Truck AC/Heat

[pilotjcd]

Heat accuator for a freightliner 120C. How does it work (vacume/electric)?
How is the best way to access the accuator to troubleshoot? The heat is on full blast in any temp setting.

[jiptwoo]

I may be wrong but I believe the vacuum part controls the position of the damper, ie. heat or cooling. The electrical controls fan speeds, and it sounds like a bad thermostat to me. Don't be mad if I'm wrong, good luck. Don't forget to shut your heat valves off at the engine.

[bob h]

Heat accuator for a freightliner 120C. How does it work (vacume/electric)?
How is the best way to access the accuator to troubleshoot? The heat is on full blast in any temp setting.

the hot/cold valve used to be powered by compressed air. if memory serves at all; it's found behind the dash panel, beneath the glove box, near the floor, on the passenger side

diesel engines don't make vacuum... you need throttle plates (or a pump) to create a vacuum

[uncleal13]

In 98 and 99 they were air operated. Not sure what year they changed, but I now have an 06 and the controls are all electrically operated using servo motors.

[uncleal13]

On the 98/99 models the heat valve was located on the firewall under the hood. Follow the water lines going into the cab from the engine compartment. Look above the air filter housing, you'll see the valve right on the firewall, you might have to stand on top of the passenger side tire to view it better. The piano wire cable may have broke either there or inside the truck right behind the control panel.

[carolinatrucker]

Heat accuator for a freightliner 120C. How does it work (vacume/electric)?
How is the best way to access the accuator to troubleshoot? The heat is on full blast in any temp setting.

Could the problem be the knob control on your dash where your heater/ ac controls are? Mine was stripped out and I got behind it and rigged it to stay on cool for this summer. I'll eventually have to purchase a new knob.