I had a leaking heater core replaced on my 99 Winnebago with a Freightliner XC chassis. No more leaks, but now the dash heater only blows cold air. I suspect my local truck repair guy (who knows heavy trucks, but necessarily RV systems), didn’t reconnect something properly. Here’s a pic of what I’m looking at. I imagine that “valve” on the heater hose (with the pale green wire) is what controls coolant flow through the core. Anyway to test it? Anything else I should check?

With engine running a few minutes, feel both heater hoses to see if they get hot. If not, no or little coolant flow. Possibly the vaccume controled valve you mentioned. If both hoses are getting hot, likely the blend door is not operating, possibly bumped off during the repair.

On the hose right behind that valve is looks like there is a cut-off valve. It would have sort of a slider arm that rotates 45-90 degrees and opens and closes the fluid access. Is that what I am seeing and if so, have you tried moving that to the opposite position?

Vaccuum should open that valve and let the coolant into the core. You can test it with a hand vacuum-pump. You should have vacuum there (can feel it if you put your finger over it) when you're calling for heat.

My Freightliner chassis has yellow shutoff valves for the cab heat water lines back near the engine. You might see if you have those and make sure that they are open.

cbeierl wrote:My Freightliner chassis has yellow shutoff valves for the cab heat water lines back near the engine. You might see if you have those and make sure that they are open.Like said above or follow the heater hose up to the engine there may be a valve type tap that is shut off. The mechanic may of shut it off so the antifreeze would not leak out while changing the core and forgot to turn it back on.

Heater Core Replaced, Now Blows Cold Air | Good Sam Community

All_I_could_aff
Explorer
Jan 02, 2017
With engine running a few minutes, feel both heater hoses to see if they get hot. If not, no or little coolant flow. Possibly the vaccume controled valve you mentioned.
If both hoses are getting hot, likely the blend door is not operating, possibly bumped off during the repair.
Bill_Satellite
Explorer II
Jan 02, 2017
On the hose right behind that valve is looks like there is a cut-off valve. It would have sort of a slider arm that rotates 45-90 degrees and opens and closes the fluid access. Is that what I am seeing and if so, have you tried moving that to the opposite position?
turbojimmy
Explorer
Jan 02, 2017
Vaccuum should open that valve and let the coolant into the core. You can test it with a hand vacuum-pump. You should have vacuum there (can feel it if you put your finger over it) when you're calling for heat.
cbeierl
Explorer
Jan 02, 2017
My Freightliner chassis has yellow shutoff valves for the cab heat water lines back near the engine. You might see if you have those and make sure that they are open.
slickest1
Explorer
Jan 02, 2017
cbeierl wrote:
My Freightliner chassis has yellow shutoff valves for the cab heat water lines back near the engine. You might see if you have those and make sure that they are open.

Like said above or follow the heater hose up to the engine there may be a valve type tap that is shut off. The mechanic may of shut it off so the antifreeze would not leak out while changing the core and forgot to turn it back on.
Tim_Nowicki
Explorer
Jan 03, 2017
One would think that the mechanic would test the system before it goes back to the customer. Apparently not.

Tim
Krusty
Nomad II
Jan 03, 2017
There is likely air in the system due to the long lines and the placement of the heater core. First check the coolant level and make sure it is full.
amxpress
Explorer
Jan 03, 2017
Like Krusty said, very likely an air pocket is not allowing circulation through the heater core. Touch both hoses where they enter the box, after the engine reaches operating temperature, if only one is hot , apply vacuum to the nipple where the green wire is connected. Oh, that's a hose not a wire. If the hoses still aren't hot to the touch, bring it to a shop that can bleed the air from your cooling system. Also make sure your water pump is circulating the coolant.
Good luck
rockhillmanor
Explorer
Jan 03, 2017
thermostat?

I've had work done on water hoses and then have the thermostat stick open from debris inside the lines that were opened and/or they stick from extreme heat pressure from why the repair was needed.

And with a heater core repair we always replace the thermostat at the same time. Did they replace yours?
eHoefler
Explorer II
Jan 03, 2017
Run the engine with the radiator cap loose, so the system won't build pressure. You may have to take it for a drive to get the air totally purged.