Heater Core Replaced, Now Blows Cold Air

[CVD]

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?

[ILVMYGT]

My HVAC also has a water shut of valve with a vacuum line going to it like in the picture. On my HVAC it turns the coolant flow off to the HVAC only when you put the Unit on Max AC. Other than that it has no effect on the heat. I would determine what it does before I disconnected it.

[I_rv]

pull that green vacuum line off water valve, no vacuum gives full heat,you should see actuator arm move if not valve is stuck

[dougrainer]

I guess I don't understand WHY that so called mechanic NEVER checked his work. Doug

[Chum_lee]

Some heater core manufacturers use small plugs at the supply/return connections to the heater core to prevent debris from entering prior to installation. Obviously those plugs should be removed prior to installation.

Chum lee

[CVD]

Problem solved. There was a 'restrictor' in each hose connection for the new core, which was blocking coolant flow. Don’t know exactly what this restrictor was intended to do (or why it wasn’t obvious the lines were blocked with them in); but with them removed the heater system is now working. Not entirely thrilled with the mechanic, as I can’t imagine why this wasn’t noticed with the core installation. But no damage done, all is OK now.

Thanks for the suggestions (I learned a little about the vacuum pump),

[dougrainer]

THAT is your vacumm pump. That open hose is normal. You should be able to remove the hose that leaves and goes to the reservoir and the pump should RUN. If it does not, either the fuse is blown or the pump is bad. Doug

[CVD]

Thanks for the feedback.

1) I don’t think it’s an air pocket. Since the heater core install, I’ve driven it 100 miles, camped 3 days, and 100 miles back; with no change in coolant level in the reservoir.

2) I let it idle for 10 minutes (engine temp gauge just started to move, so it heated a little). I turned heater knobs on, and felt both hoses at the core. Hoses stayed cold.


3) I talked to the mechanic. He did nothing more than Doug said - disconnected the two hoses, installed the new core, and reinstalled the hoses.

4) When looking at it more closely, I noticed a vacuum box a couple feet away from the core. One house came out of that box (and into the firewall). A 2’d vacuum nozzle (probably incorrect term) from that box was unused. I looked for a loose hose in the vicinity and found none. Does this make sense to anyone?

In pic below, heater core on left, vacuum box on right has two nozzles, upper one has hose, lower one (white) is open.

[dougrainer]

1. IF the Mechanic turned off the engine area water valves--NOT a very smart mechanic. All you do is use needle nose vice grips and crimp BOTH lines at the area of the heater core to prevent leakage and coolant loss
2. DOUBT you have an Air Pocket. I have replaced over 50 Class A heater cores over the years and have NEVER had a Air pocket.
3. Odds are that Green VACUMM line is not opening the water valve, BUT, if so, it will take forever for those water lines to get HOT if there is NO coolant circulating. Put the dash control to HOT and pull the green line. If NO vacumm, that is your problem. Remember, Diesels have a 12 volt Vacumm pump, usually located within 2 feet of the Heater Core box. There will also be a round ball vacumm reservoir close by. You should be able to hear the vacumm pump running as it is loud and vibrates. I will bet the loss of vacumm is the PUMP is not running. The Pump is NOT a Chassis(frtliner) part. It is installed by the OEM RV maker. Doug

[eHoefler]

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.

[rockhillmanor]

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?

[amxpress]

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

[Krusty]

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.

[Tim_Nowicki]

One would think that the mechanic would test the system before it goes back to the customer. Apparently not.

Tim

[slickest1]

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.