Just recharged the AC on my 300SD. How do these #'s look? - PeachParts Mercedes-Benz Forum

otto huber · #1 03-30-2015, 06:26 PM

My AC has performed well the past 2 Summers, but it had become noticeably less cool recently, so I added a can of R12. The AC is now cooler than the other day, but not as good as a couple of years ago. I checked the PSI #'s after adding the can of R12 and came up with these:

Low side static 70 psi
Low side running 29 psi
Hi side Static 180 psi
Hi side running 190 psi

Also, when I went to put the pressure gauge on the low side valve, there was a very faint hissing. After removing the gauge gas was blowing out and I frantically put the cap back on and can no longer hear or smell anything coming out of that line. I guess that the valve is shot. Will that cap keep the system closed?

engatwork · #2 03-30-2015, 07:52 PM

Not really.

JimFreeh · #3 03-31-2015, 06:10 AM

Quote:

Originally Posted by otto huber

I guess that the valve is shot. Will that cap keep the system closed?

Might buy some time using Teflon tape on the threads.

Jim

JimFreeh · #4 03-31-2015, 06:11 AM

Quote:

Originally Posted by otto huber

I checked the PSI #'s after adding the can of R12 and came up with these:

Low side static 70 psi
Low side running 29 psi
Hi side Static 180 psi
Hi side running 190 psi

I would expect the hi and low side to equalize.
How long did you wait until you read the pressure readings?

Jim

funola · #5 03-31-2015, 08:59 AM

Get this tool
How To Replace Leaking AC Schrader Valve Cores That Leak Freon Refrigera...: https://youtu.be/DwKVsSZz5Nk

vstech · #6 03-31-2015, 09:44 AM

70 psi equates to around 70F ambient/cabin temp... 180 equates to around 130 ambient temp... so, the car must have recently been running and the condenser was hot when you took the static pressures...

the leaking core will most likely need to be replaced... I would strongly recommend you find one of the tools funola linked to, or call around to HVAC contractors and ask if they could change a core under pressure for you. the cap will not hold the pressure well.

running 29psi is ok, depending on RPM, and cabin temp. the running pressure of 190 shows condensing temp of 133.8 so depending on your liquid line temp, the system could be working, or it could be over or under charged, it could have a dirty condenser coil... hard to say. need a lot more numbers to determine function.

barry12345 · #7 03-31-2015, 10:41 AM

In my opinion you will still lose some freon when changing the valve with the tool. There is one model out there the manufacturer claims has no loss.

I want to try a modification of mine to keep the valve insertion shaft tighter. Anyway without the tool you will lose probably almost all the freon.

Wear good gloves and good eye protection for sure when doing this.

Alternativly you may be able to buy a brass cap with a good o ring or rubber insert in it. Not absolutly foolproof but will not allow leakage on the threads. Perhaps not the ideal solution but should work okay.

otto huber · #8 03-31-2015, 12:33 PM

Thanks for all of the replies fellas. That video doesn't give me enough confidence to try that repair at home, so knowing that there is such a tool on the market, I'll see if there is a shop that has one and can do the repair. In the meantime, I'll try to find a cap with a gasket to buy a little bit of time. Would spraying soapy water around the cap show a leak, or would I need a specific tool?

I took those numbers a day after I charged the car. The car had been sitting for a couple of hours before I read the numbers, so I'm not sure how hot it was.

franklyspeaking · #9 03-31-2015, 03:30 PM

If it is leaking soapy water will show the leak.