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I am trying to charge a 68 with a factory stock R12 system. During the mechanical restoration I did, the entire AC system was disassembled. Has a new, rebuilt compressor and a new receiver. All lines and components were flushed. System holds vacuum.

When I try to charge it, I can only get 7 ounces to go in. The cylinder is not cold, it's in a bath of hot water. The pressure in both low and high side is 85 PSI at 80 degrees ambient with engine not running. Pressures do not change with engine running and compressor clutch engaged. I confirmed that both schraders are being opened by the hose fittings. I even tried to charge directly from the cylinder to the low and then the high side, nothing, no flow.

It acts like there is only 10% of the system's volume available to charge. I can't believe there would be a blockage, in fact, there would have to be two to isolate the rest of the system. How can that be possible? I don't see how I could have assembled the system incorrectly. Everything pretty much falls into place.

I am totally flabbergasted and puzzled on this! Please help!

Larry
 

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85 is high for the low side...and the system should just balance when the compressor is off...when the compressor is running high side should be more than 85...

If your using a prof set of gauges are you using them correctly... You are closing the high side valve when you are filling by the low side correct.. Otherwise if both valves are open you will balance both high and low side and produce positive pressure into the can... And if it gets high enough the can could burst...
 

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Discussion Starter #4
New set of ProSet gauges.

The pressures are with the engine off or on. Both gauges are balanced at 85 PSI which is about right for the static pressure with 80 degree ambient temp.

7 oz is all I can get in with the engine off or on with both valves open with engine off and only low side open when running.
 

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The system should only be balanced with ac off... Once running the high side comes up... If you open up both valves when running you balance both sides and most likely create positive pressure..

Your compressor may be turning but is the clutch engaging correct.. If it's low you might need to energize it with a jumper..to get the clutch to engage
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Shut your high side off or disconnect it completely.. Start the car.. Energize the compressor so the clutch engages open the bottle then the low pressure side..
 

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Well I re read your post.. You are engaging the clutch... The only thing left would be something blocking the system....could you have left a plug in?? Did u change the orifice tube??
 

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Well I re read your post.. You are engaging the clutch... The only thing left would be something blocking the system....could you have left a plug in?? Did u change the orifice tube??
Speedjester and Everett,

I thought about that. I'm not sure if it could be possible unless it was a plug down inside a fitting where I didn't see it.

I hope I wouldn't be so stupid to do that. But, I can't think of anything else that would cause it.

I did crack a receiver fitting, it had pressure there. I guess I need to tear into it again.

BTW, it's the old sight glass system, with a POA and expansion valve. I can't remember the name of this type of system! But, they don't have orifice tubes.
 

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Did not know they didn't have orifice tubes... To be honest I'm not to familiar with the older systems.... Figure there basically the same....

Before you go tearing it all down... Maybe you could pull the hose manifold... Block the low side of the maifold..start pulling vacuum and see if you can feel the vacuum building on the high side.. If you can feel vacuum building then the system is clear .... And would look at the compressor





Speedjester and Everett,

I thought about that. I'm not sure if it could be possible unless it was a plug down inside a fitting where I didn't see it.

I hope I wouldn't be so stupid to do that. But, I can't think of anything else that would cause it.

I did crack a receiver fitting, it had pressure there. I guess I need to tear into it again.

BTW, it's the old sight glass system, with a POA and expansion valve. I can't remember the name of this type of system! But, they don't have orifice tubes.
 

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Speedjester and Everett,
BTW, it's the old sight glass system, with a POA and expansion valve. I can't remember the name of this type of system! But, they don't have orifice tubes.
Since you know that I assume you also know how to charge this system. With the little experience I ever got on these old A/C systems I'll guess you are jumping the low pressure cutoff switch to engage compressor. I always suck the system down, put in one can (thru the low side) with high side closed. then jump sw start car and install the remaining. You're looking for pressures about 30 low side and 100 over Ambient on high side. R12 Freon is 70 PSI at 70 degrees so you 85 PSI sounds about right for a static system.

