Since yesterday my heat is only working when I have it on highest setting (4),
Recently it wouldn't work on 1 or 2 either.

Any ideas?

Thanks

 

Read the HVAC FAQs which you skipped right over in posting.

 

Blower Motor resister

 

I don't have time to find the link to that thread do you suppose you could post it for the new guy?

If the blower only works on high it's likely the thermal fuse on the blower motor resistor has blown, not terribly expensive to replace but it's a a good idea to check the heater core evaporator core for restrictions before you throw new parts at a problem.

 

You've been here how long and don't know how to read stickies that say READ FIRST or even to look in signatures?

 

This is what projectSHO89 was referring to https://www.ford-trucks.com/forums/7...xpedition.html , lots of good info there but I didn't find anything related to your problem on that thread.... Yet.

 

Well, dogggone it! I could have sworn that was included.. Sorry, guys!

Anyway, see post #3.

 

Post #3.

This is most likely your answer, speeds 1-3 run through resistors to reduce amperage to slow the blower motor down. 4 or high is direct full current to the fan and will work even with a complete resister pack failure.

 

I just discovered I have the same issue with the blower only 'blowing' on high. Lotsa air coming out the defrost though.
So I checked the 50 amp fuses, and they are fine as expected. Then I pulled the blower resistor, and it looks clean with good connections and no shorts or anything obvious. But, is there any way to test that tiny thermal fuse and avoid buying a whole new resistor if this isn't the source of my problem?

 

The thermal fuse can be tested with an ohmmeter (multimeter).

 

It tested out the same as the coils, so I presume I might as well just re-install the unit. Must be a problem with a valve or diverter somewhere. Was hoping for an easy fix


My van dash has a large 5 sided access panel on top and close to the windshield on the passenger side. I wonder if that is to get at some of the heating equipment. Would require prying it up, so haven't ventured into it yet.

 

I haven't had one out of a 06 yet but if it looks like this,
The thermal fuse is the small round thing with the blue stripe on the top of the picture. you should get a zero resistance reading and a jump up in ohms for every resistor coil from the fastest to the slowest speed.

If the resister pack tests out OK I would recommend investigating the switch in the dash next. And does it only blowout of the defrost or is that what you are using intentionally, (unrelated question)?

 

Yes, its similar to that, though the configuration and location of the resistors is a little different. No, I wasn't selecting the defrost intentionally, so the system has defaulted to that. Normally, one would expect that to be the resistor block as cause, but not in my case it appears. I really don't think its the switch either, but I'm not sure.

 

If your airflow has defaulted to defrost and cannot be properly selected, you actually have TWO separate faults with the HVAC:

Assuming that you do not have a "stripped chassis" van that your coach builder built the dash controls for, the inlet/outlet is controlled by vacuum, the blower speed is electrically operated.

 

Thanks, and isn't that just great:/ I'll do a more thorough diagnosis when I can give it a run again over the next few days.
The coach builder didn't mess with the HVAC, I'm pretty sure of that.




My troubles seemed (or coincidentally) happened after both chassis batteries were flattened for some strange reason. I had a parasitic battery drain after it sat for two weeks (starting with fresh batteries) after a trip - so, its possible there is/was a mild short somewhere in the system - they don't seem to be draining at the moment however. No fuses were blown.
I really should check the switch assembly to eliminate that....I presume I can pop the radio/CD out and I can pull the electrical harness off the back of the switch which I can reach that way.