'87 420SEL / 'not much heat' problem
 

I've read some posts regarding a lack of heat (interior heater) and see something called a mono valve or ACC mono valve. My '87 420SEL comes up to operating temperature but there isn't much heat going to the defroster or heater vents. The temperature is luke-warm at best...

Is the mono valve the most likely culprit?

Thank you,

Either the screen is clogged, or maybe the aux pump isn't pumping.

Pull the electrical connector off of the monovalve....this should give you full coolant flow...ie full heat. If nothing happens, unscrew the 4 screws, and pull the valve out - note the order in which the part go into the hole.

Thanks for the reply, Larry... does the electrical connector pull straight up to take it off? Didn't seem to want to pull off easily and I don't want to compound the problem by breaking it off...

I also see that I can purchase a complete assembly or for far less, just the mono valve repair kit, which based posts here, seems to be an easy repair. Do I need a complete assembly, and is it a lot harder to replace, since there are hoses involved?

Thank you,

Yes, straight up.