Replaced A/C Equal Pressures no cooling - PeachParts Mercedes-Benz Forum

buddyligon · #1 05-01-2007, 02:25 PM

Finished replacing A/C compressor, Receiver/Dryer and Expansion valve (yes it was a pain as described in the forum) and after a good flushing, 134 oil correct amount, vacumed well. Reintroduced freon (134) and all seems top work as it should compressor engages aux fan turns but no cooling and the pressures equalizes around 95 PSI low and 100 PSI high and no more freon goes in after a can and a half. If I rev the engine a bit it goes to 75 and 110 psi. Since I have fixed another A/C system on a toyota (still working great after two years) and had help from a local mercedes repair person ( he lets me use his guages and vacuum pump) I hope and believe I did everything correctly as far as putting the system back together. I feel that the compressor is simply not producing pressure and the reason the pressure equalizes is it works its way through eventually. So after the initial can and half no more freon will go in as the compressor won't pull a suction to pull in freon and then increase the high side pressure. The other thought is the expansion valve is bad and just letting the flow through with no resistance? The compressor is a rebuilt unit and the expansion valve and dryer came from reputable source in AZ... Thoughts?

rrgrassi · #2 05-01-2007, 02:47 PM

Does the compressor's clutch engage? Have you checked all connections and fuses? I had a wire snap off on the compressor side and not know until I trid to run it. Ended up splicing it, and it has been fine ever since.

buddyligon · #3 05-01-2007, 03:15 PM

Yes clutch engages. Found and replaced a bad aux fan relay that wasn't working before tackling the A/C change. All fuses good. Compressor engages as soon as I started engine after first can gave the system 50 psi overall.

rrgrassi · #4 05-01-2007, 03:19 PM

That 50 PSI sounds too high with one can unless that was spread over the system before startingthe engine. Have you checked the rubber lines for kinks, and checked the metal lines to be sure they are not crushed closed?

With the compressor running, does the upper line running in front of the valve cover get cold, and the lines at the drier get warm/hot? The system should hold 3 cans.

How are the lines on the guages? I had a manifold stay closed, even though I had opened the valve to allow freon to flow. This was on a cheap K-Mart special set when you could by R12 w/out a license.

HowellK · #5 05-02-2007, 09:24 PM

Buddy,
I've been looking for an a/c thread like this.
Recently I recharged my a/c for the second time and it behaves like yours:
In the '85 300TD I put in a new compressor, drier, expansion valve, and freeze-12 after flushing and then evacuated and all; didn't cool; pressures were even at idle. I changed seals on the compressor (lots of threads on those seals) last week and put in 22oz of freeze-12, and I have 60psi at idle on high and low; then at 1500rpm I have 40psi low and 85psi high side!! (ambient 80). I feel as you do that the expansion valve might not be working, but even at idle we should be getting a better low pressure reading. I know I need more freon, but the low pressure side doesn't want to take on more.
The fact that both high and low are even means that the compressor "sucks" but doesn't suck enough, right? It's that R-4 compressor again.
Is it holding pressure?
Is there some other test for the compressor??

JimmyL · #6 05-02-2007, 11:26 PM

Well, it sounds to me like the expansion valve has a clog, and won't let the freon "circulate". I had one do this on my wagon before I did my rebuild on it......
Have you checked to see if the lines to/from the expansion valve to the evaporator freeze up after a short time of it running? If not, run it and give that a look. Mine frosted over rather quickly.....

Shorebilly · #7 05-03-2007, 06:20 AM

Quote:

Originally Posted by JimmyL

Well, it sounds to me like the expansion valve has a clog, and won't let the freon "circulate". I had one do this on my wagon before I did my rebuild on it......
Have you checked to see if the lines to/from the expansion valve to the evaporator freeze up after a short time of it running? If not, run it and give that a look. Mine frosted over rather quickly.....

If your Expansion Valve is clogged you would get a high pressure on the high side and an abnormally low pressure on the Low Side.....if all else is working as it should.....that's why Industrial reefers have a "low pressure cutout" to prevent a vacuum from being pulled on the cooling coils.....

if the Expansion Valve, or anything else is causing a partial restriction....you will generally have Ice forming at and after the clog......

