off even if I'm not at the required weight.

Would be nice to hear from an A/C tech -- I'm home schooled and only one step above staying at a Holiday Inn the night before. It cost me a lot of money finding out that the shops in my area didn't know what they were doing, and I've had better luck on my own with trial and error.

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Old 08-25-2020, 01:33 AM
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My car is a 71 T/A and I eliminated the POA valve totally and used an accumulator instead. I live in South Fla. and no complaints from my car and 2nd Gens have the worst reputation for A/C. I made sure all the duct work is sealed best possible, accumulator and no moving parts except the compressor it self. Oh, forgot; I also changed the A6 to an R4. Charged with 134A.

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Old 08-25-2020, 03:16 AM
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The GM service manual for my 69 firebird sais to install 44 oz of r12 to clear the site glass up and then add 60 total oz. It specifically sais that while it will cool with the bubbles just cleared. It will perform overall better with 60 oz in. I realize you can still be 100% correct that in the real world it may be cooler at 44oz, but gm thought otherwise. Fully charged the low side is in the 40s, and the POA valve would bypass the extra 10psi. With the cycling set up, it shuts off the compressor at 40, creating a warm spot in the ac flow. That makes me think possible lowering the low side to be at 30 psi might help since it won't cycle off, keeping the air colder. More experimentation required.

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Old 09-11-2020, 03:15 AM
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Ok, poa update. The pressure switch on the POA eliminater turns the compressor off if the pressure goes below 20psi and back on at 43psi to prevent the evaporater from freezing . I had to fine tune the pressure switch, eventually turning it counterclockwise to about 7 o'clock. At idle my low side is 30psi, but at cruise it was dropping to 22 and shutting the compressor down. I adjusted until the system continues to turn at 75 mph. It cycles briefly to prevent freeze up. About 37f vent air is the best I can get, which beats the 60f air others with 134a are getting.

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Old 09-14-2020, 12:29 PM
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If you still have the original A6 compressor, the clutch was not designed to cycle off/on like on the newer systems. Good luck

Sent from my SM-T817V using Tapatalk

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Old 09-14-2020, 09:31 PM
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I have always raised the idle to 2000 RPM and filled Freon till the low side is at 30PSI. Never any issues. Solves your problem. Make sure you have enough air coming through your condenser while doing this. A6 compressors are sensitive to overly high high side.

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Old 09-14-2020, 10:38 PM
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I replaced the A6 with a S6. Same displacement as the A6, but only about 4 hp verses 17?

I like the idea to keep filling till the low side hits 28 to keep it from cycling. I wondered why that wasn't the orginal plan, seems like it may cool less at idle, but worth a try.

What centet air vents are most achieving with r12?

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Old 09-15-2020, 01:36 AM
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I was trying to say, what are most muscle cars achieving in output temps on thier Ac?

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Old 09-15-2020, 08:04 AM
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I get 46* at the center vent.

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Old 09-15-2020, 02:32 PM
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I need a refresher course here because it's been too long since I've messed with a POA replacement valve. From what I remember the lower the pressure on the low side the cooler the vent output, but there were consequences to setting the turnoff point too low. Doesn't it freeze up the evaporator if not allowed to cycle? How about the high side pressure - doesn't that climb as the low side falls? These are just questions and just trying to remember why the cycle switch wasn't normally set lower? Otherwise we would just set it where it never cycled the compressor off.

As far as the question about vent temps, when I had the replacement POA tube my vent temps would get down to 38° and then shut off until 46° and do the cycle over and over again. When I went back to R12 and original POA valve the vent temp stayed at a constant 40° when testing.

Unfortunately our numbers really don't mean much unless we list the ambient temperature and other conditions. Basically my results are only for the conditions of that particular day I worked on the car. Say the outside temp was 92° with low humidity and the car was in the shade. I also have some large fans blowing into the radiator and they work well enough that I usually don't hear the severe duty fan gear up. The guy down the street with his car hot soaking in the sun with no extra air flow won't have as good of results even if his system might actually be cooling better than mine.

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Old 09-15-2020, 03:34 PM
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Yes, you have it correct. My initial post, I was confused myself.

When you remove the POA valve and replace it with a POA bypass tube, it is fitted with an adjustable pressure switch that controls the cycle on/off of the compressor. This is on the low pressure side of the evaporator.

