Heat not working, 2006 vnl670

On older models of any truck, they use hvac controls that have mechanical controls compared to newer trucks that use electronic switches to turn heat and ac on and off.

On the engine (i have no idea where on your volvo) there are two valves. Sometimes they look like a regular garden hose valve. They open and close and allow hot coolant to run through the heater box which heats the air blowing into the cab. Both valves have to be open open to allow flow of the coolant. Ask your shop if you have them and where they are. Come summer time you want to close them to have optimal AC, winter you open them to have heat.

 

How is the coolant temp? If it isn't a valve preventing coolant from circulating to the heater core, your thermostat might be facked.

 

Ya that sounds about right. It won't be the thermostat then....

 

First of all, you people driving riveted boxes with picket fences for doors, like Centurys for example, may have to drop the idea that Volvos have shut-off valves for coolant. They generally don't. Of course in diagnosing this problem you first have to ask if the blower is working; and for that matter, are both blowers working, front and rear (as in sleeper)? The coolant to each heater core (and the refrigerant to each evaporator, for that matter) generally move independently, so if the front blower doesn't blow hot air, the rear at least should, and vice-versa. The guy who said (possibly in this or another thread) that you have to check your coolant is basically off, because if you were so low on coolant, your engine would be burning up and you'd be solving that problem instead of your heater problem.

Recently I had a 2012 Volvo 670 that didn't blow heat from either blower. That was perplexing, as it made me brainstorm for a single problem that would affect both blowers. First I checked to see that the coolant hoses were hot near both heater cores (you can follow the heater hoses from under the engine air filter by the firewall). Both sets of hoses were hot, yet neither blower was blowing hot air. Since it's far easier to get eyes on the sleeper blower than the dash blower, I raised the mattress and discovered two wires unplugged from the top of the blower area. Those wires control the heat blend according to the dial on the sleeper wall. Plugging those two wires in solved the problem of the rear blower blowing only cold air. They probably got pulled out by jostling some mudflaps around in the storage compartment. Still no heat at the front -- that may be some kind of heater-control valve; will try to remember to post the outcome when I solve that problem.