tswcoaltrain

Please tell me I dont have to pull the dash out again!!!!!!!! I just got around to pulling the dash out because my evap core was leaking, so I did it right and replaced the heater core as well while I was in there. Well, the AC works great but now my heater just blows cold air. I was careful to make sure everything fit back together right and checked to make sure the doors moved before I put the box back in the truck. plugged the two wiring harnesses back in behind the glove box and connected the vacume harness back up on right side of hump.I also felt the lines on the heater core at the box behind the glove box which where warm, so I know its circulating. Just dont understand what happen. Any Suggestions?

the.hogman

Sounds to me like you have air in the heater core as opposed to coolant. Be sure to properly burp the system and remove any air pockets and you should be good to go. Keep us posted.

tswcoaltrain

I thought about that. I didnt do that when I finished the installation, however I drove the truck 50 miles at interstate speed this morning then checked the aluminum lines to the heater core about 30 minutes after I got to work and the lines where still warm so I figured it was probably circulating. I guess its possible though. I didnt figure it needed to be blurped being a vented system to the overflow but maybe that will fix it. However my luck usually sux.

tswcoaltrain

Has anyone else had this problem with air trapped in the core after installing a new one????

GKS

What did you find out about your system? Did you burp it? and did that work?
I did the same replacement last summer but now have no heat.

mrclean

I've done three of these so far, and never had that issue, although that doesn't mean it couldn't happen.....
Can't hurt to try to burp it though. Park it nose-up or put it on ramps, remove the radiator cap. Start it and let it come up to temp......should be enough to dislodge any air if there's any in there......but your 50 mile ride on the highway should have cleared it out anyway.
Check the operation of the blend door.....this is likely the problem. Turn the key to "on" and cycle the temp control from full cold to full hot and listen for the door to thump against the stops.......if it does not move, it's 1) stuck, 2) the plastic coupler between the motor and blend door is broken, 3) the blend door motor is inop.

Jason Denney

So I have 07 cummins 6.7 I've changed water pump thermostat but heat only gets warm while driving. What am I doing wrong? I've burped the system with nose of truck raised so now I have a lil heat while driving but Luke warm while idling

GKS

This thread is referring to 5.9 cummins engines. The 6.7 you have, and I now have, has a place to burp the system. Its located on the passenger side above the EGR cooler.
theres a pipe at the highest point of the engine with a nut to remove to allow air out while filling. You’re supposed to open at that bleed point while filling. Fill until coolant comes out of that spot and then close it. Driving it will also work any air from the system. If you decide to drive it to get the air out, carry anti freeze with you and add as needed if necessary.