I just replaced the heater core in my 78 F250 ranger camper special with 429/c6 it also has factory air. Everything worked properly at the time the repairs were made. I also changed out the little vacuum motor that is inline in the heater hose. It was frozen, but I still had heat. My AC guru suggested I replace it as he tested it and it was bad. FWIW the new vac motor is plastic(of course) and I cannot see it operate as it has no external moving parts. Now Ac works and I need a little heat in the mornings.

After all this I have no heat. Sometimes it puts out some heat and sometimes it does not? I have yet to identify anything in my drive routine that is a tattle tale. Any suggestions on how to properly work through this? Can I eliminate the inline vac motor on the heater hose? Will that cause any problems?

TIA just want reliable heat! Todd

 

So it seems that I have heat until I move the lever to vent position, then back to the heat position. Any body have any thoughts?

 

That is a heater control valve. The purpose is to shut the water supply to the heater core off when in the A/C mode.

 

Could the cable be hooked up wrong or not adjusted right and closing off instead of opening the flap door or temp.

 

ranger, would you suggest pulling the heater control valve and try it out that way? I wonder if it is punky or possibly working backwards? It all worked just as soon as the heater core was replaced.

fridge, I believe the doors are opening as required. The one on the right side floor board opens and closes as the lever is moved from one position to the other. The flapper door inside the heaterbox I assume is working because the cable moves the lever that should move the door all moves freely. This is all on top of the heaterbox inside the engine bay.

Todd

 

D4AZ18495A .. Heater Control Valve (Motorcraft YG136)

Available from Ford...and the reason why is...it's been a best seller for decades.

MSRP: $28.72 // FTE sponsor: Y2KFORDPARTS.COM price: $17.23.

Fits: 1974/79 F100/350 with factory installed integral A/C only.

Fits: 1971/78 Passenger Cars / 1978/79 Bronco's with factory A/C.

This valve is a total POS ... which was/is notorious for failing!!

Usually the POS is stuck closed or stuck half way open.

It's vacuum operated. The top of the valve should have a nipple where the vacuum hose fits to.

The genuine Ford valve is metal on the bottom, plastic on the top.
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With factory A/C, there are four vacuum motors on the A/C/Heater plenum chamber that open and close the various doors.

2) D7TZ18A318A .. A/C/Heater Vacuum Motor (Motorcraft YH308)

One of these two motors operates the recirculating door, the other operates the outside air door. Fits: 1977/79 only.

1) D3TZ18A318A .. A/C/Heater Vacuum Motor (Motorcraft YH219)

This motor operates the heater door and is color coded red/yellow. Fits: 1973/79.

1) D3TZ18A318B .. A/C/Heater Vacuum Motor (Motorcraft YH218).

This motor operates the heater/defroster door and is color coded blue/orange. Fits: 1973/79.

All these motors are controlled by this:

D5TZ19B888A .. A/C Vacuum Control Selector Valve Assy (Motorcraft YH285)

This mostly plastic valve attaches to the backside of the A/C/Heater control panel, has staggered tubes where all the vacuum hoses connect to.

The "kicker" switch that turns the A/C off/on is mounted on top of it.

When you move the levers on the A/C/Heater control panel, this valve opens one door and closes another. At least...that's the way it's supposed to work.

Check all the ends of the myriad vacuum hoses, as these hoses tend to harden up and crack apart.

One vacuum hose leaking is all that's required to keep the system from operating properly.

 

You sir, as usual have gone above and beyond! I am almost sure the vac motor the parts store sold me is at the very least incorrect, and possibly not working on top of that.

I will sort this out in the next week if things go good for me!

Thanks

 

BILL; You did such a fantastic job for Todd, maybe you can find it in your heart to assist me. I am having trouble getting the AC to blow cold. Converted to 134 five years ago, and recently I notice warm air, let up on the gas and it gets cold. So I am assuming one or more vacuum leaks. You mentioned D5TZ19B888A, AC vacuum control selector valve assembly. Is this the multi-ported plastic control with electric connector that sits behind the AC/heater panel on the dash? Next, are they still available anywhere? I have a 1974 F100 Explorer with factory air.

 

FWIW The heater control valve the parts house sold me was bad. I also discovered the factory connector at the resister inside the heating duct was fried. I managed to sort that out and fix it. Also found I had a bad fan speed switch. After I fixed all that the fan when out on a squeal. I highly advise anytime you have to get to the heater core on a factory AC truck, be satisfied that the heater blower motor is gonna last you till you die.

Todd