No heat... Heater valve issue?

[Shibbershabber]

99 Yukon...

Suddenly no heat

Noticed the hoses are hot up to the valve but cold on the other side.

The hoses, valve and heater core are all a few months old and worked well after install.

I manually operated the lever and ot all moves freely. Sometimes moving it manually can,get,the heat on but not always.

I tried to disconnect the hose thinking maybe that would bypass.... But no.

Impossible to get condensation off windows and drive like this.



Is there something else I should look at?

A way to bypass the operation of the valve, short of just removing it.

What happens id I just cut it out and run straight hose to the core?

 

[Denali Brad]

Had a 93 with the same issue, try pulling off the heater hoses and backflush the heater core.

More than likely, you've got rust flakes clogging the heater core.

 

[Shibbershabber]

There is no hot water going into the core, the valve is blocking it.

 

[Danny3737]

It’s possible you may have a blockage where the water goes in to the core. If you remove the valve ( if that is the problem ), you will have 100% heat all of the time. I would still back flush just to be sure.

 

[OR VietVet]

Likely this valve: https://www.rockauto.com/en/moreinfo.php?pk=84579&cc=1355510&jsn=922 but there is a valve solenoid as well: https://www.rockauto.com/en/moreinfo.php?pk=1990462&cc=1355510&jsn=925

 

[OR VietVet]

If the hoses on one side of the valve are hot and on the other side of the valve are cold, as he said, the valve is not opening to allow for coolant flow. He may still need a flush of the heater core or replacement but the coolant has to get past that valve to work.

 

[Shibbershabber]

The core & valve are new.

I'll have a look at that solenoid this weekend

 

[OR VietVet]

I bet you have a Dorman valve on there don't you? Dorman=Junk.

 

[east302]

The valve closes when the solenoid on the firewall under the accumulator is energized. There is a vacuum line running from the solenoid to the heater valve, the solenoid being energized when the temperature dial is set to the “max” detent to maximize a/c performance.

The solenoid valve has a hard vacuum line that runs across the intake and connects to the PCV fitting.

When closed and vacuum applied, the plunger at the bottom of the heater valve is pushed in/up or depressed. If it’s depressed, then either vacuum is being applied or the valve is stuck somehow.

With ignition off, the plunger should be down (valve open).

It sounds like you’ve already done this, but pull the vacuum hose from the valve and see if it opens. With no vacuum, you should be able to easily push the rod up with it springing down to the open position on its own. If it does, then check to see if the solenoid connector is getting voltage when the temperature dial is not at MAX position. It shouldn’t. Just use a meter between the two wires in the connector.

You can remove the valve and run hoses straight to the heater core lines. Only the Tahoe and Suburban used the valve. Pickups did not.


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[east302]

I bet you have a Dorman valve on there don't you? Dorman=Junk.

Don’t get me started, lol


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