A/C pressures

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512Stroker

512Stroker

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I have an all stock component 1967 factory A/C system that has been converted to 134A
What pressures on both the high and low side should I be getting when the system is operating properly?
 
Depends on the temperature / humidity outside. Low side will be @30 to 35 High side @225 to 275
On a hot day High side maybe higher and you'll never get the Low side to 30
 
Good rule of thumb on high side with r134 is multiply ambient air temp times 2 and add 50 psi. So on 80 degree day, 210 psi high side is “ideal.” Imagine those as air quotes as every system is a little different and humidity will make a difference as well.
 
leechris81 said:
Good rule of thumb on high side with r134 is multiply ambient air temp times 2 and add 50 psi. So on 80 degree day, 210 psi high side is “ideal.” Imagine those as air quotes as every system is a little different and humidity will make a difference as well.
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Nice RoT
As you well now it is hot and humid here in MO
 
512Stroker said:
Nice RoT
As you well now it is hot and humid here in MO
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No doubt about the humidity. I converted the system in my ‘73 Swinger and even tinted the windows to help. Its year three and I’m still not happy. I want to be able to hang meat in there. It keeps it comfortable but one day I’ll win. Good luck!
 
If it's a hot and humid day, I've seen normal 134 temps as high as 350 on the high side and 150 on the low side. It just "depends".
 
If the low side line is sweating where it enters the compressor, you are pretty close to optimum.
 
FWIW Humidity has nothing to do with condenser pressure..... The condenser is not "wet" so there is no latent heat..... Only sensible heat.....
 
leechris81 said:
No doubt about the humidity. I converted the system in my ‘73 Swinger and even tinted the windows to help. Its year three and I’m still not happy. I want to be able to hang meat in there. It keeps it comfortable but one day I’ll win. Good luck!
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Did u change the condenser? Kim
 
oldkimmer said:
Did u change the condenser? Kim
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I did not. I have done dozens of conversions through the years and don’t change anything other than the fittings. Once I put the 134 in, I switch to the appropriate pag oil as well. I know not everyone will agree with this and I certainly know it’s not “by the book,” but I have had great successes.
 
You might check you heater valve & see if water is leaking through a lot. I have seen improvements from installing a manual shut off valve to positively stop all hot water flow to the ac box.
 
leechris81 said:
I did not. I have done dozens of conversions through the years and don’t change anything other than the fittings. Once I put the 134 in, I switch to the appropriate pag oil as well. I know not everyone will agree with this and I certainly know it’s not “by the book,” but I have had great successes.
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Ive did it b4 also. But I’ve had a couple stubborn ppl wouldnt change any other part. It made a big difference. Did u change the expansion valve. Kim
 
oldkimmer said:
Ive did it b4 also. But I’ve had a couple stubborn ppl wouldnt change any other part. It made a big difference. Did u change the expansion valve. Kim
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No on the expansion valve too. I did have the rubber replaced on my hoses while I had them off just as a precaution.
 
Mike69cuda said:
You might check you heater valve & see if water is leaking through a lot. I have seen improvements from installing a manual shut off valve to positively stop all hot water flow to the ac box.
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I actually found an NOS valve and replaced it some time back. It helped a bunch shutting the water off.
 
93ragtop said:
FWIW Humidity has nothing to do with condenser pressure..... The condenser is not "wet" so there is no latent heat..... Only sensible heat.....
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Absolutely wrong. Relative humidity has a LOT do do with both how cool and especially how DRY the air in the cabin gets. If relative humidity is above 60% and the ambient air temperature is in the mid to high 90s or more like here in middle Georgia, the system will struggle to get that 20* temperature difference BECAUSE there is so much humidity in the air. You seem to forget the A/C system also dries the air in order to make it easier to cool. The more humidity, the tougher the system's job. An A/C 101 course will clear that right up for you.
 
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Mike69cuda said:
You might check you heater valve & see if water is leaking through a lot. I have seen improvements from installing a manual shut off valve to positively stop all hot water flow to the ac box.
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Ordered 4 days ago a 5/8 zinc coated ball valve should be here tomorrow for installation.
 
I put 60 psi (@ 80F) low side at a fast idle in my 02 Silverado work truck, dont have high side fitting. It's got a leak they wont fix so I just fill with cheap Propane (poor mans R290!) and it cools down to 35F out the vents on high. R134 is almost as expensive per oz as Johnny Walker Blue out here in CA so I just let it leak good 'ol environmentally safe propane. Yeah, I've heard how 'unsafe' it is but most of us are driving around ~20 gallons of gas 2 inches from exhaust pipes and some is pressurized 55 psi inches from 500F exhaust manifolds. 60 PSI will last me 2 months before its unable to kick the compressor on.
 
pishta said:
I put 60 psi (@ 80F) low side at a fast idle in my 02 Silverado work truck, dont have high side fitting. It's got a leak they wont fix so I just fill with cheap Propane (poor mans R290!) and it cools down to 35F out the vents on high. R134 is almost as expensive per oz as Johnny Walker Blue out here in CA so I just let it leak good 'ol environmentally safe propane. Yeah, I've heard how 'unsafe' it is but most of us are driving around ~20 gallons of gas 2 inches from exhaust pipes and some is pressurized 55 psi inches from 500F exhaust manifolds. 60 PSI will last me 2 months before its unable to kick the compressor on.
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I don't use propane but I would tend to agree. I read the op's thread title and thought to myself, I would have to look the pressures up on a chart. Last week they were different than today. I only look at the pressures if there is a problem. The duct temp is what I look at.
 
RustyRatRod said:
Absolutely wrong. Relative humidity has a LOT do do with both how cool and especially how DRY the air in the cabin gets. If relative humidity is above 60% and the ambient air temperature is in the mid to high 90s or more like here in middle Georgia, the system will struggle to get that 20* temperature difference BECAUSE there is so much humidity in the air. You seem to forget the A/C system also dries the air in order to make it easier to cool. The more humidity, the tougher the system's job. An A/C 101 course will clear that right up for you.
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LOL..... You need to re-read my post. I said CONDENSER, not evaporator......
You may want to read up on Latent heat vs Sensible heat.
Humidity has nothing to do with the heat removal of the condenser or for that matter the radiator. The only heat removed is sensible heat and no latent heat.
Latent heat is only in play when something sweats, ie: human body, or evaporator.....
High pressure reading will not change due to humidity.
 
But the condenser is removing the latent heat from the refrigerant. That's how it got it's name.:lol:


Sorry, couldn't resist. Carry on. I'm staying out of this one.
 
toolmanmike said:
I don't use propane but I would tend to agree. I read the op's thread title and thought to myself, I would have to look the pressures up on a chart. Last week they were different than today. I only look at the pressures if there is a problem. The duct temp is what I look at.
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Mike you right
My system will only cool down to 50*F at the vents. That's way I was looking for pressures.
All the charts I found were for R-12 my has been converted to 134A
I thought this may make a difference, it didn't.
I going to dig in to today with a real set of gauges at a Buddy's shop.
I will report back
 
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