No heat has got me stumped

[teafreak35]

Here’s the problem: fan blows fine in both places but I’ve got no heat up front OR in the rear. Every now and then, front heat will blow the faintest amount of warm air and then go back cold.

Here’s what I’ve checked:

Vacuum - no leaks anywhere that I can tell. Pulled all hoses and visually checked and they all look fine. (From what I discovered, vacuum is only applied to front heater valve when cold setting is selected on hvac control panel. This makes me think that heater valve is open by default and vacuum is applied to close it when cold is selected). Therefore, it would appear to me that loss of vacuum would affect the rear heat but shouldn’t affect front heat.

Heater core - I pulled hoses and ran water through from water hose in reverse of normal flow. Everything came out clean and flow was strong.

Hoses - hose going into heater core does get hot to touch after vehicle gets to normal operating temp, but hose coming out of heater core never gets hot.

Here’s what I know. Radiator has a small leak in top drivers side corner. Coolant in overflow reservoir leaks down bc of this leak, but when you open the radiator cap, you can see coolant at bottom of fill tube.

I’ve read that a leaking radiator can affect heater function but don’t quite understand how. Is that my culprit here?

[chevymaher]

There is a water control valve that is junk new. Check that. And yes a leak may do it on these vans the heater core is higher than the radiator. So if the radiator is low it is way below the heater in front. Rear shouldn't be affected tho. Back to water valve.

Replace that with a ball check valve instant at least double the heat if it was working correctly in the first place.

[teafreak35]

Let me drop another bit of info that may clear up the rear issue. This just occurred to me. So the rear heat also has a control valve that is vacuum controlled. However, the vacuum has an electric solenoid above the valve. I’m assuming that when you turn on the rear heat switch in the cab, the solenoid is engaged and allows the vacuum to pass through. I suspect the reason the rear heat isn’t working is bc this solenoid is bad. I can bypass that solenoid with the vacuum line and get some heat out of the rear unit. That leads me to believe I might have two issues. The electric solenoid for the rear and the leaking radiator for the front. That sound logical?

[chevymaher]

Yes just time to test things.