1990 Q45 / G50 A/C problem

[Amesdude25]

Hi all,

So now that the major mechanical stuff has been taken care of I've started working on the minor stuff like A/C. I knew the last owner and know that my car hasn't been charged in a decade. So my dad and I charged the Q a couple of weeks ago with standard R12. There are no major leaks that we can detect, just low from years of not maintaining proper charge.

So we charged her (she took two cans) and the A/C works great at idle and around town most of the time. But after awhile around town and always on the freeway the cold air is no more and just outside temp air comes in.

I did notice that the compressor was coming on and off as I think we might have over filled it. So I let a little out and know the compressor stays on. I was wondering if it could be overcharged? My dad doesn't think so though.

I'll post the actual psi for high and low later as I'm at work but if memory recalls. Low is around 50 - 60 and high is around 100. We actually had a third can we were starting to put in as the high was only at 90 psi and had to stop as it suddenly jump to 150+ psi. That’s when my dad said it was full. Good thing the Chevy uses R12 as well so I did waist any.

My dad is an old time master mechanic but hasn't work on cars professionally for some time and mainly with american cars.

Could the compressor just be tired and needs to be replaced, or the expansion valve? There are no air bubbles in the view. I'm leaning that we overfilled it but wanted to get some feed back before I let more out.

Thanks,

Danniel

[Q45tech]

The R12 system holds 2.5 -2.7 pounds if properly vacuumed down.

Your FSM deveotes 124 pages to HVAC system...........in minute detail.

[qship96]

ALL a/c diagnostic testing is useless unless you have the PRECISE amount of r12/134 in the system........and the ONLY way to determine that is by a proper recovery/vacuum down/and refill using accurate scale to the exact amount factory speced.Topping off from a can is a sure recipe for inaccuracy,resulting in many incorrect conclusions regarding problems with components of the ac system.

[Amesdude25]

Thanks guys,

I was just chatting with my dad and he said it took 2lbs (2 can's) and it could have air even though the spy glass doesn't show. He's wants me to take it down and vac and replace... I'll let you know if it works.

Thanks!

[qsiguy]

Unless R12 is way different than R134a than your high pressure is way too low. The low pressure side should be around 50 PSI and the high around 300 PSI. This is what it is on my '94 with R134a. Can someone confirm the high side pressure on R12 systems?

[Q45tech]

R12 IS VERY DIFFERENT FROM r134a..............................28-32 psi low and much much less -------------------------never over 230 psi high.

Your r134a has problems if 50 psi is the running on the road low psi or 300 psi is high:"With R12 systems, high side pressure is usually 1.8 to 2.1 times ambient temperature. That means on an 80 degree day, with moderate humidity, we would expect to see between 144 to 168 PSI on the high side. On hot humid days (with R12), you could say ambient temperature plus 100 PSI., and be pretty close.

With R134a it's common to see high side pressure between 2.2 and 2.5 times ambient temperature. On that same 80 degree day we would see between 176 and 200 PSI on the high side of an R134a system. "