No Heat Control

Trace both heater hoses. Make sure you don’t have the valve inline. Next is to contact the dealer and get a parts diagram of the heating system. That will show you where the valve goes, if you have one.

 

It controlled by electric selinoid valve should be right near bunk heater same w cab look at bunk first easier to get. Should have a heater control valve . I’m sure you have the shutoffvalves turned on total 4 . Otherwise that’s how it works cable or electric heater control valve somewhere in lines If they were hooked straight it would be hot always check shutoff valves under hood first

 

I had a 92 Star Cab heater valve was on firewall( under hood) passenger side. Valve was air over electric type. It has an electrical and a 1/4” air line connection.Same thing under bunk. I think they were used up until 2000. If Valve goes bad it sometimes puts 100 psi into coolant causing many a head gasket or overhaul misdiagnosis.Very elusive as it only puts air into coolant once thermostat is satisfied and valve closes.