How to bi-pass low-n-high? '86 MGM Tudor

[Toploader]

TBL by-passed and ports were plugged.

I would check out the vac lines going to the TBL. That's what the problem was on Bobby's GM!

[Toploader]

Gadget, yes all of a sudden the blower motor stops blowing, or the air flow out of the dash vents is so tiny it is just like the blower stopped. The blower resister plug is good, as is the motor itself....used Caig products pro gold to clean the connects....all were good! Per your suggestion last year, I removed the TBL from the heater hose, and plugged the ends....now the heater will work on demand with no waiting till the water heats up. Since I do have an NOS dash board blower switch, I will replace that, or am I waisting my time? Btw, this blower motor slow down happens in all positions...floor, bi-level, or dash vent! I thought this would be an easy plug-n-play fix situation, as I also remember you suggesting I change the coffee can, but, as I mentioned, when the shop applied vac to it with that hand pump, the can held vac and did not leak down.

If its cutting in and out completely, thats a different problem. Sounds like electrical gremlins somewhere in there. If the blower motor resistor plug is shaky, that might explain it. The connections at the blower itself also get bad. Its a high current circuit, anything remotely questionable will cause problems. If you're hearing the motor go silent entirely, look at the electrical stuff first.

The TBL is only a factor if it does this in "floor" mode. That switch is not in play in any other mode. The vacuum section does cause leaks that shift things towards hot and to the defrost vent, but they won't kill the blower motor.

Small airflow changes are probably fresh air / recirc door action related. You can't manually force operation of that on an ATC system. When the blend door is at it's extreme, its in recirc, so the air door under the dashboard opens and pulls air from inside the car. If it moves just a twitch, that shuts and you get air coming from outside. Due to the way the air ducts are shaped, and because you're trying to shove air into what is essentially a sealed (albeit poorly) passenger compartment, its going to move less air than when its just moving the air in a circle. On the manual climate control, simply moving the selector from "max AC" to "normal" or whatever its marked as will control that door, and you'll likely notice the same sort of minor airflow changes. There is a definite noise level change there too, its louder in recirc (max) mode.

[sly]

at this point, I'd check the vacuum feed line to the AC controls to see if it's plugged or kinked. Replacing that line is a bitch and a half, but is sometimes needed. All you need to do to test it is disconnect the vacuum harness either at the controls on the intermediate harness that might be hanging down by the vent actuators. Disconnect the skinny lines from the check valve under the hood at the firewall vacuum tree as well. This should leave it open at both ends. try to pull a vacuum on the black line from the vacuum harness under the dash. If you can actually pull ANY vacuum, replace the line through the firewall. It's probably kinked as it comes over the air plenum and drops down into the dash.

[lincolnlarry]

But why does it return to high blower after like 30 seconds?...

I would say a bad connection to ground. Like gadget said I would ground the blower directly under the hood. Whenever the heat/ac is on it will have no choice but to run in high.

[Toploader]

Before breaking things...................can someone advise step by step instructions to remove and replace the blower motor switch on the dash?

I attempted to reach under the ash tray to feel the switch, which I was not able to do.

Thanks for the help!!

[lincolnlarry]

Once you remove the dash trim around the controls you can get at the screws holding the controls in.

[Toploader]

LOL..........and how do I effectuate such removal????????????

Once you remove the dash trim around the controls you can get at the screws holding the controls in.

[gadget73]

I don't own a Ferd, so this is recollection of fuzzy memory from one time I did this some years back. Hopefully someone that has had one apart more recently than years ago can assist here but I think its just 2 screws in the ash tray area and then the panel around the climate controls just pulls out. Once that panel is off, you'll see 2 or 4 screws holding the climate control panel in. Pull those and the climate control unit pulls out. Once thats in your hand, I believe its just 2 screws in the back side that hold the switch in place.

[Toploader]

Ok I found the step by step procedure in the 1986 shop manual.

Thanks gents!!

[gadget73]

Cool. I don't remember it being particularly difficult, just don't quite remember the specifics of it.

[Toploader]

The last thing I want to do to rip into the dash and the rats nest of hoses etc........if replacing the switch cures this, I will be a happy camper

Cool. I don't remember it being particularly difficult, just don't quite remember the specifics of it.

[sly]

just for good measure, I'd double check those connectors on the stuff you've replaced already. I've had issues with the new blower connector coming loose a couple of times on my 88. Sometimes a zip-tie will work wonders for keeping things together.

[Toploader]

Ok so today I installed the new blower switch and cleaned the connector.......followed the steps in the shop manual and had no problem.......I will see if the blower continues to just stop and then start...........if it does, then I will trace the ground(s) and re-do.

[lincolnlarry]

This has me very interested. And yes, the grounding point for the switch that makes the blower run high is separate from the ground point the blower resistor uses for the default low speed. I call low speed the default because when the blower switch is removed the fan will still run in low. I think the switch grounds under the dash but I'm not sure whereon your car. An 87 LTC has the switch grounded to a brace in the center of the dash.

[Toploader]

Larry my '86 MGM Tudor also has the switch grounded to a brace in the center of the dash.......I found the location in the Emissions/Electrical soft covered FoMoCo manual. I was super careful, as the center wood grained plastic cover plate is indeed delicate.

This has me very interested. And yes, the grounding point for the switch that makes the blower run high is separate from the ground point the blower resistor uses for the default low speed. I call low speed the default because when the blower switch is removed the fan will still run in low. I think the switch grounds under the dash but I'm not sure whereon your car. An 87 LTC has the switch grounded to a brace in the center of the dash.