I have a 92 S320 that will not give me any heat whatsoever. Blower works great and even delivers air where I want it but will not get warm. The A/C works great.
I have a 5 hose duo valve but not sure how to test it to see if it is working. I have found a lot of info about the mono valves.
How can I test the duo valve to determine that that's the problem before I spend $200 on a used one or $450 on a new one?

__________________
1987 350SDL Parts Car
1987 350SDL #2 Sons Car
1991 350SD My Car-RIP 9/7/09
1992 300SD Her Car
1995 E300 Spare Car-RIP 4/23/09
1992 S320 My Car - Soon to be diesel
1990 W250 4x4 Cummins #1 Son's Truck
1993 D350 Cummins My Truck
1999 3500 Cummins Just Another Truck
1987 Executive Cat 3208 Family Wagon

"Growing up is a choice. Growing old is a privilege"