300 E Ac Problem

I have 1990 300E/3.0. My AC was working fine. While driving in the morning, AC was on &cooling. In order to clear foggy windshield, by mistake I rotated the temp. dial to Max HEAT. Then, realizing my mistake, I pushed defrost button. After windshield cleared, I rotated the temp. dial to normal cold setting. The AC quit working. Blower is working, but I get only hot air.

Question: Could any body tell me sequence of troubleshooting this problem? Should I start with heater water valve? Is it also called monovalve? Is the valve located in front of battery?

Thanks

[J.HIDALGO]

However, since you were messing with the temp. dial, I would suspect the pushbottom controller first.

Just to let you know that I noticed the compressor clutch does not engage even if rotate the temp. dial to min. temp. Do you still think the push button controller should be checked first in troubleshooting? How do you check/pull the controller? Any link or threads that I can read?

[J.HIDALGO]

I would also check the ALL the fuses.