Air Conditioner Problem

I have a 1990 190E 2.6 and I'm having a problem with the air conditioner not blowing cold air. It works fine at the lowest setting, but when I push the low setting to the third and fourth (Hi) positions it blows hot air. If the sun is directly on the car and the outside temperature is more than 84 degrees the air conditioner will not cool the car off. I end up putting my windows down and opening the sun roof to get some relief. It seems to cool fine if it is cloudy, night or less than 80 degrees. Even when the air is on low and I feel cold air coming from the vent I can hear a hissing sound. Any ideas? Thanks.

[Mike Richards]

Have a tech connect manifold gauges. Low side & High side readings will tell the story. It's sort of like compression testing an engine.

Your problem may simply be low refrigerant, but that really cannot be determined until the system has been professionally anaylzed.

Such an analysis shouldn't cost a great deal.

Mike,

Thanks for the info. Should I look around for a Mercedes mechanic or will any local guy do?

[Mike Richards]

I'd hire an experienced MB tech. Many MBs are plagued with all sorts of air blend problems - servos, etc. within the dash that blend outside air with cooled air. Sometimes you may have more outside air entering the system than what's been requested. A "generic" tech isn't going to know the ins & outs of the MB system.

My 2 cents.

I had the exact same problem with my '91' 300E, problem was a bad expansion valve. Replaced the expansion valve, cools real nice now.

Mike,

Thanks for your 2 cents.

brcrosson,

Is it a tough do it yourself job to replace the expansion valve?

JeffK
Had a indy shop specializing in german car A/C perform the repair, would not have know what the problem was, and I have a warranty on the repair.

brcrosson,

Thanks for the info.