Been looking at the factory manual and haven't found a test to show if the temp wheel is working correctly. The man. has a "box" to hook up for the various systems checks, but no common sense way to see if the temp wheel is the culprit. Most of the "tests" end with "replace PBCU with no way to whittle it down. My forays into vaccum pod replacement now has the air going to the right place when the correct PB is selected, but I have no temp regulation. All I get is max heat or no heat with no consistent PB selection to help narrow it down. I get no A/C compressor engagement at all, as well. I am going to check a few other things in the system, but what is the easiest way to check the Temp wheel? Is it in the man. and I just can't find it? Thanks Hot In DEN...... I might add that the blower works as well, auto and manual.

Anyone?

Various ways to test effect.

Actually, you do not need the temp wheel in any position for the A/C compressor to be on. All you need is to not be in the economy position.

The PBC will ground the signal from the Klima/MAS/BASE (depending on year/model) telling it to turn the compressor on in any PBC position except econ. The temp wheel does not decide whether to have the compressor on. That decision is totally based upon the PBCs evaluation of the evap temp sensor and possibly intervened with eng temp.

The temp wheel only is a variable sensor whose signal is compared to other sensor values in deciding how much to blend regulated heating and regulated refrigeration.

If you wish to see the regulation by temp switch, heating it would probably be easier to see as the control of the heater core temp is influenced by the temp setting on the wheel. If you look at the water control valve signal it should be 100% closed duty cycle at "Min", it should be 0% duty cycle at "Max", and the duty cycle should vary in between by the temp wheel setting and the temp of the day.

BTW, the easiest way to view the compressor on signal to the Klima/Mas/Base is at the low pressure switch on the drier. It passes through the normally closed pressure switch on the way to the compressor control section of the power relay Klima/Mas/Base.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician