RichC10

Problem, heater won't shut off. I've tracked it down to the wires for the heater control solenoid. I'm only getting 4-5 volts to the solenoid with the control set all the way cold. Zero volts all the way hot. Solenoid works when I apply 12 volts. Is the dash switch something that I could clean with contact cleaner, or is it a lost cause? Seems pretty pricey to replace.



Thanks in advance.

in2pro

RichC10 Welcome to the forum...

Lets get a bit more info to help you out here...

What year model are we talking about...

When you say heat won't shut off, we talking fan or the heat..

Keep in mind if your blend door is staying open, you will also get heat all the time..

RichC10

[QUOTE=in2pro;242419]RichC10 Welcome to the forum...

Lets get a bit more info to help you out here...

QUOTE]

Ooops, it's a 99 Suburban. Thanks for the response, I think I have it worked out. The problem was the hot water was not shutting off, always going thru the heater core. The fan and the blend doors work fine. After further searching the web, I found the solenoid is supposed to be getting 12 volts in order to shut off the heater core, so it seems the temp control dial is bad. Rather than spend big bucks on a new heater control, I just rigged a toggle switch to the solenoid. That makes the heat all on or all off, but I can live with that. The truck is only used to tow the boat in the summer, or drive in the winter when it's too cold to ride the bike.

tech2

glad you fixed it.

for others wanting info on this system...
there is no heater control valve on a 99 suburban. Coolant is continually flowing through the heater core at all times. the temp blend door is what regulates the heat.

the brown wire should have 12volts at the temp blend door actuator but it is not supplied its voltage from the hvac module rather the i/p heater /ac fuse.

the black wire is grd and the white wire should have a varying signal depending on the temp control dial position. The voltage change on this wiring is what causes the temp acutator to change the door position.

RichC10

There is a vacuum operated valve under the hood that diverts the coolant.

More Information for FOUR SEASONS 74781

No vacuum, coolant goes thru the heater core, with vacuum the valve closes and the coolant goes back to the engine. I've heard that 99 was an odd model, maybe some didn't have this system, but I haven't had any problem ordering parts.

tech2

ok. i seen these types of valves for rear heat systems, never for the front heater core on 0db2 or newer.

Where is the valve located; by the firewall near the hvac box?

RichC10

Ok, maybe I'm mistaken.... The valve is near the firewall right in front of the hoses going thru to the heater core. The coolant lines from the motor T off before the valve, I assumed that was for the rear heat. The way it is installed, it does divert the water to bypass the heater core. I didn't get the truck until it was 13 years old, so who knows, but it looked like the stock installation to me.

tech2

Was hard to get info but I found some "unclear" pictures on it and it does appear to be going to the front heater core. The valve is stock but can you confirm where all the hoses go.


From what you see...is the valve vacuum controlled and there is a electrical solenoid that controls vacuum to the valve?


I assumed the valve would be for the rear system...to close off coolant flow to the rear to provide quicker coolant warm up.

RichC10

Yes, the valve is vacuum controlled by an electrical solenoid. It is a cool little piece of engineering, but I'm old enough to remember when a simple cable connected the heater control to the valve. No wonder these things cost 40K new.

tahoe64gg

Just like to know if you got your problem solved? I disconnected the ground at the battery hoping for a computer reset, but no help here. Thanks for any advise.
Terry