Heater won't turn off

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tndt1

Active member
Joined
Aug 18, 2011
Messages
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Location
Biloxi, MS
My Car
1973 white/white/white convertible, 302 V-2
Hi all; I have a 73 Convert with a 302 and A/C. Problem: when I turn the selector to off, the air is directed up through the defrost. (And seems stronger)

Also I have no vacuume on the Biack & purple line coming out of the firewall to the "dohicky"on the heater hose.

I also feel heat coming out of the floor, with the selector on cold,

Any help???????

 
well the heat keeps coming out because the heater control valve isn't closing.

you can test vacuum motors by themselves using a vacuum hand pump to see if they are working correctly.

but you need to chase down why you are not getting vacuum to the motors.

usually the climate control arm that controls the vacuum signal has got crud inside it and that had stopped up the vacuum getting to the motor. you will need to pull it out of the car to work on it, so it might be a good idea to test the motors first just to make sure they are working. that way you know the problem is inside the control block in the climate control manifold.

there is a vacuum plug junction that we call the octopus this is connected to the rear of the climate control manifold.

basically its a large block of rubber with all the vacuum lines running out the rear to feed all the vacuum motors behind the dash.

when you service the control manifold you will want to inspect these rubber hose manifold to make sure nothing is cracked from age and leaking vacuum signal. it can be a source of idle vacuum leaks and running problems.

once the climate control manifold is removed from the lower dash you can inspect it and try to clean it out using compressed air and electrical cleaner, a pipe cleaner would not hurt. each vacuum tube should be clear so when you move the selector arm to different points you can blow through a hose connection and have to come out the black vacuum control line which is the master vacuum feed signal. if you find you cannot blow through one of the veins then you have most likely found the source of the clog.

in your case it appears that 2 lines are clogged.

i would also take the time to inspect your vacuum reserve canister in the engine bay on the passenger side shock tower.

attach a tube and blow through the inlet on the vacuum can then try and suck air out,, if working correctly the air will only flow one way. if you can move air into and out of the vacuum canister then the reed valve inside is blown, replace the canister with a new one.

one source of clogged up A/C vacuum systems is carb backfires all you need is one and it can blow the reed valves and send junk into the climate control system, it can also damage the vacuum motors.

now usually the heater control valve dies from the coolant and heat eating it, so again i would test it first. you can close it manually but i would try hooking up a hose and then either use a vacuum hand pump or your mouth to create a vacuum and see if the valve moves.

if later on the valve works but the heat will still not turn off, that means the little valve inside the center of the heater control valve has rotted away, so i would just replace it.

testing each vacuum motor can be done with the dash in place you just need a long hose to reach them and long arms and fingers.

most likely you have a clogged up climate control vacuum manifold causing the problem Worst case you will need to replace it from a donor car and make sure it works before install.

I had to replace my original as nothing i did would get the clog out.

any who you have some diagnostic work to do this weekend, and again if the vacuum motors are all working and not leaking then start thinking about pulling the octopus and taking the center dash apart to get the climate controls out of the car and on the bench for cleaning or replacement.

 
What a great response. thank you so much it'll be awhile before I can reply I've got a lot of testing you give lol.

 
Well...... I blew it all out, checked all the actuatiors checked the incoming vacuume off the manifold (ok) and stil no change. It still won't shut off in the off position (goes to defrost) slight heat through all the vents with the slector in the "cold " Position, A/C blowing "cool" air. (System charged fully) Checked the electrical on the blower motor ristior. and that was ok, any more ideas???P.S. I guess I screwed up this time I switch the two wires alongside the octopus, blew a fuse, I replace the fuse, and now the blower won't work??????????

 
Last edited by a moderator:
pull the fuse sand the contacts and try again, sometimes you get a bad contact.

also check the connecter behind the fan switch on the climate control face plate sometimes it pops off a little.

you checked all the motors by themselves and they worked?

is it possible somebody hooked up the vacuum lines incorrectly?

now in the off position with the fan running it will just loosely blow air around usually it comes out more from the defrost vent.

the big thing is testing to see if the 'floor' 'vent' 'defrost' positons all work.

'MAX' is just A/C cooling but the fresh air vent to the cowl closes off with a flapper.

now the Hot/Cool lever isn't fully vacuum controlled, there are manually adjusted flappers when you throw that switch via a cable to the front of the a/c box, so make sure when you move the selector that the cable is moving the lever arm.

you may just want to replace the heater control valve at the firewall. i assume you tested it and it moved, but i may not be working internally they rust inside and the valve falls apart inside.

so basically the top lever is controlling where the air is going, Off just sort of blows air all over because all the flappers are shut, honestly it is a stupid not sure why ford marked it. floor shoots air into the footwells, and defrost at the defront vent under the window.

everything inbetween those 2 points just makes more or less heat go to the floor or defrost.

this is the one vaccum motor with a top and bottom inlet vacuum tube.

A/C turns on the compressor you can run it hot or cold it just takes the humidity out of the air.

MAX just closes the fresh air intake flapper. vacuum motor on passenger side right side behind glove box. (white vacuum line from memory)

now Hot and cold lever does the most. there is a manually moved flapper plus vaccum moved flapper. the vent vacuum motor is used i think that is the red line from memory

on hot the heater core bypass is off and the heater control valve is running, and the evaporator core temp sensor is off.

move that selector towards cold, and the flappers manually start to close and the bypass for the heater core slowly turns on as the heater core is slowly pinched off in stages from the heater control valve.

 
do you know what the two electrical connections on the passenger side of the octopus are for one appears to be yellow and the other light green

 
forgot another thing, there a plunger button on the manual cable control on the front of the A/c box, that can go bad, and not allow the heater control valve to work. when you pull the hot cold lever over the little button plunger should push in and that branches off to two vacuum motor. (its been a few years now so i'm fuzzy on it)



the two electrical connections on the passenger side on top of the heater box are for the evaporator core freeze sensor. when the ac is working the evaporator can freeze into a block of ice, and the sensor kicks off the A/C compressor like emergency shutdown to prevent pump damage.



here are my old heater box photos

http://s1031.photobucket.com/user/72hcode/library/Heater%20Box%20AC?sort=2&page=1

 
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