I decided to stay with the r12 in my reinstall mainly because i had some r12 laying around, i charged the system and it was working great then the next day i had nothing but the pressure's where were they should be i suspect a blocked or stuck POA valve.The compressor is trying to pump but it seems it has opposition in the line. The problem is i don't have enough r12 left to evacuate and recharge the system after repairing or replacing the POA. Any ideas? Thanks

I decided to stay with the r12 in my reinstall mainly because i had some r12 laying around, i charged the system and it was working great then the next day i had nothing but the pressure's where were they should be i suspect a blocked or stuck POA valve.The compressor is trying to pump but it seems it has opposition in the line. The problem is i don't have enough r12 left to evacuate and recharge the system after repairing or replacing the POA. Any ideas? Thanks

What are the system pressures? (1000RPM, Max AC, High blower, doors open) This is important to know for diagnosis.
Did you pull a vacuum on the system and charge into the vacuum? Is the receiver/drier new? How long was the system out of service before it was charged?

Low side 30, High side 280. the low side start to rise as the ac runs.
Yes i pulled a vacuum, The drier is brand new. I don't know exactly how long the systems was out of use probably a couple of years. I also have a new condenser and i added R 12 compressor oil as the label indicated.
I hope this helps with the diagnosis. Thanks for the reply, Alan

OK. The high side pressure seems high (unless it's about 100 degrees outside). This "sounds" like an airflow problem over the condenser. What's the ambient temperature when you checked the pressure? What are you using for a cooling fan?

Try "misting" some water from a hose over the condenser. If the high side drops like a rock and you get some cooling, the problem is likely the fan clutch or debris between the condenser and radiator

I am getting no cooling at all,the evaporater pipes are room temp. also if i run the a/c for any length of time the compressor gets sluggish and the belt wants to slip, also the relief valve on the compressor vents freon in a burst until i shut it down.it seems that there is a obstruction preventing the freon from circulating through the system.

The evaporator has a small diameter line from the bottom to the POA. It’s used to remove oil from the evaporator. If the POA is stuck closed the evap will flood with liquid, where the oil return line connects to the POA there will be frosting. That small amount of flow should be enough to prevent the condition you describe. ” if i run the a/c for any length of time the compressor gets sluggish and the belt wants to slip, also the relief valve on the compressor vents freon in a burst until i shut it down.”

I suspect the problem is with the expansion valve. If it’s stuck closed you’ll experience what you describe. Could also be the screen in the expansion valve inlet, but it’s unlikely it will be totally plugged. If there is any flow at all there will be frosting at the blockage.

The evaporator has a small diameter line from the bottom to the POA. It’s used to remove oil from the evaporator. If the POA is stuck closed the evap will flood with liquid, where the oil return line connects to the POA there will be frosting. That small amount of flow should be enough to prevent the condition you describe. ” if i run the a/c for any length of time the compressor gets sluggish and the belt wants to slip, also the relief valve on the compressor vents freon in a burst until i shut it down.”

I suspect the problem is with the expansion valve. If it’s stuck closed you’ll experience what you describe. Could also be the screen in the expansion valve inlet, but it’s unlikely it will be totally plugged. If there is any flow at all there will be frosting at the blockage.

The Expansion Valve is new, Is it not out of the question that it was bad to start with? When i first filled the system the lines frosted up on the low side then melted off, the lines where cool not cold after that. another sympton i did'nt mention earlier that may be important. Could it be i was shipped the wrong expansion valve not for an R12 system? Thanks, Alan

Sometimes the expansion valve inlet screens will stop up fairly soon after getting an old system going.

What that often causes is high head pressure from an overcharged system by trying to get the suction pressure up to normal thru the screen's restriction.

I am getting no cooling at all,the evaporater pipes are room temp. also if i run the a/c for any length of time the compressor gets sluggish and the belt wants to slip, also the relief valve on the compressor vents freon in a burst until i shut it down.it seems that there is a obstruction preventing the freon from circulating through the system.

Try the water mist on the radiator! With little or no airflow over the radiator the high and low side pressures will climb until the relief valve opens, just like you describe.

Sometimes the expansion valve inlet screens will stop up fairly soon after getting an old system going.

What that often causes is high head pressure from an overcharged system by trying to get the suction pressure up to normal thru the screen's restriction.

