Merkey,
Steve Brotherton's treatise on A.C. below,(an excerpt first):
"The biggest challenge in the diagnostic process is the extreme intermittent nature of failures in this system. The system consists of two controllers: The pushbutton controller (PBC), located in the console; and the compressor control relay under the hood (called Base Module, Klima or MAS, depending on the model and year -see photos).
These two controllers have very different mission statements. The pushbutton controller is concerned with temperature control as it relates to occupant comfort. It controls the compressor clutch for evaporator temperature and humidity during defrost conditions. It also sends a control signal to the compressor control relay whose mission is to control the compressor to meet the engine's needs.
The compressor control relay monitors the engine speed vs. compressor speed to protect the belt system from a locked compressor. It disengages to protect an overheating engine and to provide extra power in diesel models, and may possibly disengage to protect a low or erratic idling motor or an under-voltage system.
The first place to start in this diagnosis is to decide which controller is disengaging during the event. The easy access is at the low/high pressure switch on the drier. The signal from the pushbutton controller passes through the switch to the compressor control relay. This is a ground signal in most, but not all, cases. Verify the signal when the system works, then monitor the signal to determine which controller drops out.
Pushbutton control problems usually are just that. In early units, the controllers had internal connection problems, bad solder joints and poor connections between the temperature wheel and switches to the PC board. Occasionally, there are evaporator sensor problems and control often goes astray when the aspirator pump won?t pull air over the ambient air temperature sensor due to pump or tubing problems.
The inside controls have self-diagnostics on later versions starting in 1990. These diagnostics can be read with an impulse counter or LED on models up to 1994. The code is read by initiating self-diagnostics, which is done by grounding the appropriate system pin on the diagnostic socket for two-four seconds. The code can be read by monitoring the pin with an LED powered by the battery.
The diagnostic pin will be grounded for a number of flashes to transmit the code (Code 4 = four flashes, etc.). After reading all codes, they can be erased by rereading and then grounding of the diagnostic pin for six to eight seconds. Each code is to be read and erased until Code 1 is reached. Code 1 indicates no faults. This method of self-diagnostics can be read on any system (with self-diagnostics) up to when the systems went digital beginning in 1995, depending on the system."
http://www.peachparts.com/Wikka/AcDiags
Jeremy's Q.and A. with B.C.:
http://www.peachparts.com/shopforum/diesel-discussion/172032-klima-basics-missing-forum.html#post1344819
Briars and MB doc "Tow the Line" about Klima testing:
http://www.peachparts.com/shopforum/tech-help/102024-klima-ice-cube-not-working.html#post696584
Finally the Whole A.C. Wiki DIY P.P. Catalog:
Climate Control:
J.F.s "Page":
http://pages.prodigy.net/jforgione/MB_X11.htm
Arthur Dalton's instructions on how to assemble an inexpensive test light
probe from Radio Shack components.(Ala Mr Schwartz and Kestas):
E320 16 PIN DTC Charts inc. pin 8, pin 14
[My Ancient Dell has the ability to access the almost totally unused resource
"Advanced, Search" function of this forum.'Lucky Me!]