I would suspect the compressor.....maybe just a piece of scale or Teflon tape (this is one of the reasons that I dislike Teflon tape) under a valve.....is the compressor getting hot?? If your compressor is working the discharge to the condenser will get warm and the suction from the evaporator will get cool......if the suction valve is leaking the low side line just before the compressor will get warm/hot......

Did you evacuate the system before adding the refrigerant??

SB

Universal Reefer Tech w/ ASE Automotive Certification......among my other accomplishments......

vstech · #8 05-03-2007, 07:12 AM

equal pressure while running, can be only one thing. compressor.
like said above, expansion valve stuck closed will cause a vacuum, stuck open would still provide quite a pressure drop. sorry.
John

vstech · #9 05-03-2007, 07:16 AM

Quote:

Originally Posted by HowellK

Buddy,
I've been looking for an a/c thread like this.
Recently I recharged my a/c for the second time and it behaves like yours:
In the '85 300TD I put in a new compressor, drier, expansion valve, and freeze-12 after flushing and then evacuated and all; didn't cool; pressures were even at idle. I changed seals on the compressor (lots of threads on those seals) last week and put in 22oz of freeze-12, and I have 60psi at idle on high and low; then at 1500rpm I have 40psi low and 85psi high side!! (ambient 80). I feel as you do that the expansion valve might not be working, but even at idle we should be getting a better low pressure reading. I know I need more freon, but the low pressure side doesn't want to take on more.
The fact that both high and low are even means that the compressor "sucks" but doesn't suck enough, right? It's that R-4 compressor again.
Is it holding pressure?
Is there some other test for the compressor??

this is quite a different situation than the OP. your system does indeed sound like expansion valve problems.
it could be too much oil in the system, it could be blower motor issues, and it could be dirty evaporator.
I would start a new thread about this, and give more details on the issue, and what you have done.
John

buddyligon · #10 05-07-2007, 11:19 AM

Thank you for the information. I suspect a bad compressor. Didn't find any closed lines blockages just everything is clear with no restrictions when reflushing system and added note the system kept good pressure over the week no leaks but will replace the compressor, expansion valve and dryer again and flush since I don't want to take a chance the supposedly good compresoor sent particles through the system. I noticed the aux fan relay (replaced before starting endeavor made sure was good) clicking a lot with the fan coming on and off so I will also replace the thermo switch to the relay coming off the thermostat (85 apparently has two ways to activate the fan the A/C and thermostat)

DeliveryValve · #11 05-07-2007, 11:38 AM

One question, How much oil did you add? Too much will slug the compressor (because it can't compress the oil) and too little will burn it up. Also, make sure you flush it thoroughly to get all the old oil out.

vstech · #12 05-07-2007, 11:53 AM

good point rmarzan! a new compressor comes without oil, so complete oil charge would be needed, like 8 oz I think! especially if you flushed the coils and lines!
John

Kuhlrover · #13 05-07-2007, 03:42 PM

Howell,

In your post you said you installed 22 ounces of Freeze 12. This is not enough. For a W123 sedan, your system should hold 2.9 Lbs of Freon 12 which is 46.4 ounces. The coversion from Freon 12 to Freeze 12 is to use 10% less Freeze 12 or 42 ounces. Also, an R4 compressor holds about 6 ounces of oil.

TimK

carnut · #14 05-07-2007, 03:58 PM

Been my experience that rebuilders ship compressors overfilled with oil on purpose and the oil is drained and the proper measured amount is put in at the time of installation. Might be different now but when I was doing replacements the instructions always said to drain out oil and verify correct amount be added.

bfowler71 · #15 07-27-2012, 05:33 PM

Quote:

Originally Posted by carnut

Been my experience that rebuilders ship compressors overfilled with oil on purpose and the oil is drained and the proper measured amount is put in at the time of installation. Might be different now but when I was doing replacements the instructions always said to drain out oil and verify correct amount be added.

Buddt: I have the same problem on my 78 300cd. I have installed the same parts..100 pounds on both sides..wil not take gas. Compressor get very on low & high side connections. I THINK i have a bad rebilt 4 Seasons York compressor. let me know how you solved your problem.