Automotive Air Conditioning Information Forum

I've been struggling to figure out why my AC performance is abysmal. Need help diagnosing what the problem is.
1988 Mercedes 300TE.

Ambient 105F.
Idle low: 55psi
2000rpm low: 28psi

Idle high: 350psi
2000rpm high: 360psi

Idle temps are 60F, driving about 50F (in 105F ambient)

I have vacuumed down using my HF pump to approx 29mmHg, charged with 24oz refrigerant. Spec says to use 32oz...but I can't get there with pressures this high already.

Condenser, expansion valve and receiver/drier are all new. I also installed high flow dual aux fans and have them on toggle switch, so airflow is not the problem.

I keep getting told I'm overcharged on other forums with no help -- I'm not overcharged with only 24oz. I even tried using r152a as the curve is closer to R12 and pressures were still high.

What diagnosing can I run to find the problem?
Some ideas I keep running across are too much oil in the system or trapped air...any thoughts or other ideas?

32 oz was for R12 right? I realize you have a new condenser and fans but did you try to mist the condenser with a water hose? IF psi drops a lot, you could still have air flow problem. 105 ambient with vent of 60 is not that bad. Does that model have a heat exchanger in the high side lines?

Dougflas wrote:32 oz was for R12 right? I realize you have a new condenser and fans but did you try to mist the condenser with a water hose? IF psi drops a lot, you could still have air flow problem. 105 ambient with vent of 60 is not that bad. Does that model have a heat exchanger in the high side lines?

36oz for R12 and spec says to charge with 10% less r134a so I am quite undercharged and that is why I feel like it struggles most at idle. If humidity goes up I can easily get 70F coming out the vents at idle...

Not sure what you mean by heat exchanger, it has condenser evaporator drier expansion valve and hoses /w fuel cooler. Very straight forward.

I have not tried misting the condenser, but what will that prove when I already have a functioning fan clutching pulling and two Spal HD aux fans on high speed?

Driving at speed doesn't reduce high side pressures, so I don't think it's an airflow issue. If I put in all 32oz the pressures creep up to 400psi which makes the condenser extremely hot and that's obviously really off.

Tell us a little more about the New Condenser.

Is it a parallel flow unit? Tube & fin? OEM replacement?

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Regular tube and fin, OE replacement. Parallel flow was not available for this model and I wouldn't even consider a retrofit to PF until I can resolve the high pressure while being undercharged on the stock unit.

Air powered vacuum pump?

Oil charge when parts were replaced?