Heater not working and only blows cold air from top defroster vents

Tiny
SHADETREEMECHANIC
  • MEMBER
  • 1991 DODGE CARAVAN
  • 150,000 MILES
I've flushed the heater core (both hoses were hot, but tried it anyway) but still get no heat, thinking that was the problem. Coolant is topped off. But the air only blows cool from the top vents, nothing from the front vents and very little from the bottom vents. Any ideas?
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Monday, December 12th, 2011 AT 5:16 PM

4 Replies

Tiny
FIXITMR
  • MEMBER
Check blend door operation it's up over gas pedal area of HVAC.
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Monday, December 12th, 2011 AT 5:31 PM
Tiny
SHADETREEMECHANIC
  • MEMBER
Thanks fixitmr.I'll see if I can check it tonight and let you know.
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Monday, December 12th, 2011 AT 7:40 PM
Tiny
CARADIODOC
  • EXPERT
Hi guys. Once you figure out the mode operation, there was a common problem that causes it to blow only cool air. The clue is that both heater hoses are hot so you know it's circulating hot coolant and should be blowing hot air. An additional potential clue is you won't hear the nice "thump" of the temperature door when you slide the temperature lever back and forth.

If the air doesn't switch to different outlets, look for a broken or disconnected vacuum hose under the hood. When the vacuum supply is lost to the heater controls, the system is spring-loaded to go to defrost so even though your feet might freeze, the windshield will be clear.
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Monday, December 12th, 2011 AT 10:16 PM
Tiny
SHADETREEMECHANIC
  • MEMBER
Well, I checked the blend door & it works fine, I can hear the thump. Come to find out that someone had replaced the heater control valve a while back (it's my sister's van and she couldn't remember when she got it worked on), but there seems to be an extra vacuum hose that comes out of the firewall and plus into nowhere, so I'm assuming that the line that's messing up her heater operation. The other hose that comes from the firewall connects into the control valve and it you can see that it opens and closes the valve as you turn heater off & on. Now I have the task of location a diagram that shows where all the hoses are supposed to connect. One odd thing.I switched the hoses to go into control valve to see what would happen. When I connect the one I found loose into the control valve some heat does blow from defrost vents but doesn't operate the valve. Other than that still no air from other vents. Still searching.
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Wednesday, December 14th, 2011 AT 8:22 PM

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