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Help converting my 72 K20 AC to R134

Buds 72 K20 on Tue June 11, 2013 2:13 PM User is offline

Year: 1972
Make: Chevy
Model: K20
Engine Size: 403
Refrigerant Type: TBD
Ambient Temp: NA
Pressure Low: NA
Pressure High: NA
Country of Origin: United States

Hi,

I have everything working on my restored 72 chevy truck except the AC. I have read several posts and I think I'm ready to try to convert the AC system to operate on R134. I live in MN so its not hot here all year long. this is what I have acquired for the conversion so far. I have a new dryer, expansion valve, hoses, and O-rings(suitable for R134). I have a good used compressor, original evaporator, and condenser. I read some time ago in this forum that I need to adjust the TXV valve? with a rubber tipped air gun set to 60 psi in and 26 psi out. I purchased a flush kit and I will flush the evap and condenser with mineral spirts and blow dry air after flushing. I have 11 0z of PAG oil that plan to pour into the compressor while rotating by hand. Then I assemble the system adding the new dryer and pull a vacuum for 20 -30 minutes shooting for 29in of vacuum. Add r134 (80% of spec. which I have in found in the repair manual). Do I add the R134 before I try spinning the compressor? I assume that since the system is under vacuum it will draw in the R134 easily? But I have never done anything more than add some R134 to a working system before.
Does this sound like a reasonable plan?

94RX-7 on Tue June 11, 2013 8:11 PM User is offline

I think you mean adjust the POA, not the TXV.

The compressor should have a plug on the body that will let you drain oil from/add oil to the crankcase.

You might also consider changing the shaft seal on it to the modern double lip type if it hasn't already been done.

iceman2555 on Wed June 12, 2013 12:16 AM User is offlineView users profile

Do not flush with mineral spirits...you can not get the stuff out of the system.....residuals will contaminate your new lubricant and result is a decrease of compressor longevity. Mineral spirits will not and can not be removed without flushing with an additional chemical to remove the mineral spirits.

A suggestion would be to stay with R12. Your system will perform better and probably increase your satisfaction. Also change the shaft seals it will save the inherent problem of seepage around the shaft seal. Just my $.02 worth.

-------------------------
The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

Buds 72 K20 on Wed June 12, 2013 10:35 AM User is offline

Quote
Originally posted by: 94RX-7
I think you mean adjust the POA, not the TXV.



The compressor should have a plug on the body that will let you drain oil from/add oil to the crankcase.



You might also consider changing the shaft seal on it to the modern double lip type if it hasn't already been done.

So I drain the old oil and fill the compressor with new oil and the oil stays in the compressor? I assume the seal you are referring to is the shaft seal behind the clutch?

Buds 72 K20 on Wed June 12, 2013 10:40 AM User is offline

Quote
Originally posted by: iceman2555
Do not flush with mineral spirits...you can not get the stuff out of the system.....residuals will contaminate your new lubricant and result is a decrease of compressor longevity. Mineral spirits will not and can not be removed without flushing with an additional chemical to remove the mineral spirits.



A suggestion would be to stay with R12. Your system will perform better and probably increase your satisfaction. Also change the shaft seals it will save the inherent problem of seepage around the shaft seal. Just my $.02 worth.

What is the additional chemical? I could flush with isopropyl? Using R12 would be ideal but I thought it was not available? Since you suggested using R12 how does one buy it?

iceman2555 on Wed June 12, 2013 6:15 PM User is offlineView users profile

Alcohol will not remove the residual chemicals. DuraFlush II would be a good choice. It evaporates quickly and may not remove serious debris, but would be good for cleaning the mineral spirits from the system.
R12 is available, but one must be certified to purchase or buy from non licensed sources. Check local repair shops for possible recharge cost.

-------------------------
The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

Dougflas on Wed June 12, 2013 6:25 PM User is offline

Pulling a vacuum for 20-30 minutes is not long enough. If you don't have a micron guage hooked up, at least pull the vacuum for a few hours; over night is better.

Buds 72 K20 on Thu June 13, 2013 12:34 PM User is offline

Quote
Originally posted by: iceman2555
Alcohol will not remove the residual chemicals. DuraFlush II would be a good choice. It evaporates quickly and may not remove serious debris, but would be good for cleaning the mineral spirits from the system.

R12 is available, but one must be certified to purchase or buy from non licensed sources. Check local repair shops for possible recharge cost.

I did not know that I could get my R12 system recharged! So it should be even easier. If I can find a shop to recharge my system with R12 do I need even need or want to add PAG oil? Can I just connect everything properly and let the shop recharge my system with R12?

wptski on Thu June 13, 2013 3:19 PM User is offline

Quote
Originally posted by: Dougflas
Pulling a vacuum for 20-30 minutes is not long enough. If you don't have a micron guage hooked up, at least pull the vacuum for a few hours; over night is better.
Seems like there are differences of opinions on that here:

Evacuating and Charging

94RX-7 on Fri June 14, 2013 12:38 PM User is offline

Quote
Originally posted by: Buds 72 K20

I did not know that I could get my R12 system recharged! So it should be even easier. If I can find a shop to recharge my system with R12 do I need even need or want to add PAG oil? Can I just connect everything properly and let the shop recharge my system with R12?

NO PAG OIL with R-12. Chemically incompatible. A giant mess will ensue. Use mineral oil only with R-12.

Your cost to re-charge with R-12 is gonna be pretty high since the system will need several pounds. I suggest you replace every seal in the system (and be sure to use an updated design shaft seal) so that it holds onto the charge for a long, long time.

mk378 on Fri June 14, 2013 5:26 PM User is offline

Always static test an R-12 system with some other gas (nitrogen and/or R-134a) before charging with R-12. Static test means do not run the compressor, so it won't matter that the oil may not be compatible with R-134a.

Ester oil (POE) can be used with either refrigerant, but that does NOT mean that you can mix them. To convert / revert you will need to have all the refrigerant removed then charge with the other one. This is a physics issue as well as regulatory. Mixtures of the two refrigerants actually perform WORSE than either one alone.

Edited: Fri June 14, 2013 at 5:27 PM by mk378

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