The evaporator condensate will freeze up if the low pressure to it drops below 30F. The pressure switch actually shuts off the compressor when the pressure drops below 30psi on the low side, and returns power to the compressor when the low side reaches at least 43psi. However, these set points are jointly adjustable on the pressure switch. (one adjustment sets both on and off cycle)

Initially after installing the POA eliminator my system would blow very cold (38F) at idle where my low pressure was 30psi. When I drove the car, the additional RPM's would cause the low side pressure to drop to around 20psi, and the compressor would shut off. Eventually with no running compressor, pressure would equalize in the system, and when it reached around 43psi it would turn the compressor back on. The result was 38F air initially at idle, then the temps going up to 65F plus with no running compressor, then the compressor re-engerized drops the air temp again, repeat. I would get 5 seconds of 38F and 30 seconds of hot air. Not good. (ambient temps 95F)

I began turning the pressure switch adjustment screw counterclockwise 1/8 turn at a time until the system would continue too run at cruise speed. I believe this was causing it to freeze it up as after a few miles airflow would drop and air temps would rise. I have made minor changes to try and find a sweet spot, and I can now get 47-55F air now most of the time, as I suspect the system is briefly dropping out occasionally. Still not great.

As all can see, the POA eliminator is a poor engineering replacement for a POA. The POA is a pressure regulator, not a pressure switch. It is set to allow the evaporator to constantly get 30PSI low side pressure and as compressor speeds change, then it bypasses (regulates) any extra. Since new POA valves aren't available, the 8 week wait for a $200 rebuild is an issue, hence the move to the eliminator valve. I propose it be renamed the "cold air eliminator regulator".

I have wondered if you added additional freon to maintain a low pressure of 30psi at cruise speed, the compressor should be able to run continuously without the evaporator freezing up. Likely at idle and low speed cruise the low pressure side would be higher and less efficient since the compressor is spinning slower, sucking less. I think while my POA valve is being rebuilt I will try adding more r12 and see if that results in an AC that doesn't freeze up and still blows colder air.

Many add the POA eliminator and have no complaints. On these systems I have checked, they are blowing 55-65F air from the vents. They sure aren't freezing up. The owners are just happy it cools some. With our convertible, 60F air isn't worth the trouble since the interior space is so hard to cool anyway. I'm looking for air in the mid 30's to create an effective AC. (like GM thought also)

If you have a POA or POA eliminator system and have cold air anywhere in the 30's, tell us how you did it, please. But please test the temp first as many who have claimed to have ice cold air had 55F temps.

If you got here, because, like me, you couldn't find any user info on POA eliminator systems, my recommendation and experience so far at this point is rebuild your POA valve. GM understood how to make continuous cold air, and so far, the other system functions, but doesn't PERFORM.

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Old 09-15-2020, 04:28 PM
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Exactly what I found. More power to the people that got the tube to work, but regardless of my adding or subtracting Freon, the system remained marginal. You did remind me that as the pressure switch was lowered the wait time after the unit clicked off was extended. I found myself choosing the best compromise between vent temps and off time. My ranges always looked like 38-46, 40-48, 42-50 or about an 8° spread. Only thing that changed was the off time decreased as the bottom temp went up, and set high enough the unit would stay on without cycling but the vent temp was stuck in the mid 50's.

I lived with it for a summer where we were comfortable to almost not comfortable. Went back to the original POA valve and changed nothing else and system worked good with none of the roller coaster temps.

For those that haven't seen the POA replacement unit, there is nothing to go wrong except the pressure switch since it is just a hollow tube you can look straight through.
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Old 09-16-2020, 07:27 PM
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Nice to hear some of you guys are using R12. Where can it still be purchased without mortgaging the house?

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Old 09-17-2020, 03:21 AM
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Price dropped pretty low a few years ago and has went back up. There was a point where everyone was converting to 134a and the demand really fell for the R12. I still have a fair stash from years ago and no need to purchase any, but I just looked through eBay and if I were going to buy it today I'd probably go with the dozen cans of R12 for $425 plus $25 shipping. That's $37.50 a can including shipping but before tax. Considering that many years ago a can was selling for $75 around my area, the current price isn't too bad. Have to watch a lot of the sellers because of their calling their product R12 and then in fine print acknowledging that it is a "R12 replacement gas".

A few years ago there was an eBay seller around your area that was advertising R12 from the Dupont factory in Mexico that was still in high gear producing it, and I suspect he was bringing it in and advertising it as being manufactured before the ban. It was good Freon and I just used the last of what I purchased years ago recharging the wagon's factory AC system. Anyway, you might check the local advertisements and see if he might still be advertising locally on Craigslist.

Pound is 16 ounces and these cans are 14 ounces, so usually just get into the 5th can for a fresh full charge. The bummer is that my partially used 5th can is always empty by the next project.

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