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Replacing an original A6 compressor with an S6 and now less cool


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My 1980 Avanti had the original A6 compressor. It was converted years ago to R-134a. It cooled well but it was leaking around the front seal. I replaced it with an S6 from Old Air products. It was supposed to be a direct replacement for the original and it did bolt right up.

But now, it does not seem to cool near as well as the other regardless of the amount of 134a. It pulls the low side down to almost zero and the high side goes to around 225 PSIG.

I would normally expect to see 20-30 pSIG on the low side but if i try to charge it more to achieve that, the high side may hit close to 300 PSIG.

Any ideas?

Thanks

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Did you replace the receiver/dryer or whatever is used in its place?  Anytime the system is opened up the dryer should automatically be replaced.  The expansion valve should be looked at as well...if that clogs the high side hose will literally explode off the compressor...no need to ask how I know that.

That being said...the GM A-6 compressor...while large and heavy...is an exceptionally good piece of cooling equipment.  I've heard people say it can damn near cool a house.  Replacement compressors may not cool as well even though they may be lighter and smaller.

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45 minutes ago, Gunslinger said:

Did you replace the receiver/dryer or whatever is used in its place?  Anytime the system is opened up the dryer should automatically be replaced.  The expansion valve should be looked at as well...if that clogs the high side hose will literally explode off the compressor...no need to ask how I know that.

That being said...the GM A-6 compressor...while large and heavy...is an exceptionally good piece of cooling equipment.  I've heard people say it can damn near cool a house.  Replacement compressors may not cool as well even though they may be lighter and smaller.

Yes i did. I am about read to go back to a rebuilt A6. Very frustrated. Wither difference in high to low side pressures, I would think this S6 should cool quite well.

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I am running an S6 from Old Air Products with R-134a in my '78.  Otherwise, the rest of the system is still factory stock, which was originally R12.  That said, the system cools very well.  I am no expert in A/C, but I am told that unlike the R12, the R134a is very sensitive to having the correct charge.  Too little or too much is bad.  Unfortunately, since it is a conversion, there is no sticker under the hood that would tell us the "proper" charge.  The shop that charged mine has the latest equipment and a very competent tech.  He took his time and charged the system in small increments letting it stabilize, checking the pressures and the temperature of the evaporator along the way.  The whole process took about an hour, but the results were very good. 

Might it be possible that there may be a problem with your expansion valve?  Again, I'm no expert, but wouldn't a restricted expansion valve cause the high pressure differential and poor cooling that you describe?

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Expansion valve appears to be working and with the old A6 compressor all worked well.

Do you know the temperature coming out of the vents?

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23 hours ago, pantera928 said:

Expansion valve appears to be working and with the old A6 compressor all worked well.

Do you know the temperature coming out of the vents?

The temperature out of the evaporator will vary with the ambient temperature.  During the charging process, we were seeing a temperature drop of about 30-35 degrees.

 

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3 hours ago, Jim78 said:

The temperature out of the evaporator will vary with the ambient temperature.  During the charging process, we were seeing a temperature drop of about 30-35 degrees.

 

Was that enough of a drop to make the car comfortable on a hot day?

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20 hours ago, pantera928 said:

Was that enough of a drop to make the car comfortable on a hot day?

Yep. 

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5 hours ago, Jim78 said:

Yep. Thanks. I will test more this weekend weather permitting. My general rule of thumb 75% of what was used with R-12. 20-30 psig at idle on the low and 2.5 times the ambient temperature in Fahrenheit which is usually 200-225 PSIG on the high side

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