Hot in the front cold in the back.

[Z7195]

Hey everyone! You've all already helped me fix my 99 Tahoe and 95 extended cab numberless times. I've never actually had to post any questions. They've always already been answered. So, before anything thank you!

My 99 Tahoe, with the heater on, is blowing hot air out the front vents and defrost etc...but it's blowing cold out out of the vents in the rear. I've researched this a bit and I think I am more confused than when I started.

Thanks in advance for your help. Let me know if any other/more background information is needed.

 

[GoToGuy]

Does it have rear heat/ ac option?

 

[Z7195]

You can control the rear fan speed from the front, or you can select 'rear control' and the fan speed can be controlled by a knob above the rear seat

 

[Z7195]

I'm still researching this and am just now learning that some of these four-door Tahoes only have rear a/c and no rear heat. Is there a way to know for sure that I do not have rear heat?

 

[grampadirt]

If you have heat in the rear there should be three knobs of which one will be a blue to red dial,red being heat.You can also look under the vehicle,under the pass. side if you see four tubes going to the rear two of them go to the rear heater core.

 

[1998_K1500_Sub]

I'm still researching this and am just now learning that some of these four-door Tahoes only have rear a/c and no rear heat. Is there a way to know for sure that I do not have rear heat?

Well, one obvious way is to look up into the body cavity, behind the right-rear tire / wheelwell, to see what's plumbed there.

If you have both heat and AC, there will be four hoses... two high pressure refrigerant hoses for AC and two coolant hoses for heat. Those hoses travel up through the body into the air handler that's in the back of the vehicle. The AC evaporator and/or heater core (when so equipped) live in that air handler, along with the blower fan, etc.

This picture shows all four hoses (and it looks like a rat's nest) on my Suburban. Yours may look a little different if it has all four. It will look a lot different if it has only two. If you enlarge the picture you can see I've drawn circles around the AC and coolant/heat lines where they travel along the body near the wheel.

The brown paint visible is simply some primer I applied to the body panel behind the wheelwell. Originally it was painted the body color.

 

[Schurkey]

I'd be looking for the heater control valve under the hood. Don't these things shut off the coolant flow to the rear heat when the A/C is working?

 

[GoToGuy]

Yeah the solenoid controlled vacuum shutoff valve by heater hoses on firewall.

 

[Z7195]

Well no wonder it only blows cold air on the kids. It does not have rear heat!

The more I read, the more confused I got. Nothing to fix per se, but you saved my sanity.

 

[1998_K1500_Sub]

Don't these things shut off the coolant flow to the rear heat when the A/C is working?

IIRC they shut off coolant to the front heater core when, on the main controls, "recirc" is selected or the "cool/hot" knob is turned all the way cold.

Maybe I oughta go check before I mouth-off, the Suburban is out in the garage.

Coolant always flows to the rear.