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sprinkles08, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 22665
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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2003 MS320....A/C not working, suddenly stopped during

Customer Question

2003 MS320....A/C not working, suddenly stopped during operation with a small wif of burning smell. no visible smoke. went to recharge A/C but the low side was 125psi so wouldn't recharge. Replaced compressor, dryier and expansion valve. vacuumed system. but the low side is still at 125psi. not sure what to do next....
JA: How many miles are on the car? Have you been losing oil or coolant?
Customer: 55K.....not oil or coolant although the car was in storage for about 3yrs
JA: What is the model of your '03 Mercedes?
Customer: ML320
JA: Are you fixing your ML320 yourself? What have you tried so far?
Customer: I've tried
JA: Anything else you want the mechanic to know before I connect you?
Customer: not at the moment
Submitted: 10 months ago.
Category: Mercedes
Expert:  sprinkles08 replied 10 months ago.

Hello and welcome to JustAnswer!

If the system has been opened and vacuumed it isn't possible that the low side truly has 125 PSI. With the system opened it would have been ambient pressure, with a vacuum pump on a sealed system it would have gone into the high 20's in vacuum. You don't mention what you're using to charge with, but the low side gauge has to be incorrect.

Customer: replied 10 months ago.
thanks for your replay...OK, maybe I wasn't clear. yes I opened the system to replace the compressor, drier and valve but after securing all the fittings I connected A/C gauge system, with a vaccum connected to the low side pulled 28" Hg for a couple hours, closed the valve and turned the pump off to monitor if I had a leak. Verified after 2 hrs the I still had 28" of vacuum, no leaks. Turned the car on and the AC, connected a new can of Freon to the yellow gauge line (after I disconnected the vacuum pump). opened the low side valve on the gauge system, pierced the Freon can and witnessed the transfer of Freon for a couple seconds but watched the pressure indication on the low side climb to 125 and never deviate from that level. at that point I couldn't add anymore Freon....any help would be appreciated. thx
Expert:  sprinkles08 replied 10 months ago.

So it sounds like you've added refrigerant and the compressor will not engage?

Customer: replied 10 months ago.
my thoughts also, never saw a change in pressure where I expected it when the compressor would engage. any way I could manually engage the compressor to see if it would come on? I'm going to take it back out today and check the connector and verify I had a good connection.
Expert:  sprinkles08 replied 10 months ago.

Yes, you can apply power to the compressor to see if it will engage if the system is properly charged, just keep in mind there will be no protection against pressure or freeze up.