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POA sw and trinary fighting one another, help please

7502yuma on Sat April 05, 2014 1:52 PM User is offline

Year: 1969
Make: Chevrolet
Model: Camaro
Engine Size: 350
Refrigerant Type: R134A
Ambient Temp: 70
Pressure Low: 30-50
Pressure High: 200-400
Country of Origin: United States

Hello, my project has evolved from last post. I have since moved on from my previous issue.
The system consists of a R4 compressor and a 1993 serpentine setup from a Buick Roadmaster. I have replaced the POA with a POA delete. There is a new condenser (parallel flow) from Vintage Air and their drier and trinary switch.
The best description that I can give is that the low pressure switch on the POA delete and the high pressure switch on the trinary switch seem to be fighting one another. If I leave both switches connected everything starts out working fine. Then, once the system builds pressure the pressure starts going high and shuts off at about 400 PSI. The trinary then remains open until the pressure reaches about 300 PSI the compressor engages which drops the POA switch pressure too low and kicks out the compressor. Once this starts it's a non stop event. I have tried going with a lower charge but then it kicks out the compressor because the POA pressure is too low which results in the same scenario of constant cycling. There seems to be no happy medium for the charge unless I totally bypass the POA pressure switch altogether. My concern then is the evaporator freezing. I'm sure someone has encounter this before right? If so please share, if not ideas are very welcome.
Thanks in advance,

Jag987 on Sat April 05, 2014 4:00 PM User is offline

I have never used a POA delete kit. I have never worked on a system with a POA valve. The closest I have come to working on one was sending it away because the system was open for over 10 years when I first saw it and the customer did not have a budget big enough to even get started on repairs. I have only been doing a/c work for about 11 years now so what I say here may not be correct and I hope someone would correct me if it is incorrect. Why not disconnect the low pressure switch? With the trinary switch being both a high and low pressure cut out switch, is a separate low pressure switch necessary on this application? Yes, I do realize the high and low switch are usually on different sides of the system so removing the low pressure switch will still allow the compressor to run with the low side being very low. Maybe I just answered my own question and it would not be a good idea to remove the low pressure switch.

I am here to learn, and am very interested it what others have to say on this.

I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

7502yuma on Sat April 05, 2014 4:40 PM User is offline

First, thanks for your reply. I considered that as well but the low side pressure went below 30 with the POA delete switch bypassed . I'm concerned that the evaporator will freeze. My understanding is that is why the POA was in the system to begin with.

Dougflas on Sat April 05, 2014 6:55 PM User is offline

Did you attempt to test the POA and TXV valves? POA and TVX systems were the best you could have in my opinion. Some POA's could be adjusted to function with R134a. So now you are attempting to redesign a system. Did you test the TVX? Is the temp bulb properly positioned and insulated? You will need to furnish more info. What is the temp if the input and output lines of the condenser? Is the airflow across the condenser actually going thru the condenser? Did you try to mist the condenser with a water hose? Is the evaporator clean?

7502yuma on Sat April 05, 2014 7:37 PM User is offline

Yes, I did try the POA it leaked so I considered my best option was to go the POA delete route. In hindsight not necessarily true. Perhaps getting the original reconditioned would have been the better path. I did research and didn't find out the downside until I committed. Yes, I did put a spray of water on the condenser, I also tried another large fan in front of the radiator. They both brought down the pressure but I'm not sure what the purpose is. Wouldn't an ir thermometer on the discharge line of the condenser be a better indicator of heat removal?

Dougflas on Sun April 06, 2014 12:42 AM User is offline

By spraying your condenser with water, it brought your pressures down. So that tells us that your existing condenser is not doing it's job. Look for an airflow across the condenser problem. Also, does your POA eliminator kit still use a TVX or does it make your system a fixed orfice system?

mk378 on Sun April 06, 2014 10:09 AM User is offline

In normal operation, you should never hit the HPCO limit. So something is fundamentally wrong, like no air on the condenser or a blockage.

Do you get cold air with the low side switch bypassed? It should get cold, but then like you said, it may eventually freeze. A better control scheme with a TXV system is to sense the evaporator temperature, if it is practical to install such a sensor on the car.

Make sure the condenser is installed properly, in at the top and out at the bottom. Most parallel flow units have the manifolds set up so the first refrigerant pass is through a larger number of tubes. It should be mounted so this group is at the top.

Edited: Sun April 06, 2014 at 10:13 AM by mk378

bohica2xo on Sat April 12, 2014 11:34 PM User is offline

And there it is!

Another electric fan success story. Cycling on the HPCO. Period. If you are opening the HPCO repeatedly you have a condensor that is not effective.

I also tried another large fan in front of the radiator. They both brought down the pressure but I'm not sure what the purpose is.

Well, obviously even a moderate increase in airflow brought the high side down. As a diagnostic tool it is telling you that your electric fan is not getting the job done.

"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

7502yuma on Sun May 18, 2014 11:40 PM User is offline

So to follow up the car is finished. Believe it or not it was not the electric fan. I had the original POA reconditioned by Classic Auto Air in Florida. BTW they did a great job. Installed and charged and the system works flawlessly. Thanks to all who helped with this issue!

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