galileo55

A/C blowing air but not cold. I bought the gauges and measured the pressure. It's about 74PSI on both the Low and Hi ports. From what quick research I did, it's supposed to be about 40-55 PSI on the low port (depending on ambient temp) and about 250 PSI on the high port. The car was NOT running when I measured. Should it be running when measuring?

If measuring without car and a/c running is ok, I'm suspecting, from what limited knowledge I gathered on the topic, that the Expansion Valve is broken, making Low and Hi pressures the same.

Thinking about just replacing the expansion valve
http://www.ebay.com/itm/171672027699
and the Receiver Drier (it apparently has to be replaced whenever the system is opened)
http://www.ebay.com/itm/171780035107

Called Firestone and they will supposedly diagnose for $10, which I will do, possibly tomorrow, before ordering these parts.

If it's too expensive to fix, I might have Firestone just evacuate the R134A. I expect I would then: vacuum both Hi and Low ($20 pump that works off regular air compressor requiring 4.3CFM @90PSI. Might have to do it a few times since I have a small 8-Gallon compressor), adding refrigerant + oil, filling to the right pressure on low port and trying again.

I see there's also a "flushing" step. Not sure what that procedure is though. How is that done and when? I'm guessing before vacuuming.

Thank you

galileo55

So, it turns out measuring should be done with car and a/c running.
Once I did that, I found out both Low and Hi pressures are low.
Added 12 Oz can of refrigerant and got cold air. Low Pressure remained under 30 psi, high pressure was about 150 psi.
Added another 12 Oz can and pressure got higher but there was some clicking noise and I assume was from the compressor.
Added a third 12 Oz and pressure stabilized at 30 psi on low and just under 200 psi on high.
I was expected both pressures to get higher. They only got higher temporarily while adding refrigerant. I stopped there.
Car apparently calls for total of 30 Oz refrigerant so I now have about 6 Oz too many, minus whatever got lost in the low and high hoses to the gauges (hoping about 6 Oz :-). Car has ice cold air now. I'm leaving it like that and not letting some refrigerant out, in case there's a slow leak. Perhaps I'd have the right amount in a couple of months. If I knew it was going to to take the 36 Oz, I would have vacuumed if first.
Checked my 2 other Mercedes cars for comparison. They both run at the same pressures and have good cold air. I'm calling it good for now.

miatawnt2b

you did good. nice work. you probably have a pretty good leak in the system though. check your A/C hoses and the condenser for signs of oil.

Austex_Egger

Agree with Miat. You basically had no freon, must be a pretty significant leak somewhere. You an pick up a UV leak detection kit for pretty cheap. Probably be worth it to check it out.