Vacuum line help

[xeqshnr]

I was pokin around under the hood of my Yukon today and noticed a small vacuum line that wasnt connected to anything. It comes out of what appears to be some kind of inline valve on the heater hoses. I had a buddy check his 98 pickup and it doesnt have the valve on there. He also said he had never seen one setup like mine. Heres a pic of the valve, any help would be greatly appreciated.

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

 

[JenneK]

Yeah, that thing will open and shut the flow of coolant to the heater core depending on the temp called for in the cabin. It's controlled via vacuum pulse.

Damn...I just bypassed by heater core and I can't recall where it connects... sorry.

 

[xeqshnr]

Thats kind of what I figured. ButbI.cudnt find where to hook it up. I found a place for another vacuum hose but it looks like its for one of those small hard lines. Heres a pic of it. That piece is different on the 98 pickups also.

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

 

[retorq]

On my 95 that vacuum connected to an electrical connector on the AC evaporator bracket. Should be the same or close on yours ...

 

[gpracer1]

Goes to a vac solenoid between the engine and receiver dryer, mounted to the firewall.

 

[xeqshnr]

Thanks guys I will check it out

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

 

[BattelWagun]

Thats kind of what I figured. ButbI.cudnt find where to hook it up. I found a place for another vacuum hose but it looks like its for one of those small hard lines. Heres a pic of it. That piece is different on the 98 pickups also.

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

I believe this is part of your EVAP system...

 

[xeqshnr]

Thats what my buddy called it. I couldnt remember what he had said.

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

 

[BattelWagun]

Thats what my buddy called it. I couldnt remember what he had said.

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

Yep, that actually vents fumes from the gas tank back into the manifold to cut down on unused emissions. They've been known to be very finicky, so I wouldn't play with it. Very costly to replace too...

 

[xeqshnr]

Goes to a vac solenoid between the engine and receiver dryer, mounted to the firewall.

Found it thanks!

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

 

[knoslf]

Found it thanks!

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

Hey xeqshnr I know this is old but did your heat work before you connected that vacuum line? And do you know what the line on top of the one you connected(to the piece on the firewall) goes to?

 

[xeqshnr]

My heat worked months before. I had just got with replacing the intake gaskets and it was the middle of summer so Idk if the heat worked before I reconnected that line. And I really dont know for sure what the other one is for, sorry

Sent from my SAMSUNG-SGH-I997 using Tapatalk 2

 

[Harry Hood]

Just replaces this HVAC valve on my Tahoe and with the line connected my heat does not work.

With it disconnected it works perfect.

Anybody an idea of why this is?

 

[east302]

The vacuum line on the heater control valve connects to a solenoid on the firewall. From what I gather, when the solenoid is energized vacuum is applied to close the control valve, closing off coolant flow to the heater core. I've read that this is supposed to happen when the a/c is on, but I'm not seeing that on the wiring diagram. It looks like voltage is applied when the temperature dial is set to the cold detent (max) setting.

Maybe someone else knows, but I'd look to see if you're getting 12V to that solenoid with the temp dial not set at the cold/max detent. If you are always getting voltage and energizing the solenoid, then the problem may be in the hvac control panel.

Also, with the temp dial not set in cold detent, unplug the solenoid (with vacuum line connected) and see if you get heat. That, to me, would indicate that the solenoid is bad.



Sent from my iPhone using Tapatalk