1987 420 sel NO HEAT
 

I hve no heat in my car at idle (maybe very little at idle just enough to feel luke warm) or driving.. I have read about a Mono Valve but my car does not have one heater hoses run from engine straight to heater core.. Replaced T-Stat no change... Auto unit on dash does have a mind of its own at times but when it seams to be working there is still no heat.. Once and a while I will get a relay around the glove box that will just sit and click on and off for five min and than never do it for another week or more.. Has a new blower motor mine was fried.. Grab heater hoses and they are hot top and bottom but still no heat inside car.. Temp guage on dash runs half way... A/C compressor has no belt but I still have no heat before the belt broke.. PLEASE HELP>>>

Along with the missing mono-valve, are you missing the aux. pump also? If so, it would explain your lack of heat at idle.