heat/blower problems - 1998 4.0 ohv 4wd

[avid]

I'm having two problems with my heat/blower:

1. The blower only operates when I turn it on "high." From my research it seems this is likely to be the blower motor resistor and/or its accompanying connectors. Does this sound right? I am unable to do much with the truck now as it's single-digit temps outside at the moment, but would like to order the part so I can attack it if we get a warm day.

2. Yesterday, my heater quit blowing warm air. I had turned down the temperature selector switch from full-hot to medium-cold and then was unable to get hot air back after turning the temp back to full-hot. Is this likely to be the blend door and/or blend door actuator? I've read these can be problematic.

I replaced the heater core last fall, along with the entire cooling system, as part of replacing the engine. The AC is currently not functioning and is a project I hope to tackle in the Spring.

Appreciate the help. Like I said, it's too cold and snow covered outside right now to do much, but I'd like to get the parts so I'm ready when we get a warmer day.

 

[Craig0320]

Most likely blower motor relay. It is located on the blower motor housing next to the evaporator box in the engine compartment on the left side. Check to see if you have any cracked vacuum lines. There are a couple that plug in from the control unit underneath the blower motor on the passenger side foot well.

 

[avid]

Thanks. From what I've been able to find that seems to be the remedy for the blower only working on the high setting.

I'm familiar with those two vacuum lines as one of them was broken inside the engine compartment. I tried to fix it but I'll re-check it. When I replaced the heater core did I see it run into that connection plate (whatever it's called) in the passenger side firewall. It looked then as if the two vacuum lines on the engine side are permanently attached to that plate but I'm not sure about that. If they detach I could just replace the broken line when I replace the blower resistor. Do you know if they detach? And do you know if it's those that operate the blend door?

I should have replaced the blend door when I replaced the heater core. Should have at least checked it. But that was such a time-consuming PIA project I'd sorta forgotten I needed to check it by the time I got to it.

 

[avid]

Replaced the blower motor relay and the blend door and both issues are now fixed. The only blend door I could find is the Dorman replacement that asks you to cut up into the bottom of the heater box. Having only a couple inches of clearance there I didn't think I could do it so I disassembled the whole dash to get the heater box out, but then still cut through the box as I couldn't find a way to replace just the blend door in either the shop manual or Chilton book.

 

[Craig0320]

Yeah the boxes in our trucks suck for the most part. Glad you got it solved.

 

[avid]

Yeah the boxes in our trucks suck for the most part. Glad you got it solved.

Thanks. Solving those two issues were the bright spots of the several projects I am currently trying to tackle.

I'm also replacing the rear brake shoes and drums and I think some previous owner put the wrong size parking brake cable on the rear left side as hooking it up makes it impossible to assemble the system correctly (it was not hooked up when I opened it up for the first time and parking brake has never worked). Started noticing a little grinding noise coming from back there and when I opened it up to check the self-adjusting cable was broken and the parts were just rolling around in there.

Also replacing the AC system, which I seemed to have botched and for which I have another post.

Also replacing the factory radio. The CD player had never worked and I've gotten to enjoy playing music from my phone though bluetooth on my wife's car. Replacing it isn't too difficult but you know dealing with the little din kits is always interesting. For that I'm just waiting on the wire harness to get shipped.

 

[avid]

Here is a photo of how the blend door breaks. The old one is on the left, replacement one on the right (replacements are made of metal where it connects with the actuator to keep from breaking). The actuator operates the blend door by turning a post that fits into that 'D'-shaped opening. This photo was taken with the heater box removed from the truck (a multi-hour project as it requires removal of the entire dash, steering column, etc.,) and the actuator removed from the top of the heater box. Apparently, blend door failures like this are common. The symptom is that you lose the ability to switch from cold to warm air (and vice-versa) in your climate control system. In my case, the blend door got stuck in the cold air position.