420 sel heater problem
 

The heater only putsout some heat on low speed,but cold air if I change to high speed or automatic.Also when i turn heater off,rpm jumps to 1200??
I also think,I have vacuum problems,for example power door lock not functionnning,fuel problem that could be connected to vacum.How do I check the complete vacum system for leaks,before I check individual units?

Low heat could be plugged monovalve, use Search for a lot of threads on monovalve repair.

While searching, look for Mity Vac, a vacuum gauge and pump, indispensible for vacuum troubleshooting work.

Best Regards,
Jim

Heater problem about to be fixed
 

For all of you having similar problems,I did a search on monovalve and found a post by Billybob.That post as complete directions and picture and really helpful.Thanks to that post,I will be repairing my monovalve this week-end,which doesn't seem hard at all,and should have my lack of heat taking care off. :sun_smile