I have had this truck since oct 09.
When I got it the AC would not cycle (no activity at the compressor).
Whey the winter began I could get some heat from the heater but as winter has worn on the heat has reduced to cabin temps (no heat).
I can turn the heater off and wait a few minutes then cut it on and feel some heat but will quickly go away.
I have not removed the hoses going to the firewall yet to see if I have water flow. I thought I would ask here first and maybe save myself from making a mess with anti freeze.
I am wondering if the hot cold dial may be out.
Has anyone experienced this? what were your symptoms and fix?

 

Check to make sure your coolant level is not low. Do you hear the duct valves changing when you change the controls---could be a vacuum line problem. (i could be wrong about that ...not sure what year they did away with vacuum.) Another possibility thermostat stuck open...does the engine temp gauge show normal after warmup?
A/C clutch not engaging can be caused by low freon or electrical problem. Check fuses for a start. If freon is low, look for leaks (oil) at compressor seal, hoses, condenser, etc. You can turn the compressor clutch by hand (engine off) and make sure the compressor isn't froze.

 

the temp dial is mechanical-and the vent system is operated by vacuum. I would bet the heater core is plugged. As for the ac-I honestly wouldn't even bother with it now-you need heat

 

Thanks for the responses.
and here are the responses to the questions raised.
Yes the water temp gauge on the cluster moves to dead center and stays there as the engine warms up.
This makes me think that the thermostat is working properly.
question: What is the diagnosis procedures and symptoms to check for stuck thermostat?

Yes the duct doors are all actuating by the vacuum. And, appear to be working fine.

The temp dial swings very freely left and right with no resistance. That is making me think it is just a sensor with no real cable going to it. If there should be some resistance here then the problem may be here as this gate would be stuck in one position.
Question: should there be resistance on the cool air/hot air dial? Or do they operate with very little force to rotate the dial?

The air conditioner will be needed as soon as the month of may since this diesel is so loud I wouldn't want to drive with the windows down. So I'd like to get a start on this problem soon.
If the fix is the temp dial then this will also more than likely fix the air conditioner. So I threw this symptom in as a possible related symptom.

The plugged heater core is sounding like something to check too since I repaired a 17 inch crack on the water jacket.
Metal shavings could have clogged the core.
I don't guess any kind of radiator flush would help if this is the problem. Sounds like the heater core will need to come out and be checked/replaced if indeed this is the problem. Messy job. But driving with warm fingers and toes would be worth it.

 

yes the heater dial should have a bit of resistance to it-perhaps the cable is off. Also, check that the *** is pushed in all the way-if not the *** will not move the cable-the diffrence between the *** "in or out" is only about a 1/16 to 1/8 " so you may have pulled it out without realizing it.

 

The temp (also known as "blend") is not mechanical, it is electrically operated. There is a small electric motor on the bottom of the heater case that moves the blend door back and forth. This will need to be checked for operation. The motor itself may have failed(though this is rare)....there is a small plastic coupler between the motor shaft and the blend door shaft, this piece commonly breaks. To check, turn the igition key on, and move the temp control back and forth from cold to hot and back........you should hear the motor running, and the blend door hitting the stops on either extreme. If the motor is bad, you'll get no movement/noise. If the coupler is broken, you'll hear the motor running, but the door will not move. The motor and/or coupler can be changed without removing the heater case, but it will take some effort.
With all that said, I'd also check/flush the heater core as said above, definitely a good idea anyway.

 

blend door for a 98.5 is cable operated..Unless, like the fuel tank module, they used more then 1 type that year

 

With what you said about the block repair was the heat working ok before the repair ???

If yes then i would remove the heater core feed hoses and then reverse flush the core with water and air pressure then see what you have for flow.
This would be a good start either way smart, simple and cheap you got to have hot water flow before anything else comes into play to get heat.

 

Biododge1 I think you hit the nail on the head.
I moved the dial and could feel the electronic lever moving. I was pressing my finger on the motor shaft to see if it worked while I operated the lever. At one point I got good hot air then after I removed the pressure it slowly went cool again. I'll take it off and see what I can see. update after.
Thanks

 

Thread is old but that was the fix for sure.