Another A/C question...

Hi everyone!

I did the search but didn't come up with anything remotely answering this question. I have a 1993 190E with 2.3 engine and it was in the shop a week ago for engine replacement. They also did A/C maintenance (I know the shop very well and trust them completely) - pulled vacuum, recharged it and put some oil in. Prior to maintenance the A/C would only blow cold air at speed and not-so-cool at idle, which lead everyone to think that it was undercharged. Now, the compressor engages (just as it did) no cool air comes out at all. Ambien air is all I get - at idle or speed. The shop did the measurements and they said the system holds the pressure fine and builds up pressure difference. They said it might be dirt in the system thats causing it. Now, the charging port thats on the front of the car (near the fans) is getting awfully hot, the other port (near the fender wall) is ambient. The sightglass is clear and I can see streams in there. What should I look at next?

[RSH]

With the addition of the oil, It may just be overcharged, that will adversely effect how it cools, do you no what the pressure readings were? If you trust them as you say you do, make them fix it, since it did work somewhat better before they touched it.

Thanks for the response. Something else I noticed today while driving. I was at highway speed (65) and I noticed that center vents were letting a bit of warm air through (warmer than ambient) so I shut the center vents off and switched the A/C to see what would happen. Sure enough, the left (drivers) vent started blowing cold air. Opening center vents again only provided warm air and the cold air in the left duct became warm too. What am I looking at here?

Thanks!

[RSH]

Well, now that you do have some cold air, the vents are controlled by vacuum, did the vents work correctly before the engine replacement? If so, I would first start looking in the engine compartment for correct vacuum connections and leaks especially around the firewall, and if yours is an automatic check the vacuum line going to the modulator, if no problem is found in the engine compartment, then check the vacuum connections behind the glove box which is fairly easy or last but not least check the potentiometer but the dash has to come apart for that.

[stevebfl]

The 190 has a vacuum operated heater valve. It is loacted under the cowl. Good chance the vacuum is not getting to it. If you look closely with a flashlight the arm for the valve can be seen through the air duct at the base of the windshield (I did it somehow).

There also is a mixing door that is vacuum controlled and should be shut in A/C. It will keep the compressor of in the snowflake position if the door doesn't close. Use the top button for max A/C, the one that looks like a defrost icon. This confuses most people (including myself, for years). The point to the icon is that in a defrost condition one wants hot dehumidified air. They have a separate def button that lines this all up so I couldn't tell you why they used that icon there, but it is the MAX A/C position.

Without proper vacuum the recirc door will stay open which kills A/C on the 190 especially.

The low side line should be cold not ambient, no matter what all those doors are doing. Pressures tell the story here.