I'm trying to track down a problem I'm having with my truck and I can't seem to find anything online.

On my 02 7.3 4wd excursion the front hvac doesn't seem to do anything when the temps are near or below freezing. But once the truck gets near operating temps everything works as advertised. Can anyone point me in the right direction?

 

What do you mean "nothing works"? It doesn't move any air? It does move air but not warm air?

 

The hvac doesn't move air

 

Can you hear the blower motor running?

 

I do hear the blower run

 

If the blower is running, then you need to find out where the air is actually going.

 

I assume one of the doors is not opening. There are some vacuum actuators in there and if they aren't getting enough vacuum until the engine gets to operating temp that would be the issue. Is it a problem with a leak? Vacuum pump? or one of the actuators I don't know. This is the only thing I can think of.

 

A cold engine won't have hot air to move until motor warms up.

A few more details on the issue would be helpful.

Does air blow out vents when vent is selected?
Do you feel air along with hearing fan motor?
Does air blow out defrost when that mode is selected etc.

Do you have esof, 4x4 auto hubs? If so are they working ok?
Does air switch from vent or floor to defrost when selector is not in defrost mode?

Have you put a non oem or non international thermostat in it?

 

No, but it will still move ambient air.

 

Have you seen a reference or know of a way to go about diagnosing the different actuators under the dash?

 

I understand that on a cold morning I am only blowing ambient air until the engine warms up. I do have ESOF and the hubs did work until I replaced them with Warn units. I do have an aftermarket 203 degree t-stat but again the temp isn't the problem. My vacuum pump works and I hear it run every time I turn the key. I don't know if that is indicative of something. Should the truck hold vacuum when off?