My 80 300d is blowing cold air on both the heat and defrost settings. any ideas?

My 1980 300d is blowing cold air on both the defrost and heat settings. Any ideas where to start? the engine temp looks like its right above 90 at running temp. thanks. victoria

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Body and Interior Specific Aid

Chassis Model Number

W123

Probably the valve that lets

Probably the valve that lets hot coolant in.

Unless you have a European model your 300D has the dreaded, expensive and very complicated climate control servo. It is that large black plastic unit on the right front side of the engine that has all the vacuum hoses and wires going to it. Your problems could be caused by a seized servo, wiring problem, loss of vacuum, failed amplifier, bad dash switch panel. This is a very tough system to troubleshoot and not easy for a beginner mechanic. A rebuilt servo and amplifier costs around $600. I am currently testing a new electronic replacment unit on my 1980 300SD that I am quite impressed with but it costs around $700. We have a manual control over-ride repair kit for under $100. It will give you hot and cold but will no longer be automatic. I recommend you find someone who knows this system who can help you troubleshoot and repair it.

thanks Kent. you're the

thanks Kent. you're the best. victoria