Trying to convert an A/C heater box to heat-only

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Bill Crowell

Bill Crowell

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I'm trying to convert the A/C-type heater box (attachment) on my 1978 D-series truck to heat-only. I've removed the A/C evaporator. What do I need to do now in order to get fan air to flow through the heater core? Should I block off the round opening in the heater box through which the fan normally blows air, or would this block all air, including to the heater core? If I don't block off that round opening, will air still flow through the heater core? Thank you very much.

heater box.jpg
 
I'm not sure but do you have a valve on your heater hose ? If so either remove it or hook a vacuum line to your intake manifold so it stays open and let heat into the box.
I'm just guessing here .
 
I've got my heater control valve working fine. I'm only concerned with getting the fan to blow air through the heater core. I tried blocking off the round opening, but that blocked all air, including to the heater core. So I'm going to remove the piece of sheet metal that I've got blocking off the round opening and see whether it blows through the heater core then.
 
Not much hep here. If I had the thing in front of me, it's a matter of making sure "the doors" send air where you want. Removing the evap might affect that unless you use some material to seal where "it was"

There's also the possibility that some of the servos/ vacuum controls etc aren't working as they should
 
I've been running the original AC/heater box in one of my Darts since 1978 with the rest of the AC removed. Heater and defroster work fine with the original controls - I covered the AC duct to the old under dash AC vents, pulled the AC evaporator core so I could put caplugs in the firewall. No muss, no fuss.
 
I discovered the problem was that the heat and defrost door wasn't opening, so no air was blowing over the heater core. You do need to block off the big hole that flows air over the evaporator core that I removed, or else all the air will take that route. Viewed from the engine compartment, the air has to flow up the fan housing outlet that branches out from the motor housing at an upward angle toward the driver's side. Now I just need to figure out why the door is not opening.
 
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