I have a 2004 1500 I bought brand new. I has 240K and pretty badly rusted out but has so far survived the Wisconsin winters and the nasty salt solution they spray all over the roads.

The problem I am having is the heater fluctuates between cold and warm, almost like it's cycling on and off. The blower is blower and the air comes out of every position. This problem seems to mostly happen when the truck is first driven 25-30 miles in the morning and then all is well. At night, after work, the heater seems to work properly. I've searched this forum and have found a few posts with similar but not exactly the same problem. The posts I've found seem to have a problem with cold air coming out one side and warm air coming out the other side. As far as I can tell this is happening across the truck although I have never thought of checking until after reading some of the posts. I had problems with the fan blowing a while back. It would only blow on high or not at all. I replaced the under dash heater and that seemed to fix it for a while, now the fan blows on low, lower on medium and full when set to high. I can live with that but the cold/warm cycling is bothering me, especially when I need the defroster.

 

Low on coolant?

 

Could be but the temp gauge is in the middle of the range. I can't get my hood open to check. It's been so cold around here and I don't have a warm place right now to pull it in and crawl under it to try to disassemble the latching assembly. This truck has been a really good truck but it's on it's last leg, hoping I can get it through winter.

I hope to be able to pull it in my shop today or tomorrow to get at it.