AC Question - pressure too high?

[Pewter Sonoma]

The Oldsmobile's AC hasn't been very cold so I figured it needed a refill of R-134a. The kit I have has you test the systems' PSI before adding adding any refrigerant. My system is at 48psi, and it appears that's higher than the recommended pressure of below 25 psi for refilling.

From what I have read, the normal pressure is in the range of 30 psi.

So my question is - what do I do? The system is working (compressor clutch coming on; cold air blowing out), but it's not as cold as my other cars. Does the system still need a refill, even with the elevated pressure? If not, how do I make the air colder?

As is, the camaros' AC is significantly colder (approx 20-30 degrees F) than the oldsmobile.

[dfoulk]

If you hook up gauges to the high pressure side and low pressure side, you will get pressure that constantly varies according to temperature and the cycling of the compressor when the engine is running. If that was static pressure with the engine off, I have seen it as high as 60 psi. With the engine running, typical numbers might be something like 30 psi on low side / 250 psi on high side.

If it was me, I would put a thermometer in the center vent and close the other vents. With the AC on recirculate, fan on high, and an idle speed of about 1500 rpm, check the temp after waiting about ten minutes for everything to cool off. The cheap thermometers you can buy at Pep Boys have a blue zone marked on them at about 50 degrees F. You can then add refrigerent a little at a time until you see the temp cool down to the blue zone. Just be sure you hook up to the low pressure side. Those small cans of R134 will explode if hooked to the high pressure side. Also hold the can upright so the refrigerent goes into your system as a gas. Upside down feeds it in as a liquid which could lock up the compressor unless the the low side hook up feeds through the accumulater before the liquid can get to the compressor.

[Pewter Sonoma]

The 48psi was measured on the low pressure side with the car at idle, AC on, fan full on.

Thanks for the tips about the can orientation...

Should I add more R-134a, or could there be another reason the temperature is not super cold, but the pressure be higher than 30psi?

[dfoulk]

If it used to be cold and now isn't and no one has worked on it, it can't be over charged. It is possible to over charge one though. If you think it is overcharged, try bleeding R134 out a little at a time to see if it gets colder. It is possible to have high low side pressure due to a blockage. If that is the case, it would most likely need the orifice valve replaced. I am assuming it is an orifice valve system since that is what most newer cars have. I haven't seen one of the old style valves that actually opens and closes in a long time. The orifice valve does the same thing without moving parts, just a tiny hole in it. That tiny hole is what will stop up.

[Pewter Sonoma]

If it used to be cold and now isn't and no one has worked on it, it can't be over charged. It is possible to over charge one though. If you think it is overcharged, try bleeding R134 out a little at a time to see if it gets colder. It is possible to have high low side pressure due to a blockage. If that is the case, it would most likely need the orifice valve replaced. I am assuming it is an orifice valve system since that is what most newer cars have. I haven't seen one of the old style valves that actually opens and closes in a long time. The orifice valve does the same thing without moving parts, just a tiny hole in it. That tiny hole is what will stop up.

I'll bleed it off a little tomorrow and see if the pressure goes down. I might also add a little and see if I see any differential in pressure or temp.

What could get in the system to cause the valve to stop up? Thanks again for the tips.

FYI - I've owned this car for over 5 years and I've never had the AC system worked on or refilled - hence the reason I figured it needed a refill. I was a little suprised to see the pressure so high, becuase rational thinking would make you believe it would have been low considering the time it was last charged. It's a 2001 model with 141,000 miles.

[disneyd]

I'd go to Harbor Freight, buy a cheap set of AC gauges, and see what both the high and low pressure sides are running at. Just looking at the low pressure side isn't going to tell you the whole story. Your HP side might be too high or low when the compressor is running... indicating a charge problem (low or high), a compressor issue, or a possible blockage somewhere.

http://www.harborfreight.com/a-c-manifo ... 92649.html

[dfoulk]

What could get in the system to cause the valve to stop up?

When recharging, you can get moisture in the system causing corrosion. Particles from hoses, O rings, and other seals can also cause problems.

Could the door between the AC condensor and the heater core be blocked open or open due to a vacuum leak? If you run the fan without turning on the AC, do you get hot air?

[2fast4me]

Receiver dryer's are very good at shedding their desiccant and blocking the expansion valve, however that usually causes high head pressure and low pressure on the low side. Both high and low running pressure, and static pressure (not running) will vary depending on the temperature of the day.