7 - Refrigerant Pressure in Bar - 04.3
8 - Blower control voltage - 21.0
9 - Software status of a/c Pushbutton control module - 02
22 - Terminal 58d (Bat Volt) - 0.00


Ed,

My 94 C220 should be exactly the same as yours. Your readings look normal while enginer off. 22 represents AC compressor RPM and it is, of course, 00 when engine is off.

Start your enginer then check 22 again to see if it goes up with the engine rpm. If so, the compressor does kick in. If not, the compressor clutch might be out or the PCU controller shut the clutch down due to some error codes there.

To read the PBU's error codes follow the procedure,
Key on with enginer off
Set temperature to LO
Press REST and "Defrost" buttons at a time for over 2 seconds (must be done in 20 seconds from last step"
If you see the LED on recirc button is flashing at 1Hz freq and screen shows "diR" you are in error code retrieving mode.
Press AUTO to read a contineous error codes at a time
Continue press AUTO and write all codes in your note until screen shows End

Now press AUTO again to read the intermittent codes.
Same procedure as contineous code reading above until screen shows End.

Make sure you log all the codes in your note. Let's see what you get.

Now the procedure to clear these codes,

Press '^' and 'V' at a time the screens shows "---". Codes being cleared.

The last step is somewhat different from what I experienced in my car. Manual says press ^ and V again to exit but I never success. So I simply turn key off, then start engine again. Turn AC on to see if you get cool air back. You can also check 22 to see if the compressor is running.

Hope it helps.

Charles from Taiwan