I am having this issue where the heater is working fine then all the sudden it stops blowing warm air and turns cold. Happens a lot when I am up in the Mtns (Mammoth). I have not been able to pin point the main variables that cause it though, be it speed, altitude, or etc...

Any ideas?

Thanks

 

faulty heating core valve, or faulty engine temperature sensor

 

Are those expensive repairs?

 

since it's not possible to pinpoint the issue, it doesn't sound DIY to me, therefore going to the dealership to diagnose the issue is smarter in this situation. They will call you before proceeding with the part replacement after diagnosing the problem. Let them diagnose it for you, if they confirm that it's either an engine temp sensor or a heater core valve issue, then you should try to get the service manuals from renntech website, and then decide whether you can do it on your own or not. Otherwise, I believe it'd be around $400-500 level.