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A/C stopped

rockfoot on Sat September 20, 2008 11:56 AM User is offline

Year: 1995
Make: Mercedes
Model: 300D
Engine Size: 3 liter
Refrigerant Type: 134A
Ambient Temp: 75
Pressure Low: 0
Pressure High: 0
Country of Origin: United States

My A/C stopped working yesterday morning after no warning at all... it worked very good the day
before. I jumped out the low pressure switch and the clutch engaged. The inside blower works. The aux fans
did not come on. I had problems with the aux fans before but they never prevented the A/C from working. It would just cause the engine to run a little hotter when idling... I hooked the gages up on the hi side and the
low side and there was "0" pressure on the hi side and a vacuum on the low side. Wasn't real sure what was going on so I got my jug of 134 to see if it would take a charge... as I started to get pressure on the hi side (40psi), the low side started coming up a little as it should. When I secured the jug valve, the low side went back to a vacuum and the hi side went to "0"... What is happening?? If it was the expansion valve plugged, wouldn't the hi side show a hi pressure??

mk378 on Sat September 20, 2008 12:32 PM User is offline

Zero pressure all of a sudden of course means there's a major leak. You may not be able to add refrigerant as fast as it leaks out.

Inspect for blown hoses, spots worn through a metal line or a hose, holes in the condenser due to rocks, etc. If you don't see anything obvious, with the engine off put a little R-134a in and listen for it to hiss out. There might be a relief valve on the back of the compressor or the high side line that has opened and did not re-close.

After repairing the leak, you should also change the drier being that it's 13 years old. Then follow standard procedure to evacuate and recharge. Charge by weight to the specified amount, there is usually a sticker on the car.

Edited: Sat September 20, 2008 at 12:38 PM by mk378

rockfoot on Sat September 20, 2008 12:35 PM User is offline

I agree with that logic. I will put the vacuum pump on it and see what happens....

Edited: Sat September 20, 2008 at 12:35 PM by rockfoot

rockfoot on Sat September 20, 2008 2:07 PM User is offline

Well, I went out there to evac the system and the hoses would not fit the vacuum pump... so... just for grins, I hooked up the hi and lo side to check it one more time... immidiately, the hi side was hissing like crazy.. bad adapter fitting/"o" ring. I didn't hear it before cause the engine (diesel) was running... I opened up the jug of freon for about 1 minute (40-50 psi), then checked the continuity across the LP cutout switch... good to go... started the engine and the A/C is blowing cold... Put a little more in and took her for a test ride to the auto parts store to get the correct adapter fitting for the vacuum pump and a new hi side quick disconnect... still don't know why I was showing a vaccum before... am a little dubious and plan to evac and recharge system.

tony1963 on Sun September 21, 2008 2:14 PM User is offline

I would be willing to bet that you have an evaporator core leak. I've changed several of these over the years in this model and you have to pull the entire dash assembly, crash bar and climate control box to do the job.

I once had the identical vehicle that had an evaporator leak so bad that when you tried to pressurize the system, you could hear the refrigerant hissing in the vents. Obviously, I replaced the evaparator, drier, expansion valve, o-rings, etc.

It's a big job but you can do it yourself if you have plenty of garage room and sanity.

Grove Automotive Group, Inc.

An Alabama Corporation

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