I had one mechanic doing a tune up and he said he wasn't going to blow through heater hose....Said it was bypassed for a reason...Anyways...He blew from the right hose to the left.

Took to another mechanic and he got heat to work.

He said you need to blow right to left.....and also the left hose to right?

---I bought the truck and the heater core was bypassed so maybe entire time heat worked I really don't know...But thought I would mention blow both ways.