hey guys i got a problem on my 03 boss f150 my heater works fine when im driving but everytime that i slow down it starts to blow out cool air. then when i start moving again it starts to blow real hot like it should, now it does this everytime that i slow down and speed up... any ideas???

 

Check your coolant level and make sure it isn't low.

 

Do a search...

https://www.f150online.com/forums/sh...d.php?t=312447

I think it could be something with the vacuum system... does it get cold when you apply the brakes?

 

His symptoms are classic, 'low coolant'.

Plenty hot with the tach up.
Loss of heat tach low.

 

A '03 with low coolant... could be plausible. Figuring it's about 5 years old. I'd suggest a coolant flush maybe in the spring.