A/C compressor pressure too high?? - PeachParts Mercedes-Benz Forum

lsmalley · #1 06-24-2011, 08:02 PM

took my car in to be serviced for a/c today and the guy told me that I need a new compressor because the pressure was too high from the compressor on the high side? I noticed that my a/c isn't as cold during the 110 degree weather here, but when I'm driving at 40 mph + it seems ok or even when it cools off a little the a/c seems great. I don't know too much about a/c systems so could this be true? bHe said I only had about 12 ounces of freon when I came in to him, he tried to recover and recharge the system but said the pressure was too high. I think he said he added 4 more ounces before I left which made the car a/c worse so I took it back and he said he would put it back down to 12 ounces since I said the a/c was cooler than when he added the 4 ounces. Can someone please help elaborate on this a/c system thing and how it works?

duxthe1 · #2 06-24-2011, 09:47 PM

Too high of a high side pressure is not a compressor problem. Compressors fail by not making pressure, not by making too much. They also fail by leaking but that is irrelevant to your situation. Too high pressure is either a restriction in the high side, or an absence of airflow through the condensor. My diagnosis.... You need a new mechanic.

lsmalley · #3 06-25-2011, 02:48 AM

So what does it mean that the compressor pressure is too high on the high side and too low on the low side? how can I remedy it?

alamostation · #4 06-25-2011, 03:09 AM

Quote:

Originally Posted by lsmalley

So what does it mean that the compressor pressure is too high on the high side and too low on the low side? how can I remedy it?

I may be wrong, but to me the primary suspect is the expansion valve.

+1 on the new mechanic.

compu_85 · #5 06-25-2011, 09:32 AM

When the TX valve fails high side pressure will skyrocket.... like 400 PSI. While that is happening if you tap on the valve it will sometimes work correctly for a moment and pressures will normalise.

-J

lsmalley · #6 06-25-2011, 10:25 AM

The high side pressure was 350 and the low side pressure was 70.

duxthe1 · #7 06-25-2011, 01:31 PM

Those pressures sound like an overfilled system, ie too much refrigerant. The ratios aren't too out of whack, but they are both higher than they should be. A restriction in the high side would be pulling the low side a lot lower, but the low side is about double what it should be. My suggestion is to take it to somebody competent and have it recovered, evacuated and recharged with the proper amount of refrigerant.

lsmalley · #8 06-25-2011, 03:43 PM

I am at a new shop having my ac rechecked. I will keep you all posted on the outcome.

leathermang · #9 06-25-2011, 06:04 PM

Keep in mind that if you do not have the test conditions correct it can mess up diagnosing... to be safe one must have a good blower aimed at the condensor....the condensor fins and radiator fins straight and clean , high idle, windows open, ac on max, blower on low, thermometer in center vent...and things have to stabilize like 15 minutes to be accurate....

lsmalley · #10 06-25-2011, 06:20 PM

Thank you all for helping me address this issue. I took my car to firestone, and the issue was that the fan clutch (not the auxillary fans, but the main one) wasn't engaging. The guy showed it to me when he started the car he was able to stop the fan with his finger while the car was running. So as a quick fix to battle this 110 degree weather I decided to disconnect the aux fan temp switch so that they are always running at high speed which has rectified the problem of mediocre heat until I can put on a new fan clutch. Car now gets down to -10 degrees!

leathermang · #11 06-25-2011, 06:37 PM

-10 degrees !!!!
LOL, now we really can't allow stretching the truth that far... because people will start posting complaining their AC will only get to 34 degrees...
Which is the correct shutoff point so that moisture in the air does not freeze on the evaporator fins and stop cold air flow until it thaws... I had a car that did this and it is really frustrating out on the road.. hot, cold, hot , cold.... about 15 minute cycle times...

lsmalley · #12 06-26-2011, 04:05 AM

just did a retest of the temp, and got a steady toggle between -25 and -27 degrees while holding my thermometer there for 10 minutes 2 separate times. However, I did notice that it was on max cool and the ac never switches off, it runs continuously. I thought it was suppose to turn off once the desired temp was reached? Also, what part do I need to order since my main fan isn't spinning? Is it the clutch or something else? Part number needed please.

ps2cho · #13 06-26-2011, 04:14 AM

The fan clutch has nothing to do with your A/C pressures. Your A/C pressures are high because the aux fan is not keeping condensor temps down and now that you jumpered the fan, its keeping pressures lower.

Your pressure sensor might be toast. As mentioned earlier, sounds like your system is overfilled.

lsmalley · #14 06-26-2011, 04:24 AM

What is the pressure sensor and where is it? Also, the system is not over filled. It was just redone again today with whatever the amount calls for, 2 lbs I think. Are you positive the fan clutch has nothing to do with it? because, now my car doesn't run as hot anymore, but before it ran a little hot even with the ac off? And I know for a fact that the axillary fans did turn on once I turned the ac on.

ps2cho · #15 06-26-2011, 08:44 AM

Quote:

Originally Posted by lsmalley

What is the pressure sensor and where is it? Also, the system is not over filled. It was just redone again today with whatever the amount calls for, 2 lbs I think. Are you positive the fan clutch has nothing to do with it? because, now my car doesn't run as hot anymore, but before it ran a little hot even with the ac off? And I know for a fact that the axillary fans did turn on once I turned the ac on.

You didn't mention anything about a hot running engine...

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