The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Heater off But Heat Sneaking Through Bottom Vent.. Lil help.

tucsonjwt · 05-20-2015, 06:02 PM

Keith can verify, but I think GM in the 70s came up with the "flow thru ventilation" idea which meant that the fan was always on low for improved ventilation, and possibly safety.

As far as I can tell, the hot coolant always circulates to the heater core, so it has heat- but that heat is not sent through the ductwork, unless the foam on the duct doors is worn out, which it was in all of the 3 squares I have owned.

I don't like vacuum controls because I think there is too much unreliable and potentially leaking vacuum points in these old trucks. I don't know why there are vacuum controls in vehicles when electric/electronic controls are much more predictable and reliable and don't affect other systems when they fail.

I do like the idea of the cable controlled valve for those who have big temperature swings during a single day. Any close up pictures of how that valve operates and where to get one? My concern is that the specialty valves I have used are not sturdy enough and leak over time. Plumbing valves need only about 1/4 turn for on/off (globe valve, not gate valve.)

05-20-2015, 06:02 PM	#18
tucsonjwt Registered User Join Date: Jul 2007 Location: Tucson, AZ Posts: 3,198	Re: Heater off But Heat Sneaking Through Bottom Vent.. Lil help. Keith can verify, but I think GM in the 70s came up with the "flow thru ventilation" idea which meant that the fan was always on low for improved ventilation, and possibly safety. As far as I can tell, the hot coolant always circulates to the heater core, so it has heat- but that heat is not sent through the ductwork, unless the foam on the duct doors is worn out, which it was in all of the 3 squares I have owned. I don't like vacuum controls because I think there is too much unreliable and potentially leaking vacuum points in these old trucks. I don't know why there are vacuum controls in vehicles when electric/electronic controls are much more predictable and reliable and don't affect other systems when they fail. I do like the idea of the cable controlled valve for those who have big temperature swings during a single day. Any close up pictures of how that valve operates and where to get one? My concern is that the specialty valves I have used are not sturdy enough and leak over time. Plumbing valves need only about 1/4 turn for on/off (globe valve, not gate valve.)