No Air Volume on heat... Lots on Cold

[bob69302]

Hello,

Please don't flame because I have searched this forum and others and even Google, but I come up empty!

Let me start by staying the fan speed positon switch (and resistor) work perfectly in each position.

I have an 81 Bronco and with the tempature lever on hot and the mix lever in any position (floor, DeForest, vent, mix...) there is almost no volume of air out of any vent.

With the heater lever on cold and the mix lever in any position (floor, defrost, vent, mix...) there is a Lot of air blowing out.

The tempature lever is affecting the volume of air and I can't figure out what's blocking the volume of air with the tempature lever in the hot position. I installed a new heater core and it wasn't plugged at all.

Any tips would be greatly appreciated .

Thank you all,
Phil

 

[miesk5]

Yo Phil,
Welcome!
Bad vision day here causing me to get confused as I try to match yiur description with the 81 EVTM, sorry!
The HVAC Blend Door could be stuck. It is cable operated via the Control Panel Lever.
Blend Door directs air through or around heater core. When temperature blend door is @ Cool position NO AIR Flows throuh Heater Core

Normally, when the temperature control Lever is moved to the extreme WARM position, all air is directed through the heater core.

See this flow diagram from 1981 Bronco Workshop Manual.

Door Locations in Parts Break-Out Diagram in 80-86; temperature blend door, vacuum motors, heater core, upper & lower plenum depictions, etc.
You have to pull either the heater core or the evaporator core to see the blend door. Obviously, the heater core is easier, but you don't have to open the A/C system to pull the evap. out.
Source: by HawkRdr

1981 Bronco Dealer Brochure by Gary @ 1981 Bronco Brochure - Gary's Garagemahal (the Bullnose bible)

1980-1986 Bronco/F Series Fasteners by Gary

1980-1986 Bronco/F Series Carburetors, Chokes & EFI by Gary

1980-1986 Bronco/F Series Specifications by Gary @ Axle Ratios - Gary's Garagemahal (the Bullnose bible)

Differences in 1980-1986 Bronco/F Series by Gary

1981 Bronco/F Series Electrical & Vacuum Troubleshooting Manual (EVTM), partial via Gary @ 1981 EVTM - Gary's Garagemahal (the Bullnose bible)

EEC III Testing, etc @ http://web.archive.org/web/20101222172609/http://home.comcast.net/~TommySpace/EEC3.html by Tommy

Partial Chilton Manual for 1978, 1979, 1980, 1981 Bronco. Scanned by broncocity.com @ https://web.archive.org/web/20130419152159/http://www.broncocity.com/66-81manual.htm

1981 Bronco Advertisement @ Ads0002.jpg

AL