I am troubleshooting a climate control problem in my 88 300E.

I get one flash at the diagnostic connector pin 7 which is supposed to indicate all systems are go in the climate control system. Is this a reliable check of all temp sensors, or do I need to go to the CCU connector with an ohmmeter to be sure?

Everything else I've checked points toward the CCU as being my problem as long as a temp sensor is not bad.

Thanks for your help.