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AC high side low side pressure

A

aeidian

New member
99 GTP 3.8 Supercharged.

Bought a salvage compressor, gauges, vacuum pump, pag oil with uv dye, new seal kit. Vacuumed the system down, found a leak on the high side port, replaced it and the low side valves (that high side was a ***** to get out, I thought I had to hold the bottom nut and turn the top nut and nearly twisted the damn line off before I figured out just the top part unscrews) and revacuumed.


Didn't see any leakage on the gauges. High side did continue to "suck" after the high side gauge line was taken off. I could put my finger on it and the vacuum would grab my finger. Thought that seemed odd but didn't notice a leak on the gauges so I proceeded to add freon.

It took nearly the whole first can before the ac compressor even kicked on. I was using one of those blue/green/yellow/red gauges you get from the retrofit kits at the parts store because I didn't have a can tap for the manifold gauges yet. Took the whole can and let it run for a bit, was still in the green.

Decided I should go get a can tap, came back and added the second can. Added half a 3rd can, vent temperature inside the car with windows down and ac on max was about 66F with an outside temperature of 95-100F. PSI readings were 40-50 low side (mostly 45-50) and 250-300 high side (mostly 250). Let it run for a bit psi stayed around those numbers.

Vent temp never dropped below 66F. I haven't actually driven the car because I've still got to replace the oil pan gasket and just got the valve covers done today, and I know going down the road the ac works differently than just sitting there, so I don't know if the vent temp will drop, but its higher than the 45 to 55 temp everyone says it should be. Since I'm pretty far up the low side pressure I'm hesitant to add anymore freon. Is the low side too high? Is the high side too low?
 
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Couple things to consider:

1. You installed a used compressor. Why would you assume the efficiency be that of a new unit?
2. Your pressures are fine. Don't mess with it anymore.
3. Did you pull it down with oil in the system? This will get rid of moisture.
4. When running the system, were you pulling 100% outside air? Cannot achieve that kind of temperature differential unless recirculating the air.
 
Rico said:
Couple things to consider:

1. You installed a used compressor. Why would you assume the efficiency be that of a new unit?
2. Your pressures are fine. Don't mess with it anymore.
3. Did you pull it down with oil in the system? This will get rid of moisture.
4. When running the system, were you pulling 100% outside air? Cannot achieve that kind of temperature differential unless recirculating the air.
Click to expand...


I didn't consider the efficiency of a used compressor to be that of a new unit or not to be of a new unit. Every unit is new until used, right? I was questioning if something was off, and your 4th point logically makes sense now, I'll have to recheck with the windows closed, I didn't think about that. I did pull it down with oil in the compressor. I poured out what was in there, which was less than an ounce, and added 2oz of PAG 150 with UV dye, no leaks detected with UV light. Thanks for making the puzzle pieces fit.
 


AC Systems can be quite finicky. Generally 2 Cans Freon and 1 Can PAG-100 is plenty. Others may disagree but you are slightly overcharged. Low side is about 10/PSI too high and High side should float 230 +/- 15 At idle. You might find as you bring the RPM's up. Your high side pressure will climb too high and the compressor will shut off.
 
Brian99SE said:
AC Systems can be quite finicky. Generally 2 Cans Freon and 1 Can PAG-100 is plenty. Others may disagree but you are slightly overcharged. Low side is about 10/PSI too high and High side should float 230 +/- 15 At idle. You might find as you bring the RPM's up. Your high side pressure will climb too high and the compressor will shut off.
Click to expand...

Can I remove some of it without evacuating all of it? Just bleed off a bit by opening the manifold gauges or do I absolutely have to evacuate and vacuum the system and recharge?
 
I agree on you being a little high. However I'd suggest looking at the chart in the FSM that shows pressures with temps and humidty in the equation. Those are factors.

As for the temp.. 66F is good at 95F. The FSM says that a 30 degree delta is all you should ever expect.
 
BillBoost37 said:
I agree on you being a little high. However I'd suggest looking at the chart in the FSM that shows pressures with temps and humidty in the equation. Those are factors.

As for the temp.. 66F is good at 95F. The FSM says that a 30 degree delta is all you should ever expect.
Click to expand...

I've been called alot of things, being a little high was never one of them! Gonna bleed off a bit and take for a ride next week and see how it does. I can just add more if I feel like it needs it after that.

Sent from my SCH-I405 using Tapatalk 2
 


Took the car for a ride tonight since I got most of the rest of the work finished. The dash said the external temperature was 64F, but I know that's not right. Weather channel lists the temperature as 83, but it might be mid 70s, definitely not 64. Cruising down the road the dash put out between 44-46F with recirculation and set on 60F. Since I remember reading that's right in the range I want, I suppose I'm fine. I'll have to test it again tomorrow when the outside temperature is around 100F to make sure.
 
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