Ru rammin 2?

I have a 1994 3/4 ton ctd standard cab 4x4 5 speed and the heater/ac sometimes quits blowing air. the fan still runs on each setting and you can switch the dial to different settings but none of it reclaims the circulation. it sometimes does this for two or three minutes and has previousley lasted all day. it moves some air, about a little less than it would on the lowest fan setting when the system is working properly. I have taken the whole system out of the truck and replaced the heater core and blower motor but other than the heater core being a little bit restriced and the blower having a bad bearing I have found nothing wrong. My dad has the same problem with his 1995 ctd but less often. Is there an easy fix to this or are we fortunate enough to have two dysfunctional trucks?

dieselman2300

Sounds like you have the broken blend door problem. Our trucks have whats called a blend door. They have a tendency to break and then they just do what they want. Unfortunatley, you have to take the whole dash apart to fix it.
Do a search for blend door and you will learn alot.

Ru rammin 2?

thanks but the doors all seem to be fine. I didn't see any problems with the blend door or the actuator cable. Ill try the search though. wheres the best place to search for it?

Busboy

You say the fan motor is running..........but is it running at full speed? Check for 12 volts at the motor. I think that is your problem, look at the ground for the fan, if it's at all lose that will cause it. Failing that take out the resistor block and see if the coils are touching each other, they should not be touching. Some resistor coils are stuck together with an epoxy insulator to stop them from moving around, if it has broken the coils can touch each other. These things are easy to do, if both of these are ok then pull the fan sw and have a look at the connector, if is discolored at all thats your problem.

Ru rammin 2?

the fan runs and you can hear the change in pitch when the switch is moved. I will look at the resistor but the ground looked fine and the plug on the switch looked fine. I think that the fan runs fine since I can hear it but I might replace the resistor anyway. are they prone to go bad?

Busboy

The resistor blocks very rarely give trouble but if the truck has been in an accident or driven hard off road then the coils could have been bent. If you can hear a change in pitch then I suspect they are ok. I would check for 12v at the fan with sw on high, if as you say you did have a motor with a bad bearing chances are that the amp draw was high and could have partially melted any of the connections from the sw to the motor. Like I said ANY discoloration is a sign that it's been over heated and the melted plastic film provides a resistance. This is a common problem. It doesn't usually come and go that's why I'm suggesting a grounding problem, that would make it come and go.

I have seen occasions where the squirrel cage in the motor has stripped the "D" and the motor will still turn the cage but not always at full speed, you should hear one hell of a noise though.

Busboy

If you can get it to quit then disconnect the motor and run 12v to it, if it's ok that would point to either a fan sw or a connector partially melted, or the resistor block.

Ru rammin 2?

I pulled the resistor block and looked at all of the connections. I was an electrician for a while and all of the connections looked fine to me I have to replace the switch anyway and also the fan motor so I might be subconscously fixing the problem anyway but I have a feeling that I haven't yet found the problem.

Busboy

It's unlikely the new motor is bad but stranger things have happened as they are assembled by the lowest bidder. By putting 12v directly to the motor will tell the tale. Good luck. Just a thought, are your battery cables tight and not corroded?

Ru rammin 2?

the battery cables are new but i am currently waiting on parts so I haven't had a chance to test it yet but as soon as I get all of my parts I will try the 12 v thing on both motors and see if I detect a difference. I'm open to anything at this point. hundreds of dollars in parts and an excruciating disassembly of the entire inside of the truck I want it to go back together knowing that it is going to work.