My 87 560 SEL has the following problems. Only has heat on defrost mode and only has high blower. No heat in all other modes but blower works normally. I tried a monovalve since I had a similar problem 5 years ago but that had no effect. Any ideas?

__________________
Tim Mabry
87 560 SEL
85 Chrysler Laser
72 IH
59 Rambler Rebel
57 DeSoto Sportsman
55 New Yorker
49 Dodge Turdmobile
47 DeSoto Suburban
40 Packard
39 Packard