Engine Size: 350
Refrigerant Type: 134
Ambient Temp: 83
Pressure Low: 24-42
Pressure High: 170-180
Country of Origin: United States
I have a 69 Camaro, factory air with the following changes. Old Air POA update, larger more efficient condenser and a Sanden 508 compressor using R134 Freon. The gauge readings (with an ambient temperature of 83 degrees and unknown high humidity) were 24-42/170-180 with 48 oz.(4 12oz. cans) of freon and the engine running at 1100 RPM with a stationary cooling fan in front of the condenser. The problem is that before the low side pressure switch (on the POA update) turns off the compressor (due to low pressure...24 lbs.) the A/C cools very well but, as the low side pressure rises, so does the cabin temperature. After adding 36oz. (3 cans) I thought it was acting this way due to low freon so I added the other 12 oz. without much change except for a slight rise in the high side. I'm trying to figure out why this is happening and if I can get the low side to run at a more constant range so the pressure switch won't cut of the compressor as frequently. The pressure switch is adjustable but I fear going too low, freezing up the evaporator, which would starve the compressor of oil. Does anyone know what my problem might be or how I could find out? Thanks
I can tell you how to fix it. Reinstall the POA valve and your compressor will not cycle at all and you won't freeze the evaporator, either.
I'll echo what topflite said. Make that "POA update" go away! Reinstall the poa valve, and let the system operate as designed. You have a cool car--you should have a "cool a/c" also.
I meant powerflite. Gues I've go golf on the mind.
I was beginning to come to the same conclusion...guess I listened to the wrong friends. Everyone I asked at the time told me they were great. Funny thing also...Old Air (makes the POA update) won't answer ANY of my emails. Maybe they know what you guys already know. Thanks
I don't know why they call them POA updates... they're actually POA downdates.
I too would reinstall the POA valve, and adjust it for R-134a. But one thing you can quickly do to slightly increase cooling performance is to reduce the cut out pressure down to 19-21 PSI... just as you would do with any CPS on an R-134a retro.
After talking to a local automotive refrigeration engineer that had experience with these POA updates (which he liked better than POAs) he suggested adjusting the switch to 20 psi to move the "window" a little closer to a tolerable level. He also mentioned that 20 psi difference from where the switch closes and opens is pretty standard. I just finished doing that and it appeared to solve the problem but I'm about to road test it to see how it does. If it is acceptable, I'll let you all know. Thanks
If this local "automotive refrigeration engineer" likes POA updates better than a real POA valve than he can't be much of an engineer. Anyone with a BASIC knowledge of MVAC or HVACR knows a continuously running compressor will cool better than one clacking on and off.
Folks pay a lot extra for the Carrier Infinity central A/C system because it has a dual speed compressor, that runs at low speed when cooling load is reduced, rather than clacking on and off.
In any event, why ask us then if you have this resource?
Just found him...he mentioned the fact that it was hard to find a properly working POA. Even a brand new one that has been sitting on a shelf for ? years. Sorry I offended you by stating what was happening. I'm just trying to find out how to get this working right even though there is a debatable device involved that is like asking what brand oil is best. Everyone has an opinion about everything and I'm just trying to sift through this and fix it myself. I feel that I'm close and since this local source is in business, I don't want to impose on him for any more free advise. I thought this was the right place to find the information I need.
Another thing I would like to find out is if measuring the temperature difference between the inlet and outlet of the evaporator is an indicator of freon charge? I was told that if the inlet was colder than the outlet, it was undercharged. Thanks
GM had at one time used the procedure of measuring the temp of the evap in and out lines. Then they said when the lines were equal temp, to add "X" amount of freon. I don't remember what the "X" amount was. This was in lieu of measuring in an exact charge. It got you in the ball park. POA systems used a receiver drier that stored some refrigerant. Charge was not that critical. There is no better system for a vehicle than a properly operating POA system. Fixed orfice systems work well at certain conditions but on vehicles, the operation conditions are subject to change continuously. That is why they are not charged using superheat and subcool parameters.
If you truly are trying to find out how to get your system working right, you'll install the POA valve. This is not a subjective discussion of what brand of oil is best, this is simply a case of physics and common sense. And it is not opinion either, it is fact. Does your compressor provide any cooling when it's off? Of course not. So why would it cool better going on and off, than running continuously? Would your vehicle accelerate faster if the engine turned on and off? Would you see better at night if your lights turn on and off? Why is this so difficult to understand???
POA or STV valves are usually removed because many simply don't know how they're supposed to work, and want to "simplify" the system. It's not an update at all. Air conditioning was a very expensive option back then, and manufacturers has to make damn sure the system delivered for all the money. Plus everything tended to be over-engineered in that era. Why wouldn't they have designed a cycling system instead, and do away with the cost of the POA??? But with ever increasing emissions and fuel economy standards in the 1970s, and air conditioning becoming standard equipment on more and more vehicles, manufacturers needed to cut costs. In 1977, GM was the first to start going cheap with CCOT - compressors clacking on and off - and the R4 compressor. It all went downhill after that.
But then continuously running compressors made a comeback, with the V5 compressor later in the 1980s. Compressors clacking on and off was affecting drivability on those smaller 4 and 6 cylinder engines; something that wasn't a big deal on the earlier bigger blocks.
This IS the right place to find the information you need. That is why we don't advocate ripping out POA valves like other sites, we advocating repairing the system properly to obtain the best results.
Ahhh, but what the heck does an old wrench turner like me know... you've got a local automotive refrigerant engineer, why don't you ask him about inlet and outlet temperatures and charge levels and post back? I'm willing to learn.
Edited: Tue July 17, 2007 at 12:51 PM by JJM
I get your point and I may well end up reinstalling the POA. I've owned this car since 1982 and for years now I've heard nothing but praise for this device. I finally bought one when I decided to upgrade my system and think I need to try everything before giving up. I don't like the cycling clutch system at all right now but I have to find out why so many people bought/like these since I'm so far into this. I can tell you know a great deal about automotive refrigeration and appreciate you taking the time to share your wisdom. In the end, I may very well be your ally. Thanks, Joe
I did end up adding some more freon and the readings look better. 20-42/215-225 @ 90 degrees ambient...39-55 center vent
I don't have a 69 factory manual, but my 67 manual calls for 41-43 F vent temps at 90 ambient. And by the way, what are your temps when the system has cycled off?
Hi jweb47. Take the time to do a search on this site by putting in "POA". This link http://www.autoacforum.com/messageview.cfm?catid=20&threadid=7567 is just one of many references to the long running POA story, and how to tweak it for optimum performance with r-134. Read, and learn, like we all have, on this subject, because so much work (and posts) have been done with this issue. You'll find it most readable and enlightening, and will become your own kind of "expert" on the subject, and you will then be able to judge for yourself what is right, when others start giving you advice that is bogus. These folks here are the real deal!
I did that yesterday and have just about decided to go back to the POA. I'm going to set up a test rig to see if mine is still good. Part of my decision is due to the maker of the POA UDs ignoring my requests for help for weeks now. I don't care how busy they are...they should be able to respond by now. As far as I'm concerned, I'm tired of begging them and feel they don't deserve my business.
If my valve is dead, do any of you know of any sources for these that are reasonable?
Also, thanks Joe for taking the time to help me.
There of millions of POAs out there. Go to your local junk yard and grab several . Get the best looking ones you can find. Preferably with sealed systems. I bought 5 for $5.00 each. Three tested good. Be aware there are at least 3 different port orientations on GM POA valves. Get the one that matches yours. Stay away from those "over restored" units you see on that auction site. Good Luck
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