A/C pressures?

[curmudge1]

copied from my reply in the Member's forum, to see if I could get an answer here:

All this A/C service talk made we want to do some tests to see if my a/c system was running at full capacity... a colleague has the A/C retrofit kit with gages, so we hooked up to my 1994 Blazer 6.5TD. It was originally R134a, no conversion.

We saw low pressure reading between 40 & 45 psi, and high pressure about 205 psi. So, can anyone tell me what these reading should be? How does one find out? I'd like to check my recently acquired 1999 Tahoe w/ 5.7gas, too. Would the specs be the same?

Thanks.

[morgan]

With electric throttle, it's hard to put fluid in at elevated RPM's, so just keep shaking the bottle.

I used one of those kits too, with the cheap gauge that has color coding sections. The low side should pull down into the blue or green area when the clutch is engaged.

In my case, I just dumped 2 cans of fluid into it, and it was at 55 deg F at the vent while idling in the driveway, but got down to 35 deg when I was going down the highway. It about froze me out of the cab!

Good luck. Send me a PM if you still aren't confident about it. I do it myself every year.

[kevin77]

You could check out a pressure chart at http://www.ackits.com/index.cfm?fuseaction=Chart

Reading the pressure correlates to the outside temperature - the hotter it is outside the higher the pressures. I seem to remember at about 70 degrees, my low side was running 35 to 40 psi and the high side just under 200 psi. That is a suburban with the rear air.

The other thing to consider is those pressures are suppose to be taken when you are running your air conditioning on high.

Kevin

[fastcat800]

I just tried to add refrigerant and the compressor would not kick in even after jumpering the low pressure switch with a can of R134 hooked up. I checked for power at the LP switch and there is none. I checked for fuses but only found the heater fuse that is for the blower, I think. Where does the power come from for the LP switch? Anything else I should look for?

[norm]

Try checking for continuity at your high pressure cut-out switch, too. other than that, you have to find the fuse and trace back till you find voltage.

[catmandoo]

dave you might try unhooking the battery cables,as sometimes on these units if you experience an a/c problem,it will act goofy and you basically need to reset it.usually when this happens the a/c lite will flash on and off.

[HowieE]

Dave
The power for the low pressure switch comes from 25 amp heater a/c fuse #12. From the fuse power goes to the the compressort control logic board in the heater a/c control module. There are several mechanical switches and a diode in the circuit. If you do not have power on the light green wire coming out of the control module or at connector C100, LH rear of engine compartment at bulkhead, to the low pressure switch I would look at the module and the diode in it.

[fastcat800]

Thanks guys, I will see if I can get to it today and try all of your suggestions.

[charliepeterson]

With these readings operating with a full charge they are too high. Is the compressor making any strange noises? Normal is Low side 20-30 and high side 150-160. To figure out the high side take the ambient temp in front of the truck and add 100 to it, do this out of the sun, this is the normal max. I would guess the compressor is failing. If you do swap it out, do the accumulator tank and orifice screen too.


"We saw low pressure reading between 40 & 45 psi, and high pressure about 205 psi. So, can anyone tell me what these reading should be? How does one find out? I'd like to check my recently acquired 1999 Tahoe w/ 5.7gas, too. Would the specs be the same?"