A/c doesn't work, Tach intermitant
 

I am having a proplem with a 87 300D turbo. Tachometer only works when engine is cold. then tach quits when the engine warms up and so does A/C. I have replaced the Climate Control unit. That fixed some other problems with A/C-Heat control, but not that problem. A/C works fine when Tach works, but no A/C when the tach is inop.

I can rev the car up 3000+ and the tach will start working when engine hot

Anybody out there know what controls the tach. Is it possibly return signal in the Intrument cluster. Any help would be greatly appreciated.

I don't know exactly what it is, but if it were me, I would guess that a fuse, or some other electrical connection has either a hairline crack or is dirty or ??, and that once it gets warm enough, thermal expansion gives sufficient contact. So, I would be checking fuses and electrical connections with a fine toothed comb.

Try the overvoltage protection relay or klima relay. They are behind the battery if you remove the plastic shroud in the firewall region.

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I have changed the overvoltage relay. What is the klima relay, and where is it at.

It is next to the ovp relay.