Heater Problems

Hello all. The heater works fine in the back of the tractor but there is "NO" heat coming out of the vents in the front. Only cool air blows out of the vents so it tells me that the vents are connected. Any ideas of what I should look at or do to fix this problem? As always, thank you very much and sorry if this is the wrong forum.

 

There should be a filter in your cab heater. Where it is will depend on your truck. Chances are it has never been replaced since the truck was new. These will plug up and block the air flow.

 

could be one of the doors inside of the heater box is not operating. you need to check for vacuum lines that may have fallen off, or even a control cable to the heater box that may be loose or fell of its mounting. some a'c-heater systems have a vacuum module mounted in front of the heater box, that may be stuck in the closed position. this looks like a round small can.

 

There is a valve that adjusts the temp coming out. Depending on your truck make/model is where it will be. My company has a lot of International trucks & this is a problem on most of them.The valve on these is under the passenger seat.

 

Thank you for your responses. It's a 2002 Freightliner. Where will this valve be?

 

What kind of FL? Classic?

 

Oops...it is a Century.

 

Sorry don't know anything about them so I'll just guess.

If there is an access panel under the dash between the seats, take it off and the valve should be on the right side. You should see water lines going to it.

When you do find the valve, feel the lines before and after. The lines should be hot before the valve and not after if thats the problem.

 

Find your heater hoses coming off the firewall under the hood. Follow the hoses to the engine and there should be water shut off valves at the engine side where they are connected to the engine. Make sure the valves are open. Some people close them in the summer so the AC will get colder.

 

they guy says he gets heat out of the rear heater....not from the front vents.....if the valve under the hood (which i thought about before i answered) was closed, wouldn't that stop ALL flow of circulating coolant...????

i think it should......

it might be a control vacuum switch problem (the panel slide controls for instance), a vacuum line off, a vacuum "motor" gone bad.......i think its in the heater box assembly also known as a plenum.