I posted this chart (http://dodgeram.org/tech/repair/HVAC/R134a.htm) in another thread regarding an AC Problem, Well I got my AC Working, I am just worried about my pressure, any HVAC guys answer please. on this chart is says at 75 degrees Farenheit the LOW-SIDE pressure should be at 78.7 PSI, Is this true. the reason I ask is, on my LOW-SIDE tempature guage anything above 65 PSI is in the RED/DANGER zone.

I got my AC working, well I will know for sure in the next couple days if it is still working. But I am worried that there might be too much pressure and it might result in damage.

Can anyone with a working AC check their LOW-SIDE Pressure or anyone knowing about HVAC system let me know if this is right.
@ 85 degrees farenheit my pressure is about 70 PSI, the chart says it should be at 95.3 PSI, should I add more charge to bring it up to this?

Hey DK

The temps and pressures in the chart are most accurate for a system that is sitting - compressor not running. so on a hot day, the pressures will be a little higher than on a cool day. The equivalent for R12 is about 1 psi per degree F. The pressures for other gasses are a little different.

If the running low side pressure is 30 or 35 psi, then the temp in the evaporator/ducts will be around 40 degrees F because of the heat transfer and distance from the gauge.

If you look at the high side pressure and take a temperature reading of the line by the gauge connector you will likely find that they are close too. check back to the chart.

It's all based on boyles law or charles law or some other law named after some old guy -(older than me anyway):rolleyes:.

The amount of charge installed in the system should be based on the weight called for in the specs. if you over charge enough there is a slight chance that the compressor will take a gulp of liquid refrigerant and lunch its self.

So long as the duct temp is sitting cool enough and all the controls and flaps are working, you should be fine.

Watch the frost on the low side pipes that go to the compressor after the AC has been operating for some time. The higher the charge, the closer the frost will get to the compressor (relative humidity will affect this too).

I don't have gauges to check actual pressures. even then, our temps and humidity is different from yours.

Hope that helps some

JD

My Clutch is engaged all the time now, since the I add some more charge to the system. Should I test it with the engine off?

Sorry for the slow response. We've been away for the day.

Check the pressures with the engine running. The low side pressure should be in the low 30's just befor the clutch disengages. The pressure then will rise and the clutch will re-engage.

Please tell us how much "freon" you have added to the system.

The frequency of the cycle will depend somewhat on the temperature and humidity at the time but the clutch should not be engaged all the time. That suggests that there is not enough "freon' in the system. Thats the problem with just topping up and not starting with an empty, evacuated system and then weighing out the amount you install to fill it.

Check the sight glass if there is one. You should see a flush of bubbles go thru it around the times that the clutch cycles off/on.

JD