Hey guys. I have a 1971 Plymouth duster with a 340. The heat comes in cool/luke warm. I have a 180 thermastat in it. The coolant level is up to level too. What is making this come out cool? The fan blows just fine, its just the air is cool no matter how warmed up the car is. Any suggestions ?

Possibilities: the air blend doors could not be opened all the way, heater hoses on backwards, heater core partly plugged.

Where are the Air blend doors located ? and how would i close it, if its opened.

in the heater box under the dash. they are either cable or vac pod activated. There's 2 doors & manually move them & see if that takes care of you.

Well there was a door under the passenger side dash with a little lever connected to it that was open last time. i closed that and the heat was hot. But then it got cool again. Where is the 2nd door ?

Look for where the other cable connects to. one door directs air up to the defroster vents & the other door being opened a certain amt dilutes the amt of hot air for temperature control.

Yea the 1 i closed i had to tape close. It goes somewhere to the controls in the dash. But i have no clue where to even start looking for the 1 you are speaking about. What is amt ? and where should i look ?

the other one is more hidden somewhat but it is in the black heater box there. Can you trace the other control cable(the temperature lever) from the dash down to the box & open it all one way then all the other way & see if one of those makes it heat up.

Well what happened was the heat use to come out cool. So i closed that vent with the lever going up to the dash with tape and the heat got really warm. I was driving the other day and im guessing the tape came loose and the heat got cool again. I reset the tape so the vent was closed it got hot again and then out of no where cool. I checked the vent and its still closed.

No its cool now. = /

I started to celebrate too soon. can you see where the other cable goes to(from the temperature lever) & move that door

The only thing i see is the 1 with the lever that goes from the vent to the dash somewhere. The lever is medal. It goes to 1 of the controls in the dash. Thats the 1 i closed. I dont see the other 1 u speak of.

This car has no A/C right? On the dash there's 2 heater controls, does one says off-heat-defrost & the other says temp & you can slide it all the way over? & if not what do you have?

Yes that is correct. No there isnt AC. I have the Temperature thing all the way to warm and i have 2 dash bottons pressed in. defrost and heat if that helps.

with the temp lever all the way over to warm then the DOOR thats moved by that cable needs to be moved all the way over(not sure which way) & since you have DEF & HEAT buttons you dont have a second lever, the buttons direct vacuum to a vac pod on the outside of the door that moves the door open & closed or to a vacuum valve under the hood in one of the heater hoses It will have at least 1 small dia vac line going to it.

FWIW - basic non-ac: http://70duster440.com/HeaterBoxIllus.jpg

tremendously helpful. I thought there was 2 cables EDIT that only A/C had the vac pods on the heater box with the possible exception that A/C/non A/C both had the vacuum controlled shutoff valve in one of the heater hoses on the passenger inner fender under the hood.

My 71 Does not have any vacuum lines going anywhere. It's all cable actuated. Sounds like your heater core is plugged.