Ideas about air conditioning problems - PeachParts Mercedes-Benz Forum

ksing44 · #1 06-07-2003, 06:59 AM

I am still a little afraid that I may have the dreaded and expensive air conditioning failure noted for these cars. Last year, in June, the air conditioning was recharged and filled with the fluorescent indicator dye. Then in the fall I thought the system was fading, but with the cooler weather coming I just thought I wouldn’t worry about it until the spring. Sure enough, it isn’t very cold this year. I thought it needed to be recharged a second time, so I was sure I was going to have to rip out the entire dash and pay the whopping $2500 bill for the fix. :wall: I was willing to pay, but I was concerned about getting the dash reinstalled. Then last week I took the car to the very good independent mechanic that did the recharging of the system and he told me that the pressure of the system was fine. He told me that he thought the refrigerant had not leaked out. He also tested the temperature from the vents and he told me the temperature seemed OK. It was a rather cold day, however, and the outside temperature was virtually the same as properly cooled air. On a hot day, the air conditioning does not get anywhere near as cold as it did before. Since the independent mechanic couldn’t identify the problem, I made an appointment with the dealer for the 19th of June and I am hoping they can solve the problem. Since the pressure is good, I am hoping it isn’t leaking from the evaporator located under the dash. Could it be that the independent mechanics messed up a bit and charged the system improperly? Could the pressure be OK and not have the proper amount of refrigerant? I read about being sure to dry the system before recharging and being sure to fill the system with the appropriate amount of refrigerant. I am hoping it is simple, but I am willing to pay what ever it takes to keep the car like new. I just hope the dealer can figure out the problem. If you guys have any tips about the possible problems, I would be grateful to hear about them.

cbdo · #2 06-07-2003, 07:42 AM

First, not to overlook the obvious, I'm assuming that in compressor-off mode it behaves appropriately. On monovalve cars like my '89, one cause for less-than-frigid AC is that the monovalve is sticking and the AC is cooling heated air rather than ambient-temp air.

Assuming that everything other than the compressor-evaporator area is OK, half the job was done earlier, but not the other half. Charging with the fluorescent leak tracer is good, but it's only informative if someone looks for the tracer a few weeks later--and from what you're saying, I assume there must be a leak. After all, if there's no leak, there's no need to recharge. Before doing anything else, I'd try to get the system recharged with tracer and then hunt around looking for the leak. If it's a slow leak, it may take a few weeks to show up.

ksing44 · #3 06-07-2003, 09:32 AM

Yes it is true that the air conditioning must have leaked the first time, but that occurred over an 8-year period of time, so I thought it was possible that the loss of pressure wasn’t really unusual. I was hoping that the very slow loss of charge didn’t necessarily mean that there was really and obvious leak that would need immediate repair. The mechanic did search for a leak, but never found it with his UV light and the dealer told me that sometimes it takes multiple loads of dye for the indicator to be visible in such places as the moisture drainage holes coming from the evaporator. Now that the mechanic is telling me that there was no loss of pressure, I am confused about the original loss of pressure and the lack of sufficient cooling. I will certainly ask about the "monovalve" and the possibility that the car is trying to cool heated air. The air does feel cool on a cool day, so it may be using ambient air and not be trying to cool heated air. Thank you for the help.

cbdo · #4 06-07-2003, 10:13 AM

Oh, well--it was a thought. If everything behaves appropriately when you're in no-compressor mode, the monovalve (and indeed the rest of the system aside from the refrigerant circuit) is unlikely to be the source of your problem. Good luck with it all, and keep us posted--I'm suspicious of a bit of problem with my own, but in my case there's reason to service the monovalve first and then see what's still left over.