True enough, but wouldn't the suction pressure be low? On this vehicle, the suction pressure climbs, along with the head pressure.

True enough, but wouldn't the suction pressure be low? On this vehicle, the suction pressure climbs, along with the head pressure.
I was thinking the 30# was after the rise, but you are correct (as usual) a restriction would cause low back pressure.

Got a name?

I was thinking the 30# was after the rise, but you are correct (as usual) a restriction would cause low back pressure.

Got a name?

Naw, not "as usual". I'm wrong a lot, just ask my ex-wives and my teenage kids.:D My name is Tom, I'm from about 35 miles west of Cleveland..

Sometimes the expansion valve inlet screens will stop up fairly soon after getting an old system going.

What that often causes is high head pressure from an overcharged system by trying to get the suction pressure up to normal thru the screen's restriction.

How do you clean out the system before replacing the expansion valve so it won't clog up again?
I thought that i might also change to an update poa while i have the system empty. Any thoughts

How do you clean out the system before replacing the expansion valve so it won't clog up again?
I thought that i might also change to an update poa while i have the system empty. Any thoughts

This would be done by flushing with a solvent. Most of the metal inside an AC system is bare aluminum, and you've seen how bare aluminum corrodes right. Imagine that dust and debris all through the system. That's where I was headed when I asked how long the system was out of service. I meant to ask if it had been open for quite a while, but I forgot to follow up. If it's really corroded, you have to replace parts.

If, by "update POA" you mean the kit that eliminates the POA and makes it a CCOT system, I'd think twice if I were you. They're not bad or harmful, and work ok. The system as designed, with the POA valve is far superior at pressure and temperature control.
The jury is still out on the issue of clutch wear on the A-6 compressor. The clutch wasn't made to cycle and there is some concern about clutch life. I haven't seen this problem but thought I'd toss it out there.

Here are my thoughts.

The low side pressure tap is on the evap side of the POA valve. If the POA is working correctly you won’t see less than 28 psi. evap pressure. If you could read the actual compressor suction pressure it is likely under a vacuum.

” Low side 30, High side 280. the low side start to rise as the ac runs.”
How high does the low side go?

You should be able to locate the blockage as there will be a noticeable temp drop across it. That is unless the blockage is stopping all flow. If the evap pressure increases that tells me there is some flow.

There may be blockage in the new condenser or the dryer. The fact that the relief valve opens indicated the blockage is before the dryer. The dryer is also a receiver it along with the condenser should be able hold the entire system charge without opening the relief, that is of course if you have adequate air flow across the condenser to condense the gas to a liquid.

Other than the aftermarket POA shown below I don’t know if a suitable replacement and I don’t know of a source for the pictured POA.

The screen at the inlet to the expansion valve is or should be removable for cleaning. To flush the system there are kits available for that purpose. Kits run about $300, the chemical is about $40 a gallon. It may be cheaper to have a mobile AC shop do the flushing.

[QUOTE=lsrx101;1364062]This would be done by flushing with a solvent. Most of the metal inside an AC system is bare aluminum, and you've seen how bare aluminum corrodes right. Imagine that dust and debris all through the system. That's where I was headed when I asked how long the system was out of service. I meant to ask if it had been open for quite a while, but I forgot to follow up. If it's really corroded, you have to replace parts.



The parts and hoses where covered with plastic bags cable tied. As for a flushing solvent, what would i use and how do i circulate it through the system then out. I really appreciate this help. Thanks

” Low side 30, High side 280. the low side start to rise as the ac runs.”
How high does the low side go? 45

there is no cooling anywhere in the line.
when adding r12 the site glass shows fluid movement,wouldn't that indicate that the dryer is working?

what would i need to flush the system kit wise? there are a very few choices for a/c repair shops in the area where the car is kept. Thanks

[QUOTE=lsrx101;1364062]
The parts and hoses where covered with plastic bags cable tied. As for a flushing solvent, what would i use and how do i circulate it through the system then out. I really appreciate this help. Thanks

Is it safe to assume that the system was never left open (You know, hoses off, compressor in the corner of the garage) for a long period? If so, Dura 131 flush slovent can be used along with lots of dry compressed air. (lacquer thinner also works very well) As Elree Colby mentioned, there are other flush options also depending on the amount of contamination . The system needs to be totally disassembled and each part flushed individually. You don't flush the POA, expansion valve, receiver\dryer, or the compressor.

