Volvo 770, no sleeper heat

There should be a valve on the coolant lines in the engine bay, usually above the passenger steer tire splash guard, that opens up and allows the coolant to flow to the sleeper heater core. Check to make sure that the heater hoses are all secure and none of them are bypassed. Check under the truck at the sleeper HVAC to make sure those lines are connected and not pinched off. I don't think there's a blend door to control the temperature, I'm pretty sure that valve is what is used to control it. I might be wrong, though, the 770 is an older model that I'm not very familiar with.

 

I'm not sure if this will help since it's designed to show you where leaks are, but it might give you an idea of where to look for your issue. Around 1:00 it shows the area where I would start looking for a valve. It should have some sort of actuator like a cable or electrical connection to open and close it. The valve I talked about earlier was the bypass valve and probably isn't the problem, it should be fine if you're getting coolant to the sleeper heater core. Even if you find the part, I don't know enough about the system to tell you how to test the part to see if it's faulty.

Mine had a leak and I bypassed it instead of fixing it, and I've never needed it. My bunk heater works for when I'm parked and the dash heater works enough to heat the whole cab while running.