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Discussion Starter #1
I promise I've searched and am not coming up with a good previous thread to help me. If there is one, please send the link and hit me with an imaginary hammer.

My AC/Heating Dash Selector is not functioning properly. It doesn't feel like it has "catch-points" on each section (Max, Normal, Vent, Floor, etc.). It is simply sliding through each section. Each section is also not working properly once the selector is hovering over the section - Example: When I slide all the way right to Defrost - The AC comes screaming out of the vents.

I'm going to have a look behind the Dash Selector Panel to see if something is loose, but wanted to check with the collective to see if anyone has any suggestions.

Thanks,

Brandon
 

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Yo Brandon,
See my Vacuum leak test in post #11 incl some jowens126 HVAC Control Panel pics/info @ https://www.fullsizebronco.com/forum/21-noobie-bronco-tech-questions-flame-free-zone/206824-help-dtc-codes-idle.html

Excerpt; One way to do a quick check is to grab a vacuum gauge. Some parts stores will loan you a gauge with refundable deposit.
The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .
When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.

One likely perp is described in "Outside Air Recirculation Door Vacuum Motor Hose Leak Replacement in 92-96 by John D; air blows through my Defrosters or my A/C switches back and forth when I accelerate" problem." @ https://www.fullsizebronco.com/forum/23-technical-write-ups/175808-how-i-fixed-my-c-vac-leak.html

FOLLOWING IN 92-96 BRONCO, may be similar to your 89;
"The function knob actuates a vacuum selector valve that controls the movement of the door.

In the NORM A/C, VENT, FLOOR, MIX and DEFROST positions, outside air is drawn into the system by the blower motor (18527). In the OFF and MAX A/C positions, the recirculation door is positioned so that outside air cannot pass into the A/C evaporator case (19897). In the case of MAX A/C, passenger compartment air is recirculated. In OFF position, blower motor does not operate.

Temperature Control
Temperature is controlled by a manually operated air blend door in the heater air plenum chamber (18471). When the temperature control knob is in the extreme COOL position (fully counterclockwise) all air bypasses the heater core (18476).

When the temperature control knob is moved to the extreme WARM (fully clockwise) position, all air is directed through the heater core. When the temperature control knob is between COOL and WARM (between full counterclockwise and clockwise), air is directed through and bypassing the heater core in rough proportion to the position of the temperature control knob between the extremes of its travel.

Blower Motor Control
Speed is controlled by a four-position heater blower motor switch (18578) and a heater blower motor switch resistor (18591) located in the A/C evaporator case upstream from the A/C evaporator core (19860).
The switch is used to select LOW, two intermediate, and HIGH speed settings. The heater blower motor switch is turned off by rotating the function selector knob to its OFF position.

A/C Switch
The air conditioning system is turned on and off by the function selector switch. When the function selector knob is positioned in any A/C mode (MAX or NORM), and the engine is running, electrical current flows through the A/C cycling switch (19E561) to the A/C clutch field coil (2987), the A/C clutch (2884) engages and the air conditioning system operates (providing ambient air temperatures are above a prescribed temperature). When the function selector knob is set in the DEFROST or MIX positions and the same above conditions are met, the A/C system will also operate. This allows the operator to select the proper air temperature (when the temperature control is adjusted) for defogging the windshield and side glass when necessary, by taking advantage of the dehumidification benefits of the air conditioning system. When the function selector is placed in any other position, current is stopped to the air conditioning circuit and the A/C compressor (19703) ceases operation."
 

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Discussion Starter #3
thanks for the quick/detailed reply.

I don't believe it's vacuum. I went through the entire system 2 years ago when air only went through defrost. All vacuum lines replaced and holding good/steady vacuum. But I'll check.

The Mode Selector Slider feels like there aren't any "catch-spots". It slides very free across the range and doesn't have notched spots below each Mode. Feels like the selector slider is broken or has become disconnected.

thanks for the assistance,

Brandon
 

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Although I have never looked at the back side of my HVAC controls on my 89, I had a similar situation with a Falcon. In that case, there was a broken pin that the levers pivoted on. I'm sure it's a completely different animal, but I suggest getting a look at mechanism while operating back and forth.
 

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I promise I've searched and am not coming up with a good previous thread to help me. If there is one, please send the link and hit me with an imaginary hammer.

My AC/Heating Dash Selector is not functioning properly. It doesn't feel like it has "catch-points" on each section (Max, Normal, Vent, Floor, etc.). It is simply sliding through each section. Each section is also not working properly once the selector is hovering over the section - Example: When I slide all the way right to Defrost - The AC comes screaming out of the vents.

I'm going to have a look behind the Dash Selector Panel to see if something is loose, but wanted to check with the collective to see if anyone has any suggestions.

Thanks,

Brandon
I have a similar problem with mine, even after working on it. And I've also verified all the motors move when vacuum applied to them via a hand pump connected to the vacuum harness. So you're not alone.

The lack of "catch" is, in my opinion, a function of the detents in the vacuum switch housing being very shallow coupled with deflection from the switch shaft when you move the selector slider. The shaft deflects and it deflects enough at an angle off of perfect vertical that the male portion of the shaft's detent system just skips over the female detents in the housing. The design doesn't look like it'll hold up over 30-40 years and likely was never designed to in the first place.

I have some pictures of my 80's unit disassembled at this thread here:

https://www.ford-trucks.com/forums/1589230-ac-max.html

I'd like to write up something on it, I just have to find some time to do it.
 

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Discussion Starter #6
Solved

I wanted to provide an update that the issue has been solved.

I had a chance to take the Climate Control Unit out to look at what was going on or why it was sliding.

Right away I found that the vacuum hose "header/adapter" module was not properly plugged into the female end.

I pushed and held them together and started sliding the Climate Control Mode Selector across the range and it started working properly. The notches at each mode also returned or came back.

I then took it apart again and the slider just "slid" across all modes without notches or catches at each mode selection.

I had to keep the adapter together or snug by installing a wire strap around it. This was the previous solution as I pulled out an old strap that had broken off and caused the current issue.

All is back together and good.

Thanks,

Brandon
 

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When replacing all of my vacuum lines I found a similar issue with the module behind the climate control switch. It was no seated properly and was allowing a vacuum leak along the top edge. I took it apart cleaned everything and reassembled and haven't had a problem since.
 

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ADMIN: feel free to move this if it's far off-topic.

Along the lines of HVAC control issues......while you have the dash apart, carefully inspect the connector at the motor speed control (I'm sure there's a better part description). I put in an NOS controller and shortly thereafter the motor would quit. A tap on the dash restored it. This kept on for quite a while until I decided to fix it. Upon pulling it apart, discovered the connector at the speed selector switch had become brittle and disintegrated. Looked like it might have gotten hot and semi-melted. It took out one of the power feed wires as well. Luckily I had a spare.

I'll post a pic.
 

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1984, 300 L6, smogless, manual 3speed with overdrive.
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Mine busted the plastic tabs on the inside of the heater box, the ones that hold the big baffle that switches from fresh to recirculate when the selectors are moved (opens and closes) so I pulled it out and duct taped it over the housing hole so now only gets fresh air
 
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