Before you tear into the system, try misting water over the condenser and see if the pressures fall into line and it cools. Your problem could be as simple as a pooped out fan clutch. There are a few things that can cause these symptoms, but the water mist is free and takes 2 minutes. Keep it simple...

No cold spot on in the system is a good sign. The sight glass isn't a good indicator at the moment.

[QUOTE=lsrx101;1364109][QUOTE=snowtrav;1364075]


Before you tear into the system, try misting water over the condenser and see if the pressures fall into line and it cools. Your problem could be as simple as a pooped out fan clutch. There are a few things that can cause these symptoms, but the water mist is free and takes 2 minutes. Keep it simple...


Thanks for the info. I will try the misting water idea first,i would rather not take everything apart again if i don't have to. Alan

Update: I tried the misting water over the condenser as recommended there was no effect.the low side was low 15 so i added more gas and as i was doing that the high side started to rise 350 and the compressor started to labor. I am strting to thing there is a complete blockage in the system.

check the Xvalve inlet screen,


Sometimes the

expansion valve inlet screens will stop up fairly soon after getting an old system going.

What that often causes is high head pressure from an overcharged system by trying to get the suction pressure up to normal thru the screen's restriction.

I recovered the R12 and emptied the system and removed the hose from the expansion valve and it was loaded with chunks of something hard, obviously that was my problem as you guys indicated. I guess i am off the the parts store to get a flush kit as recommended by lsrx101. The only question is whether i should I go ahead and convert to R134a ? I can still get the r12 but its pricy and i don't know how long i can get it. Thanks to All

Bummer! Do you know what the material is? Aluminum oxide would form a coarse paste. Hard chunks could be compressor parts or desiccant from the dryer. I don't recall, did you replace the receiver/dryer?
Changing to R-134a will work, but the POA valve should be recalibrated for the system to work at it's best. It's not mandatory, but if the car is a dark color and/or has a dark interior, you may not be happy with the results. Since you are disassembling the system to flush it, you will be replacing all of the seals, so you might as well stay with R-12. The price is coming down due to the low demand and you will only spend the money once if the system is tight. Just some things to consider.


I went back and saw where you said the R/D was new. The desiccant bag could have ruptured, but it's more likely to happen on an old one. Can you post a picture of the debris that was in the screen?

Ok, i flushed the system and changed the expansion valve for 134a.i started to charge the system and the compressor side of the poa is cold and frosting as well as the small tube to the evap but the evaporator side of the poa is not cold. i only have 24 oz of 134a in the system, would this cause this. or is the poa stuck this time. How do you get it free. Thanks

(Waking up long dormant brain cells with POA information) I'm pretty sure this is normal. The valve is trying to keep the evaporator pressure at ~30 psi and the suction line is in a vacuum. Pressure differential=frost.
Keep charging and monitor the pressures. That system held about 3-3.5lbs of R-12 IIRC, so you're still way undercharged.

If the POA valve is stuck, there's no good way to free it up DIY.

Update: I finished charging with 134a and the pressures where a little high so i let it sit for a week while it settled down. after a week i started the car and turned on the a/c and it works great, the low side is about 27 and the temp out of the vent is 39 degrees. Thanks everyone

I have a 71 chevelle in my shop now to repair ac. Car came in with a nused compressor, a new drier, a new xvalve, original poa valve, a new aftermarket condenser and no freon.Charged system with r12 to see what I had- compressor on- low pressure 50 @750 rpm high pressure 350 @ 750 rpm. Unpluged blower raised rpm to 1500 low side 27-poa is working. Replaced flex fan with 6 blade gm and hd fan clutch. high side now 300 low side 50 on high blow. Noticed tubes on aftermarket condenser somewhat smaller than original, replaced condenser with new delco, high side 210 @ 750 rpm low side 50. Found cowl vent door missing- blower is pulling engine heat over evaporator with hood open. Closed hood blocked of outside air- bypassed heater core- low side 40 @ 750 high blow. Ice cold ac. Hope some of this info is helpful. ps the a6 compressor moves more freon than any other compressor. It does not like restrictions or high discharge temps. I believe that the condenser in this car was contributing to 50% of the problem????