Another air conditioning question Low = 34 High = 48

[dsagers]

Searched and read a bunch of threads and now I want to run these numbers past any professional AC guys, or anyone with experience.

1992 Q45 88K miles.

Last year the AC worked great. This year it will be slightly cool when idling, but when I drive down the road the vent temps heat up to what feels like the outside temp.

Put the gages on this afternoon.

Outside temp 70 F

Idle:Low = 30 High = 48 Vent temp is slightly cooler than ambient

At 1500 RPMLow = 34 High = 48 Vent temp starts to increase.

Car ran for 10-12 minutes before I recorded the pressure.

Over the last two weeks I have added two 12 oz cans of R12, and the sight glass still has bubbles in it.

The low side seems a little high, but not much and the high side is really low. Considering it worked last year and this year I have added two cans of freon, does this indicate a weak compressor?

Where else should I look?

[Q45tech]

Lately we are seeing ABNORMAL OLD Q with low miles but high age so difficult to correlate since all my data assumes 15,000 miles per year not 5,000.................

Since the 1950's R12 vehicular AC systems have shown the correct pressures for proper functiong. High pressure discharge should be 100-200 psi depending on ambient temp.

Lower than the appropriate psi almost always indicates a compressor failure WHICH IF NOT DETECTED very early as it just drops 10-15 psi with flood the system with contaminations rwquiring a almost total system replacement and or flushing IF as new cooling is expected and not 70-80%.

Beautifully explained in FSM.

I'm on compressor number 3, The new ones and Nissan only remands usually last 7 years +.

The above assumes you spend for periodic mainteance on AC system with oil changes at midlife most do nothing, thus 7-8 years on a new unit. unfortunately remanns are never as good as brand new but you can stretch them out to 7 years if you try.

[dsagers]

Q45tech, thanks for the great answer.

With my high pressure so low, do you think my compressor has failed to the point where I need to flush the system for containments?

Any thoughts on adding a filter in the intake hose to the compressor?

I have access to several more pounds of R12. What's your opinion of staying with R12 or converting to 134A in these older Q's?

[elwesso]

I almost wonder if maybe one of the reed valves (or whatever they call them) is stuck inside the compressors. Id think a compressor will still be able to put out more than 48lbs even when its ultra weak!

[maxnix]

if you have to replace the whole system, then R134a is definitely better long term. Not much if anything is shared between the R12 and R134a systems.