Mechanics

AC DOESN'T WANT TO TAKE A CHARGE

1972 Oldsmobile Cutlass • 223,000 miles

AC hasn't been used for a few years, as charge slowly leaked out.
When I started work on it and pushed in one of the charge valves there was a little burst of air, so it did hold something.
I removed the condenser and had it cleaned and tested at radiator shop. OK.
Put in new receiver-dryer.
Put new valve cores in high and low ports.
Put new R-D to POA hose as original was frozen to R-D fitting and broke.
I disconnected super-heat wire.

Put vacuum pump on system and it pulled to about 25". When I closed valves, it held the vacuum for at least 30 minutes.

I have several old stock drums of R12 Freon, so I am recharging with that.

Work being done at about 75 degrees outside temp.

After closing valves to gauge set, I attached Freon. Opened and cleared line.
Then opened low pressure valve (going to POA) to charge.

Low pressure gauge jumped to about 85 psi.

Started engine, turned AC on, temp to cool, fan on high.

Drum was sitting on scale to watch charge.

After 10 or 15 minutes, there still was no change in weight, or change in discharge temp.

Briefly, closed low valve and opened high side to try that. Gauge also went to about 80 psi. Didn't make any difference.

Compressor clutch is engaged, and you can hear compressor working. Sounds normal.

Tried another 10 or 15 minutes on low side. Still nothing.

Disconnected everything. I thought maybe new valve cores weren't opening, but when I pushed in pin there was a discharge under pressure, so I think they are working.

What might be the problem?

Thanks

Avatar
Srbz
June 19, 2012.




What were the pressures? How much did you put in the system? Overcharging will never produce cold air the same as under charging.

Did you replace the expansion valve and the screen in the line? The POA valve may also be seized which was common in the old days.

Roy

ASEMaster6371
Jun 19, 2012.
Which pressures?
When "charging", the pressure was 85 psi.
As far as I can tell, little to nothing went in.
Tank weighed 28 pounds when started and pretty much the same when done.

I did not replace the expansion valve.

Tiny
Srbz
Jun 19, 2012.
The high and low pressure. We need those readings when running.

Charging pressure is only the pressure of the freon going into the system, not the operating pressure.

Roy

ASEMaster6371
Jun 19, 2012.
Ok.
I'll get that tomorrow morning
Thanks
AD

Tiny
Srbz
Jun 19, 2012.
Ok. I need running pressures.

Roy

ASEMaster6371
Jun 20, 2012.
Running pressures. Outside temp 65 degrees, AC on high and cool.

The low side is about 1 psi. The high side 40 psi.

As I mentioned above, it looked like hardly any refrigerant entered system.

Thanks

Tiny
Srbz
Jun 20, 2012.
Yep, you are right. Are you sure it did not leak out from yesterday?

Roy

ASEMaster6371
Jun 20, 2012.
I put the Freon tank on a scale.
When I started (trying to) recharge, it weighed 28 pounds.
When I stopped, it weighed at least 27 1/2 pounds.
So, not much went in.
All that "leaked" would have been from removing and attaching the gauge set.

Do the pressures tell you anything?
Why won't it take the charge?

Thanks

Tiny
Srbz
Jun 20, 2012.
Could be a schraeder valve issue. Could be your gauge set as well.

Does it have a site glass on the dryer to see if it is circulating?

Is the compressor on? It has a thermal limiter switch on the compressor harness that should blow if the compressor runs and there is no freon.

Roy

ASEMaster6371
Jun 21, 2012.
As noted above, I replaced schraeder valve cores and the compressor is running.
I unplugged the superheat switch so the thermal limiter wouldn't blow, as the manual states.
RD does have sight glass and nothing going through.

The gauge set does appear to be working. It goes down with vacuum and up with pressure. Pressure readings have ranged up to 90 psi.

Tiny
Srbz
Jun 21, 2012.

AD