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Really ready to give up, please look at syptoms!

92470 on Mon September 03, 2007 6:17 PM User is offline

Year: 1971
Make: Chevrolet
Model: C-10
Engine Size: 350
Refrigerant Type: R134a
Ambient Temp: 92
Pressure Low: 30
Pressure High: 260
Country of Origin: United States

Just road tested the A/C in my truck, and have mixed results. I posted about this vehicle previously, but if I can't figure it out for this last time, I'm giving up. Too much money and frustration and I'm ready to snap!

Truck has new evaporator core, drier, rebuilt POA calibrated for R134, rebuilt compressor, expansion valve, and was thoughly flushed and vacuumed. Original R12 capacity was 54 ounces. I put in 48 ounces. Low and high pressure seemed O.K. Vent temps were marginal at 55 degrees. Everything seemed to operate though, and while I would have liked it too be cooler, I called it good.

Took it out on a drive today, highway and in town. Temp was about 92 today. I didn't record vent temps, but it seemed cool, then not so much, then cool again. Pulled into a parking lot and looked under the hood. The lower evaporator tube going into the expansion valve was iced completely over. The expansion valve was frosted too on the bottom part. The POA was cold and sweating. There was also no moisture coming out of the evaporator core case. I put my finger up the tube, and it was dry. About 10 minuted later, water started dribbling out. This seemed strange.

Given what I have said about the lower evaporator core tube becoming iced, the sweaty, not icy POA, and late moisture to come from evaporator case, does all this sound normal to you folks?

I'm thinking either 3 things.

1. System overcharged

2. POA calibration incorrect and causing evaporator core to freeze.

3. Bad expansion valve.

Any advice or ideas are greatly appreciated! This is truly driving me nuts and I would love to have it fixed before winter at least!!!

Chick on Mon September 03, 2007 6:47 PM User is offlineView users profile

What about the oil bleed line from the POA ?? It could be clogged.. The location of the sensor for the expansion valve is also important..Has to be clamped tight to a clean surface and tapped with that black tape (prestolite we used to call it??) The POA seems to be working with the 30 low side...

Email: Chick


Freedoms just another word for nothing left to lose

Dougflas on Mon September 03, 2007 6:55 PM User is offline

Was this the one that had the POA calibrated to 20lbs? If so, did you recalibrate it to 26 lbs? What city and state are you in? (just curious). At 20lbs evap pressure, you will freeze up the evap. The result will be less air flow thru the ducts, no condensation dripping from the drain hole. As a result, loss of cooling. The whole idea of the POA is to provide a constant pressure in the evap. (A pressure that relates to a temp above freezing). You can test then tXV on the vehicle. Loosen the sensing bulb, put it in your hand. Pressures should change. Then put it in ice. Pressures should change. Clamp it on top to 3 o'clock position on the line tightly. Insulate it with the black cork tape. (called presolite tape years ago). Any other lines frosted? Frosted lines indicate restrictions. What is the low side with the engine AT 1200 TO 1500RPM AND BLOWER MOTOR LEAD DISCONNECTED? Then check it after your loss of cooling.

Edited: Mon September 03, 2007 at 7:01 PM by Dougflas

92470 on Mon September 03, 2007 7:02 PM User is offline


I wouldn't think the oil bleed line would be clogged (how do you check?) being the evaporator core is brand new and so was the POA. I jusst don't know what would have gotten in there? As far as the expansion valve, I one I bought a cheap one with a pig tail bullb on it vs. the long flat bulb. I was hesitant about the pig tail bulb because I can't see how it contacts near as well? It is very well insulated though with butyl tape as it should be.

I really hate to tear this thing back apart again. Should the lower evaporator core line running into the expansion valve be iced over like that? That's why I'm thinking maybe expansion valve. If I replace, I'm buying the better AC Delco one with the flat bulb. It would be made for R12, but I don't think that particular part matters if it's for R12 or 134.

Do you think the 48 ounces of 134 sounds correct with a R12 capacity of 54 ounces?

What would you do if you were me at this point. With a recalibrated POA, it's gotta do better than 55-60 degree vent temps.

Dougflas on Mon September 03, 2007 7:08 PM User is offline

the flow of regrigerant is from the drier to the tXV then into the evap. If there is afreeze up at the TXV, it's most likely bad. Give it a ramp with the handle of a may be stuck. The type of sensing bulb (round vs. flat ) makes no difference. Different manufactures use flat, rounds, spring shaped). Try the test I earlier described.

Chick on Mon September 03, 2007 7:13 PM User is offlineView users profile

As doug mentioned if it's freezing "before" the TXV, the drier and or txv may be bad..Feel the lines into and out of the drier, same temp??

Email: Chick


Freedoms just another word for nothing left to lose

92470 on Mon September 03, 2007 8:12 PM User is offline

I guess I will have to run some more tests. No other lines were frozen other than the lower evaporator core tube. This is in between the TXV and the evaporator,so I guess that rules out a bad drier?

I will try the ice and hand test for my TXV to rule it out. I have to think the POA is working correctly with low side pressure of 30-32 at 1500 rpm? No one at Classic Auto Air can give me a straight answer as to what they calibrate them to. One guy says 20, one says 26? I'll try your blower lead disconnect test and see what low side does.

Guess I'll pulll my gauges out and start testing. This is getting really old and expensive.

P.S. I'm in Kansas City, Missouri. Know any good A/C shops, or just anyone that knows what their doing I can trust for a second opinion?!

Dougflas on Mon September 03, 2007 8:46 PM User is offline

The reason I asked your location was because you mentioned Classic Air in Tampa. I'm not that far from Tampa and was going to suggest you drive by here for help. It looks as if your TXV is bad. Try the sensing bulb test.

JJM on Tue September 04, 2007 7:52 AM User is offline

Are you using an internally or externally equalized TXV? My memory is going, but if I recall POA systems need an externally equalized TXV - one that has two sensors, the capillary bulb (temperature) and connection to the POA (pressure).

Either way, the TXV is probably your problem. I would go with the correct original GM TXV on this vehicle. The POA is probably doing it's job masking the bad TXV.


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92470 on Tue September 04, 2007 1:11 PM User is offline

I am going to try the TXV test procedure and see if I get a fluctuation in manifold readings. With the lower evaporator line freezing up, that does make me think it is a bad TXV.

For my information, when I put the sensing bulb in my hand, and then into ice water, what am I supposed to look for exactly? A fluctuation in my low side readings? And if it's bad, what will it do then?

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