Jeff
 

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Discussion Starter #12
UPDATE:

I've been disassembling the system. On the POA valve, should I be able to blow through it? I can detect an extremely small flow coming out of the compressor end.
 

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Yeah, I have that test procedure too. I might be testing it soon if I don't come up with anything else!
 

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UPDATE 2:

I didn't want to do this, but with the POA valve removed, I applied shop air to the outlet of the evaporator. Air flowed easily through the system out through the compressor manifold's pressure port. My shop air is going through a desiccant dryer system so I feel confident it didn't overload the system with moisture.

Other than the POA not being able to flow, the rest of the system must be OK. Now I just need to determine if the compressor is OK.
 

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I would have started by just putting a low side gauge on and adding freon through the low side and see what the pressure does - that way you rule out any bleed off from high to low side in the gauge set. If doing this shows lower pressure on the low side the problem is in your gauge set somewhere or the way you have it hooked up / valves open / closed etc. You wouldn't want to fill it like this but it would help you trouble shoot anyway.
 

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You said you "flushed the system". Any chance you added too much oil to the system after the flush? You may want to dump the compressor and receiver/dryer, heck maybe all of it, and start with base oil amount for a dry system. It sounds like everything is cycling, and if the vacuum is pulling down good and nothing is freezing up, too much oil may be it.
 

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Yes, there will be minimal flow through the POA valve until it opens.
The purpose of the POA is to keep the evap at 30 PSI for 32°F out. Evap pressure can be measured at its service port.
The present system is not an comp cycling system having an orifice and low pressure cut out switch, comp runs all the time.
You could have a stuck expansion valve. However, you did not mention the comp suction side going into a vacuum so I assume all is good providing a good vacuum was performed. Too much compressibles, other gases, and it won't take a charge.

Of course, having a nitrogen bottle to pressurize the system to 150 PSI and check for leaks with Snoop helps, plus adding in some freon to absorb moisture, followed by another vacuum charge, you've just done a triple vac, ensures a dry system. A vacuum analyzer reading down to 500 microns ensures no leaks in the sytem.

With a good A/c system, the suction hose usually is frosted up to about 3-4 inches of the compressor inlet.
 

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69-er wrote:
"When I try to charge it, I can only get 7 ounces to go in. The cylinder is not cold, it's in a bath of hot water. The pressure in both low and high side is 85 PSI at 80 degrees ambient with engine not running. Pressures do not change with engine running and compressor clutch engaged. I confirmed that both schraders are being opened by the hose fittings. I even tried to charge directly from the cylinder to the low and then the high side, nothing, no flow." ------

69-er , You stated that the pressures did not change when the ac clutch engaged. Just because the clutch engaged does not mean the compressor is pumping. I have put many rebuilt compressors on that were defective. If it was pumping you would be able to feed the r-12 in the low side of the system. If you had a blockage on high side the pressure would sky rocket on high side. I would make sure that the compressor is pumping.

Just my 2 cents.
MasterTech
Dan.
 

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69-er wrote:
"When I try to charge it, I can only get 7 ounces to go in. The cylinder is not cold, it's in a bath of hot water. The pressure in both low and high side is 85 PSI at 80 degrees ambient with engine not running. Pressures do not change with engine running and compressor clutch engaged. I confirmed that both schraders are being opened by the hose fittings. I even tried to charge directly from the cylinder to the low and then the high side, nothing, no flow." ------

69-er , You stated that the pressures did not change when the ac clutch engaged. Just because the clutch engaged does not mean the compressor is pumping. I have put many rebuilt compressors on that were defective. If it was pumping you would be able to feed the r-12 in the low side of the system. If you had a blockage on high side the pressure would sky rocket on high side. I would make sure that the compressor is pumping.

Just my 2 cents.
MasterTech
Dan.
X2, This is probably an R6 cly compressor and it sounds like its not pumping or the end plate valves are stuck closed on the suction side.
 
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