No heat

[Lmgrcivic]

the truck will not blow heat or ac untill Im driving about 60mph. but once I slow down its gone again. when Im on the highway it blows hot as h_ll.
I have blown out the coolant lines for the box and still nothing. dont know where else to go with it.

[bigcountrysg]

Check your water pump. I had the same situation. Ended up the water pump was not circulating water at idle. So when I stopped or sat idling I had no heat. But once I replaced the water pump I was back to normal.

[Lmgrcivic]

did you have any overheating problems or did you just replace it in order to figure it out

[bigcountrysg]

Originally Posted by Lmgrcivic

did you have any overheating problems or did you just replace it in order to figure it out

Nope same syptoms you are discribing. No heat unless driving down the road. Eventually I ended up having no heat at all. That is when I found out my waterpump was not circulating water.

My truck never over heated, but I had close to 150,000 miles on it. I figured I should change the water pump.

[Lmgrcivic]

finally got time to do the waterpump and still no heat

[lug]

Originally Posted by Lmgrcivic

the truck will not blow heat or ac untill Im driving about 60mph. but once I slow down its gone again. when Im on the highway it blows hot as h_ll.
I have blown out the coolant lines for the box and still nothing. dont know where else to go with it.

When you say blow I figure you are not talking about the blower fan and damper doors. It's the heat or ac part that seems odd. Have you checked the air intake area for debris? Do you get heat or ac while using the recirculate mode? Pine needles, leaves and dead bugs slowly choke the outside air inlet over the years.