R134a pressures too high

Friendly format provided to inquire about automotive a/c systems.
Archived Forum

Moderators: bohica2xo, Tim, Dougflas, HECAT

Ps2cho
Posts: 3
Joined: Mon May 15, 2017 11:39 am

R134a pressures too high

Postby Ps2cho » Mon May 15, 2017 11:46 am

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?
Dougflas
Posts: 174
Joined: Mon Apr 18, 2016 6:10 pm

Re: R134a pressures too high

Postby Dougflas » Mon May 15, 2017 6:25 pm

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?
Ps2cho
Posts: 3
Joined: Mon May 15, 2017 11:39 am

Re: R134a pressures too high

Postby Ps2cho » Tue May 16, 2017 7:13 am

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.
User avatar
bohica2xo
Posts: 205
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: R134a pressures too high

Postby bohica2xo » Tue May 16, 2017 10:51 am

Tell us a little more about the New Condenser.

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

.
Ps2cho
Posts: 3
Joined: Mon May 15, 2017 11:39 am

Re: R134a pressures too high

Postby Ps2cho » Tue May 16, 2017 9:32 pm

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.
User avatar
bohica2xo
Posts: 205
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: R134a pressures too high

Postby bohica2xo » Wed May 17, 2017 11:56 am

Air powered vacuum pump?

Oil charge when parts were replaced?

Return to “Automotive Air Conditioning Forum”