W123 Intermittent heater
 

My heater, when asked for heat, comes on and off with no apparent rhythm.

Any ideas?

Does your car have manual or automatic climate control?

Automatic

What year is your w123?

1985 California version

Unplug the monovalve on the firewall and see if you have full heat all the time. If you do, the CCU is probably the issue. If the heat is still intermittent, replace the monovalve cartridge. Don't waste money on aftermarket parts either, there's a high probability that they won't work.

Thank you.