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expansion valve question

6769GM on Sun July 07, 2013 1:53 PM User is offline

Year: 1969
Make: Chevrolet
Model: Caprice
Engine Size: 350
Refrigerant Type: 134a
Country of Origin: United States

I have a 69 Caprice with the Comfortron system. i just installed the 134a after changing the accumulator and vacuuming out the system. Held vacuum for days. Once charged, it still was not cooling. Today I tapped on the expansion valve and it frosted up, the line to the evaporator did start to decrease in temp (but not much), and the line coming out of the evap never got cold. Could it be the expansion valve? Any chance the POA has an issue? The car only has 60K miles, but did sit up for about 24 years.....any help is appreciated!

mk378 on Sun July 07, 2013 3:59 PM User is offline

What are the pressures? How much R-134a did you use (it should be close to but not more than the specified amount of R-12)?

6769GM on Sun July 07, 2013 5:14 PM User is offline

it called for 60oz of R12. Right now it has about 44oz of R134...low side is about 40, but will need to recheck. I tried the AC again this afternoon and the expansion valve continues to frost up and the line to the evap will cool off slightly. The line out of the evap to the POA is still warm.

fonebone on Sun July 07, 2013 5:22 PM User is offline

Hi 6760GM; This does not sound too good. You only changed the receiver/drier(not called an accumulator on these early systems) and that's it????? Did you flush all mineral oil out? NOT compatible with r-134! Add the proper oil and the proper amount for this system? Much has been posted in the archives here for proper conversions to 134, and how to tweak the POA valve for best cooling. It's a lot of work to get anywhere close to r-12 cooling levels. Almost all here would have told you to stay with r-12!!

6769GM on Sun July 07, 2013 5:25 PM User is offline

the system was cleaned out and the new oil was added. Would a POA update kit be advisable?

mk378 on Sun July 07, 2013 5:38 PM User is offline

You need to get both pressures. If the high side is staying in a safe range you should add more refrigerant. Frost at the expansion valve but the whole evaporator not getting cold is typically what happens when undercharged. This will also happen if the TXV is not working properly but you need to be sure its a full charge to differentiate the two.

Also frost means the pressure at that spot has to be lower than 40, since the refrigerant would not get that cold otherwise. 134a can work good in a POA system if the condenser is up to the task.

Edited: Sun July 07, 2013 at 5:42 PM by mk378

6769GM on Sun July 07, 2013 5:41 PM User is offline

Thanks...what should the pressure be running for the high side? Based on the 80% rule that I have seen, the quantity of R134 should be about 48oz, correct?

mk378 on Sun July 07, 2013 5:43 PM User is offline

High side psi
Did you test your POA valve with air while it was taken out?

Edited: Sun July 07, 2013 at 5:47 PM by mk378

fonebone on Sun July 07, 2013 5:48 PM User is offline

Hi-Do not use a POA update kit! It's been covered here previously, and all agreed they are junk.Do some searching here and you should find threads talking on these subjects, especially how to tweak that POA valve for optimum performance. You sound undercharged, but again, because of the difference between r-12 and 134, you should read up on that. I know you probably don't want to pull the system apart again, but that is a way to get close to r-12 cooling. All here would recommend that when you had it apart to have replaced the less efficient tube and fin condenser with with an aluminum parallel flow unit(available here at this site). Did that on my 79 Caprice I still drive and it made a difference in a few degrees cooler temps. Also, for the summer, I use a non-thermal fan clutch that really pulls in the air, and drops the temps down fast from idle to highway.

Dougflas on Sun July 07, 2013 6:06 PM User is offline

POA systems need to change the operating point of the POA to 26psi. This usually equates to 1/4 turn counterclockwise of the adjusting nut inside the POA if it has an adjustment. Once you get the R134 level close (about 49 oz should get you in the ballpark), unplug the blower motor and read the low side at 1500 rpm. This should be close to 26psi (make sure your guages are zeroed before you start, If this is at 26psi, plug the blower motor back in. Let the system run and check the TXV for operation. I listed a proceedure in the proceedure section for a Chrysler ERP set up. The testing is the same.

If you open the system, why not replace the TXV with a R134 version? Your statement that you tapped the TXCV and it frosted up sort of points to the valve sticking closed.

One more thing...these systems do not require a percision charge as the cycling clutch systems do. The receiver/drier will hold some excess refrigerant. What you're looking for is a steday stream of refrigerant to feed the TXV. ant extra will be stored in the receiver. DO NOT RELY ON THJE SITE GLASS when using R134.

Edited: Mon July 08, 2013 at 6:43 PM by Dougflas

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