Air out of vents is still hot - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Kaptain Kadian · 10-23-2016, 10:59 PM

I have disconnected the ac from my truck and have replaced the heater cut off valve and the air that is coming out of my vents is still hot. I don't expect it to be cook, but it still feels like heater hot. How hot is the air supposed to be coming out of the vents when you don't have the ac hooked up, but the heater controls are set to ac?

barry1982 · 10-23-2016, 11:42 PM

I had a similar problem a few years back. Turns out a fairly large nail fell down one of the defroster vents, and got stuck in the heater box. This prevented one of the little doors from closing completely, and allowed cold are to mix with hot from the heater core.

Kaptain Kadian · 10-24-2016, 12:25 AM

Thanks for the reply, but I recently replaced the diverted box under the dash and cleaned out all debris. That all should be working now. I replaced all the vacuum lines and made sure they are all plumbed correctly as well.

67 chevelle · 10-24-2016, 07:31 AM

try bypassing your heater hoses to see if that is it , if it is maybe the diverter valve is defective

Kaptain Kadian · 10-27-2016, 06:02 PM

How can I test the vacuum system to see if it is working?

firedemon · 10-27-2016, 07:23 PM

on some of the valves if theyre hooked up backwards the pressure will open the valve

Andy4639 · 10-27-2016, 11:10 PM

I have disconnected the ac from my truck and have replaced the heater cut off valve and the air that is coming out of my vents is still hot. I don't expect it to be cook, but it still feels like heater hot. How hot is the air supposed to be coming out of the vents when you don't have the ac hooked up, but the heater controls are set to ac?

Going by what you said it sounds like the difram is either the wrong one are it's bad. These trucks had 2 kinds of vacuum valves. Vacuum applied to one valve opened it. Vacuum applied to the other closed it.
The 2 valves look the same and the only way to know for sure is to apply vacuum and see if it opens are shuts.

10-23-2016, 10:59 PM	#1
Kaptain Kadian Registered User Join Date: Mar 2014 Location: Broken arrow Posts: 211	Air out of vents is still hot I have disconnected the ac from my truck and have replaced the heater cut off valve and the air that is coming out of my vents is still hot. I don't expect it to be cook, but it still feels like heater hot. How hot is the air supposed to be coming out of the vents when you don't have the ac hooked up, but the heater controls are set to ac?

10-23-2016, 11:42 PM	#2
barry1982 Registered User Join Date: Oct 2015 Location: Waskatenau, Alberta Posts: 259	Re: Air out of vents is still hot I had a similar problem a few years back. Turns out a fairly large nail fell down one of the defroster vents, and got stuck in the heater box. This prevented one of the little doors from closing completely, and allowed cold are to mix with hot from the heater core.

10-24-2016, 12:25 AM	#3
Kaptain Kadian Registered User Join Date: Mar 2014 Location: Broken arrow Posts: 211	Re: Air out of vents is still hot Thanks for the reply, but I recently replaced the diverted box under the dash and cleaned out all debris. That all should be working now. I replaced all the vacuum lines and made sure they are all plumbed correctly as well.

10-24-2016, 07:31 AM	#4
67 chevelle Registered User Join Date: May 2013 Location: WEST PALM FLORIDA Posts: 1,174	Re: Air out of vents is still hot try bypassing your heater hoses to see if that is it , if it is maybe the diverter valve is defective __________________ 68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive

10-27-2016, 06:02 PM	#5
Kaptain Kadian Registered User Join Date: Mar 2014 Location: Broken arrow Posts: 211	Re: Air out of vents is still hot How can I test the vacuum system to see if it is working?

10-27-2016, 07:23 PM	#6
firedemon Registered User Join Date: Jun 2015 Location: @ Posts: 890	Re: Air out of vents is still hot on some of the valves if theyre hooked up backwards the pressure will open the valve

10-27-2016, 11:10 PM	#7
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Air out of vents is still hot I have disconnected the ac from my truck and have replaced the heater cut off valve and the air that is coming out of my vents is still hot. I don't expect it to be cook, but it still feels like heater hot. How hot is the air supposed to be coming out of the vents when you don't have the ac hooked up, but the heater controls are set to ac? Going by what you said it sounds like the difram is either the wrong one are it's bad. These trucks had 2 kinds of vacuum valves. Vacuum applied to one valve opened it. Vacuum applied to the other closed it. The 2 valves look the same and the only way to know for sure is to apply vacuum and see if it opens are shuts. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.



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