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1978 blower motor w/Factory AC replacement

I’m trying to find a previous article on how to replace my blower motor on a 1978 F-150 with factory AC. I have read there’s an article that explains how to replace the blower from the passenger interior and not have to disconnect my evaporator coil. Can you help me find the article. I’m sorry but I have looked without any luck. Any and all help would be greatly appreciated. Thanks in advance for assisting me.
I found an old post that had a link to the article but it no longer works. I would really like to see the article because it sounds like someone took a great deal of time to put it together. Any help out there on this would be great.


Staff member
I found similar issues, but what I did gather is that you take the air box out of the interior. There is one bolt hiding behind the fender well though apparently. Gotta love the bright soul that thought that was a good idea... the fan location and the hidden bolt. Did see that taking the box on the motor side was NOT the proper way to do it.

Found one:
1978-79 With Air Conditioning

Do not discharge the air conditioning system.

Disconnect the battery cable, remove the carburetor air cleaner and partially drain the coolant system.
Remove the heater hoses from the heater core.
From under the hood, remove A/C hose support bracket from the cowl (one screw).
Remove the insulation tape from the expansion valve and sensing bulb. Then remove the cover plate and seal from the evaporator housing at the expansion valve (two screws).
Remove the glove box liner and remove the A/C duct by pulling from the instrument panel register and releasing the clip at the plenum.
Disconnect the right cowl fresh air inlet vacuum hose from the fresh air door vacuum motor.
Remove the evaporator rear housing from under the instrument panel. Then, remove the fresh air inlet tube from the evaporator rear housing ( 4 nuts and 1 bolt) and install one upper nut to retain evaporator housing-to-dash after rear housing is removed.
Disconnect wires from the de-icing switch and pull capillary tube out of evaporator core. Remove the de-icing switch mounting plate (four screws).
Remove two screws retaining plenum-to-dash (above transmission tunnel) and two screws to evaporator case and remove the plenum.
Install a piece of protective tape on A-pillar inner cowl panel, at lower right corner of instrument panel.
Then, remove the lower right instrument panel-to-A-pillar bolt and lower the center instrument panel brace, bolt and nut.
Position the instrument panel rearward and install the A-pillar bolt to hold the panel in the rearward position.
Remove four evaporator retaining screws.
Position the evaporator away from the case and secure it rearward and upward. Remove evaporator sealing grommet.
Remove heater core (3 screws retaining 2 plates).
Remove A/C-heat door (snaps off).
Remove A/C-heat door arm support (2 screws) and pivot arm retainer (1 screw).
Remove blower motor (2 screws) and remove blower motor. (see diagrams below).




Transfer blower wheel to blower motor and panel assembly.

Install door arm pivot retainer (1 screw) and door arm support (2 screws).
Install A/C/heat door (snaps on).
Install heater core.
Remove the retainer that held the evaporator away from the case, install evaporator and tube sealing grommet.
Install the plenum (4 screws).
Install the de-icing switch mounting plate, install de-icing switch capillary tube back into evaporator core and position blower wire grommet.
Connect blower and de-icing switch wires.
Remove upper evaporator case retaining nut and install the evaporator outlet (4 nuts and 1 bolt). Then, position the air inlet bellows.
Connect the right cowl fresh air inlet vacuum hose to the fresh air door vacuum motor.
Reposition the instrument panel, install the retaining bolts and remove the protective tape at the A-pillar inner cowl panel, lower right corner of instrument panel.
Install the right A/C duct assembly and install the glove box liner.
Install seal and cover plate to the evaporator case at the expansion valve.
Install insulation tape over the expansion valve and sensing bulb.
Install the A/C hose support bracket-to-cowl.
Connect heater hoses to the heater core assembly.
Fill cooling system, install the carburetor air cleaner and connect the battery cable to the battery.
Check blower motor operation.

We also have our own Ford service manuals uploaded courtesy of members as well. It is at the top of this and other forums.
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Thanks Fellro. You’re a gentleman and a scholar. I’ll let you know how it goes. I better get a heater core and be ready to replace it too along with the blower. It’ll be a few days before I tackle this.
I was successful using this write up. I now have a new blower mounted from the engine compartment and a new heater core. I reconditioned the best I could. Another problem I now have is the de-icing relay is not cycling the compressor off. My dash vent temperature is down to 30 degrees. For some reason my original de-icing relay would no longer engage the clutch so now I have no AC. I changed the relay and it started working again. A few minutes later the clutch disengaged and the replacement relay is not working now. I still had very cold air but no signal to run the compressor. What’s causing the relay to release the clutch. I’ll have to remove my cover under the dash to access the relay again. I bench tested my old relay and it appears to be working again. If you can lead me in the right direction I would greatly appreciate it. I plan to tackle it again tomorrow. Thanks


Staff member
I would check the pressure switches. One is for high pressure, one is for low. Either will turn off the compressor. The compressor is supposed to engage while the defrost is on, as it dries the air. Need to also verify what the pressure is, it can run for a bit, then draw down the low pressure side, trip the switch when it gets too low, then kick it off. Possible to also have a leak that allows it to get too low.
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1978 blower motor w/factory air

Fellro Where is the hi/low pressure switches located. When I look at the wiring I see the de-icing relay controls the clutch. I’ll look back at the wiring. I didn’t see the hi/lot switches and how they are connected. Thanks.


Staff member
They attach to the pressure and suction lines or other areas on the plumbing.
The deicing switch is possibly working as it should, keeping it from icing up the evaporator core. I don't find the pressure switches so may be a later addition for protecting the system.
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1978 blower motor w/factory AC

I’m trying to find a schematic for the wiring on this F-150. It’s all factory wiring. Maybe it will be in my big manual. I’m going cross eyed looking at this phone trying to find the clutch circuits. I’ll get back to it tomorrow and figure out why it’s not working. My blower is working great thanks to the write up. The AC was working great before I tore into the air box to fix the blower. When I find my problem I’ll come back and post it for your information. I appreciate you.
Hi Fellro. I managed to get my system running again today. I put my old De-icing switch back on and played with the “kick in and kick out” adjustments. It ran fine for a while but now and then the relay would fail. I could touch it and it would work. It’s not turning the clutch off and the lines start icing up. I could touch the moving part inside the relay and the clutch would stop and the cycle would work for a while. I noticed the pressure on the high side was a little low so I want to add just a little Freon to get the pressure up to about 225 or so and try that before I do anything else to the thermostat switch. What’s your thoughts on my response so far. Thank you for your guidance.

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