Originally Posted by youracauthority.com

Pilot Operated Absolute (POA) Valve

Like the suction valve, the POA valve is a suction throttling device that is located at the outlet of the A/C evaporator and is used to control the amount of compressor suction on the evaporator.

The POA valve was used on some General Motors and Ford air conditioning systems through the 1970's. On these A/C systems, the compressor would run constantly whenever the A/C system was on. Under certain operating conditions, less compressor suction was required on the evaporator. The POA valve would then close off the flow of refrigerant, effectively reducing the amount of compressor suction.

Originally Posted by youracauthority.com

Cycling Clutch Orifice Tube - CCOT A/C System


General Motors introduced the cycling clutch orifice tube A/C system in the 1977 model year. The unique advantage to having a cycling clutch with a fixed orifice tube was that now, the only moving part on the A/C system would the A/C compressor. The fixed orifice tube, which provides a one size, fixed opening for the flow of refrigerant into the expansion valve had replaced the typical expansion valve or TXV valve that opened and closed to control the refrigerant flow into the evaporator.

The fixed orifice tube means that there is always a flow of refrigerant into the evaporator. In order to control the evaporator pressure and maintain the coldest possible temperature in the evaporator without freezing the condensation, the system was designed to cycle the compressor on and off.

The cycling clutch system meant that the typical normal pressure gauge readings of a properly operating system would have a wider range. Of course, the low side pressures would be at their lowest just before the compressor cycles off while the high side pressures would be at their highest. As soon as the compressor clutch disengages, the high pressures start to drop while the low pressures increase. That happens because the fixed orifice tube is always allowing refrigerant to flow through it, regardless of whether the compressor is on or off. As soon as low pressures began to rise causing a higher temperature in the evaporator, the compressor would cycle back on to pull the pressures and temperature down on the low, once again increasing the pressures on the high side. The cycle continues in a controlled manner that maintains mean or average pressures in the evaporator so that the A/C system can provide maximum cooling performance with the minimum number of moving components.

Understand that the CCOT or fixed orifice tube system is still slightly different than typical cycling clutch systems. In other system designs, expansion valves are still used to control the flow of refrigerant into the evaporator. Those typical expansion valves open and close to monitor refrigerant flow while the compressor cycles on and off to maintain proper evaporator pressures. The orifice tube system utilizes the fixed opening in the orifice tube which maintains a constant flow of refrigerant.

Originally Posted by highperf4x4 (Post 3400614)

That's the thing with a POA system, the compressor doesn't cycle. It just stays on. I haven't been able to check the high side pressure yet but the low side was reading about 25psi

Originally Posted by 70 Suburban (Post 3400739)

the compressor will cycle if there is to little freon or if the pressure on the high side is to high it will shut the compressor off. pressure will drop then it will come back onl. It looks like cycle.

Originally Posted by joe231 (Post 3400788)

25 on the low side is pretty low, it needs to be at least 35-40...
BTW, what is POA?
oh wait....are you running R-12 or R-134? that makes a difference in pressures.
I have seen the compressor go bad and it would still run but it would not build any pressure on the high side.

Originally Posted by JohnC (Post 3400790)

That's a Hyperism Joe. Guess he need's to have a quick guide for us! :lol:

Man I wish I knew more about A/C. Is it still the old R12 system, or have you converted to 134A?

Originally Posted by 70 Suburban (Post 3400851)

Poa should be about 28-30 max.. But you can update it to ccot

Originally Posted by 70 Suburban (Post 3400854)

If you are running 134 did you adjust the poa?

Originally Posted by joe231 (Post 3400892)

oh, found some info





so it sounds to me like your POA valve might be malfunctioning?

Originally Posted by mrein3 (Post 3401067)

IF everything else is working right, and IF you are still running R12, you need to add some. You should be in the 28-30 range.

Originally Posted by TheSebring (Post 3401851)

Trying breaking off the line to the condenser and see how long it sprays everywhere. If it sprays for over a minute, you HAD plenty.:uhmk:

Originally Posted by TheSebring (Post 3401851)

Trying breaking off the line to the condenser and see how long it sprays everywhere. If it sprays for over a minute, you HAD plenty.:uhmk:

Originally Posted by highperf4x4 (Post 3402724)

I wish you knew more too! :lol:

Originally Posted by highperf4x4 (Post 3403291)

I will just as soon as I figure it out. New compressor just locked up so you may want to learn from someone else.....................

Originally Posted by TheSebring (Post 3403528)

I'll tell you what, it may be an unorthodox way of trouble shooting, but I figured out that it had plenty of freeon. So it works.

Originally Posted by TheSebring (Post 3405634)

Priceless my butt.

Price of 4 barrel intake:200

Price of 4 barrel Edelbrock carb:300

Price of a new spare because the old one was used to try and tighten up new lug studs(and the old one was the FACTORY):100