1993 W124 300D

Can an overpressurized A/C system cause the compressor to kick off?

I think that may be what my problem is.

I thought I had a bad fuse first but that day was the first very hot day around here.

I checked the pressure and it was over 100psi.

I also noticed sometimes when I revved the engine high the A/C would temporarily stop cooling.

If not, what else might I have going on?

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1993 W124 300D
-297K on the clock as I type this.

If its hot outside and the AC isn't running the low side can be that high. If there is an overpressure switch it will generally cause a cut out at 400 PSI or so.

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

The pressure? Would that be high side or low side? Compressor on or off?

It read over 100psi with the compressor off but the A/C switch was on.

It actually was pushing 120psi at one point.

I then proceeded to try to bleed off some on the side of the road and ended up bleeding it all off.

I have since been recharging the hell out of it to get it to cool better but this is my first summer with it so maybe that's as good as it cools in the summer.

It has been very hot and uncharacteristically humid here lately as well.

The pressure I read was the high pressure line where you recharge the system.

As I pushed over 65 in my effort to recharge the system, the compressor cut off and will intermittently come back on only to shut off shortly thereafter.

Once, it was running until I hit the throttle, if that's what it's called on a diesel, to raise the RPMs.

I decided to let it rest until I found out more and wasted any more refrigerant.

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1993 W124 300D
-297K on the clock as I type this.

With the compressor off, the refrigerant pressure varies as a function of temperature. As long as there is a drop of liquid refrigerant in the system, the pressure is constant at a given temp. Static pressure is of little value when attempting to diagnose an a/c issue.

In that case, the system should be evacuated prior to adding new refrigerant. Replacing the receiver/drier is also indicated.

OK, but it's basically acting like it was before I evacuated the system.

Do you have any idea what might be the problem?

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1993 W124 300D
-297K on the clock as I type this.

You need a good starting point to find out what is wrong. It sounds like you have been arbitrarily adding refrigerant in an effort to make it work.

Recover the refrigerant in the system, replace the dryer, and check for leaks. When you are absolutely sure there are no leaks ( pull a vacuum on the system through your gages, then shut off the valves and leave the gages connected overnight, if the gage readings have changed other than a small allowance for temperature, you still have a leak) Charge the system with the proper amount of refrigerant as (you are using R12 right!) and then you can see if it is operating properly.

An undercharged or overcharged sytem will not cool properly, and if you have a leak, chances are there is moisture in the system, which can freeze in the expansion valve and cause intermittent cooling.

Once you have no leaks, no moisture, and the proper refrigerant charge you can start diagnosing any issues, if you still have any.

Reading between the lines, I conclude:
1. You do not have a set of guages and are reading a single value from the top hose (low side).
2. At this point none of us can estimate what you may have in the system.
3. You need to follow the instructions (short, but not as thorough as others recommend) of the last poster, but first get a complete guage set to be able to connect and get readings on both high and low side as you do this work. You'll also need a vacuum pump.
4. You've got a significant amount of learning (do some searches) before you proceed.
5. You might be better off hiring this done unless you're will to learn how to do this properly.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html

It's R134a, not R-34.

Easy way to tell high side from low side. With the system fully functional, the cold line is the low or suction side. The hot lines are the high pressure or discharge side.

My '97 Nissan P/U came w/R134a from the factory. I'm thinking you could get cars w/R134a in '95.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

Thanks for pointing that out.

It is definitely R-134a.

The port I am using is definitely cold. There is some condensation near the port.

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1993 W124 300D
-297K on the clock as I type this.