Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

[Tom L.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

If the TXV were stuck open you'd probably have a low head pressure, no significant restriction to build those kinds of head pressures. As I read this thread, one question comes to mind, you're sure you have "virgin" R-12, right? The pressures (Not temps though) you're listing suggest that perhaps you've got R-22 OR an unknown blend of some kind. If the refrigerant is correct I still vote overcharge. Good luck!

[Jim T.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

Mark, reference the new parts installed, did you replace the dryer? If you did not there is the possibility that the debris screen in the expansion valve could be affected by desiccant from your old dryer? I have experienced the bag of desiccant breaking open in the dryer and traveling through the condenser to the expansion valve filter screen and affecting the flow of refrigerant.

[Tom L.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

While I've seen all of these things happen, a restriction in any of the area's that Jim mentions would result in low suctuion pressure which seems not to be the case here. Suction pressure in this case is excessively high for any type of R-12 system.

[Mark P.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

Jim and Lynn---I had my original filter dryer rebuilt and installed when I changed expansion valve.

I am going to order some new R12 and a new filter dryer. I am unable to verify that the contents of my R-12 container is indeed R-12 as I purchased a partial container and used this container to charge the car. While I am waiting for the new R-12 to arrive, I do have some R-22 and I will charge a few ounces into my dial-a-charge and record the pressures. This I will remove some of the refrigerant that is in the car add a few ounces to the dial-a-charge and compare the pressures.

I will report back with the results-----Mark

[Tom L.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

You can check to see if the contents of your cylinder is R-12 by using the P-T chart I gave you the link to provided that there is still liquid refrigerant in it.

1. Using an accurate thermometer, record the temperature of the cylinder. It should be the same temperature of the room as long as it's not in the sun.

2. Then take a pressure reading of the cylinder (be sure your gauge is zero'd for accuracy) and record it.

3. Next, find the temperature in the left column that you recorded earlier, look at the correlating pressure in the R-12 column to the right. if it is R-12 the presssure you recorded from the cylinder should match exactly to the pressure found on the chart.

Of course the accuracy of your tools is essential. As long as it's close you'll know it's either R-12 or one of the many replacements that have been on the market for the last 20 years. Hope this helps. Good luck!!

[Mark P.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

Here are the results from my pressure temperature test of the refrigerant in my car versus a can of known R-12. I have removed the contents of the charge that was in my car, but did retain about a pound in a dial-a-charge for the test.

I moved both the dial-a-charge cylinder (refrigerant that was in car) and a known R-12 cylinder into my basement and let the temperatures stabilize for 24 hours. The pressure readings of the the known R-12 can 75 psig @ 73 degrees. The cylinder with the former contents of my car read 92 psig at 73 degrees.

It appears that I purchased a partial can of R-12 via the internet that was contaminated. The lesson here may be that when one does indeed purchase a partial container, you should immediately take a pressure reading on the cylinder to verify the proper pressure/temperature relationship.

Thank You for your suggestions and patience-----Mark

[Dick W.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

It appears that I purchased a partial can of R-12 via the internet that was contaminated. Mark

That is the very reason I will not pump down a system without testing to see what is in the system. Some of the junk you buy that is supposed to be refrigerant is scary. I have seen head pressures out the roof when someone that knew everything added R-22

[Larry M.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

That is the very reason I will not pump down a system without testing to see what is in the system. Some of the junk you buy that is supposed to be refrigerant is scary. I have seen head pressures out the roof when someone that knew everything added R-22

They can only go so high......that's what the compressor safety valve is for.

I think Mark was getting pretty close to losing all his refrigerant. I replied on "the other forum" that it appeared that he was using R22 or a mix or R12/R22.


Larry

[Mark P.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

I have elected to replace my oil and filter dryer before recharging the car.

While waiting for my new refrigerant oil and dryer to arrive I decided to bench test my expansion valve to verify that it will open and close. I put about 5 lbs of air pressure on the inlet of the valve and as expected at 85 degrees F air readily passes through the valve body. (Please note that the external equalizer is not connected and exposed to the atmosphere).


I then placed the thermal bulb in ice water at approximately 35 degrees and air still flowed through the valve body. I then prepared a salted ice bath and temperature dropped to 27 degrees with the bulb immersed in the bath----air still continues to flow through the valve body.


I then called Old Air Products from whom I had purchased the valve and spoke to a tech asking him for the proper method to verify that the valve is functioning properly. He said I need to refer to the GM specification. I explained to him my tests with the ice bath I conducted and he said "there is no salt water on the suction line so there is no comparison to be drawn by immersing the bulb in 27 degree salt water and expecting the valve to close". I thanked him for his time.


I attempted one last test by placing the new expansion valve's bulb in the freezer----I still can blow air through the valve body.


I do still have the expansion valve that came with the car and was working when I removed. Ironically it seems to test out exactly like the new valve I am trying to install.


My 67 Chassis Manual does not have any detailed data on the expansion valve. I am now wondering if it is even possible for the valve to throttle or close without the external equalizer being connected and reading the pressure of the POA.

Does anyone have a procedure for bench testing the expansion valve?

Thanks---Mark

[Larry M.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

Mark:

Excellent feedback on this problem. I agree with Dave regarding the external equalization line.......however, I am not certain that the expansion valve can ever close off completely. The compressor always needs some amount of refrigerant flow through it to keep cool and to keep from overheating. So I think the expansion valve will always pass some flow.

The reply from Old Air Products was unsatisfactory......they should have been more helpful to your problem.

At this stage of the game, I might be inclined to re-install the old expansion valve unless I could definitely tell that the new reproduction valve is working correctly. You KNOW that the old one worked.

You might also call Classic Auto Air in Florida and explain your problem. Don't know if they sell the same expansion valve, but they might be more helpful regarding how to test this valve. They state that they rebuild/restore original expansion valves, so they must have a test procedure.

Larry

[Mark P.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

Dave

I will rig a pressure test fixture to apply 25-40 psig to the equalization port.

Larry

It makes sense that the valve would never entirely close as you have stated. I plan to test both the new valve and the older working valve with the test that Dave recommended. I am going to see if I can borrow a mass flow meter and measure the flow volume when various temps are applied to the thermal bulb.

I will also give Classic Auto Air a call and see if they can recommend a test procedure.

Thanks---Mark

[Tom L.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

Mark, the operatopn of a TXV is reasonably simple. The goal of the valve is to be sure that NO liquid refrigerant passes beyond the evaporator. If it does, bad things happen to the compressor. All externally equalized TXV's operate on the same principle, the outlet pressure added to the internal spring pressure must equal the pressure in the Bulb, or diaphram. The valve will NOT close unless the bulb is discharged, it's the only thing keeping it open. Also, even if it were adjusted completely closed, not easy on these valves, it would only be closed to 50% of it's rated capacity (At least as a rule in commercial refrigeration)

Your test will likely be inaccurate unless the system is under operating conditions. If ther valve is new, undamaged and not contaminated I'd suspect it's fine.

[James G.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

Hello Mark,
Glad to hear you are still having fun with your 67 Black Coupe I found for you back in 2005. At least it ''sounds'' like fun. You have a great ''thread'' here on this topic, and we are all very curious about the outcome. All I can add is in the good old days (1967-1990) I used to get 34 degrees out of the center duct. My wife used to complain that ''You can hang meat in here !''

[Mark P.]

[Larry M.]

Re: Why was 3 lbs of R-12 Not Sufficient to Charge my AC?

Mark:

Excellent info and testing. Never would of thought of the "balloon test".....not in a hundred years. I might of used a gas rotometer though.

Keep us informed of your progress as work progresses.

Larry