Pros And Cons Of Eliminating Blend Door Actuator

[friskyfrankie]

The Blend Door Actuator on my friend's 1995 Mercury Grand Marquis recently went bad. You can hear it clicking when first turning on the EATC and it gives codes of 024/025. Since he lives in South East Florida and has his heater core bypassed. we are considering removing the actuator and not replacing it. We all know the new one won't last very long anyway so I was wondering if this is a prudent move. We might be able to place the control rod permanently in the AC position and be done with it (if we can keep it there). Presently, even though the AC system is fine, the interior vent only gets down to 60 so it appears the blend door is partially open letting in hot air. Pros and Cons???

[sly]

I think the only pro is that the idea to lock the door in full cold since that's where it pretty much lives is a valid option. The problem is that the broken gears will allow it to move unless you just hot-snot the guts of the actuator. If you're going through the trouble to get in there to pull the actuator and glue it in position, might as well just swap a good one in. They're less than $30.

[friskyfrankie]

I think the only pro is that the idea to lock the door in full cold since that's where it pretty much lives is a valid option. The problem is that the broken gears will allow it to move unless you just hot-snot the guts of the actuator. If you're going through the trouble to get in there to pull the actuator and glue it in position, might as well just swap a good one in. They're less than $30.

Price isn't that much of an issue and I have seen OEM still available for under $50. It is more to remove the actuator completely to avoid having the need to do this same job again in the not too distant future! Was thinking of putting a metal shim under the "arm" to endure it stays in place.Have seen people putting erasers under the arm but that doesn't seem stable enough.

[gadget73]

just put a zip tie or mechanics wire in there. The arm has an L shape, loop a tie from the L to one of the mounting posts for the BDA to hold it in the full cold position.

[friskyfrankie]

just put a zip tie or mechanics wire in there. The arm has an L shape, loop a tie from the L to one of the mounting posts for the BDA to hold it in the full cold position.

Sounds like a winning idea!

[friskyfrankie]

From looking at videos, I wonder if you can get your hand/s in there, deep enough, to zip tie or wire up a solution?

[gadget73]

probably can see it but I dont think you can get your hands on it. the L bit is what the BDA sits on top of and I don't think there is any real space between the plenum box and the BDA to get anything in there. Can try it I suppose, maybe you can fish a piece of wire in there and get it to pull what you need.

[friskyfrankie]

probably can see it but I dont think you can get your hands on it. the L bit is what the BDA sits on top of and I don't think there is any real space between the plenum box and the BDA to get anything in there. Can try it I suppose, maybe you can fish a piece of wire in there and get it to pull what you need.

You are most probably correct. As previous stated, I was thinking of trying to put a small metal shim under the angle of the L bar to keep it in one position (A/C). Not sure if that would work, in reality, but that is the thought process. Move the L bar into the A/C position and then jamb the shim under it.

[kishy]

95 uses the newer EATC than the system I have vague familiarity with (e.g. 90-94) - but I think the operating principles are the same, just with a fancier control head.

I believe that the control head is aware of the location of the blend door actuator. e.g. not only is it chasing a temperature via the in-car temperature sensor, but it also knows the position and attempts to seek the desired position. I think that if the actuator were not permitted to move, this would cause the automatic fan speed function to not work correctly because the controls would be calling for the BDA to move before requesting the fan speed change. Maybe this is not bothersome though, and maybe it wouldn't even be a problem if the controls are only ever left at the very coldest setting.

Knock on wood here, but my '91, which uses the same BDA, has not eaten one yet and I've had the car since 2012. I'd probably keep one on the shelf - in fact, I actually do keep one on the shelf, and it's a Motorcraft - but I wouldn't pre-emptively disable the system. I would, however, and have, bypassed a heater core to reduce the amount of engine heat that even crosses the firewall to begin with. Sounds like that's already done though, which probably fixes the majority cause of BDA failure.

[friskyfrankie]

I actually changed it, on this car, but that was over 10 years ago and as I remember it, it was a "bear"! Not sure if simply removing it or replacing it is the best option as the fan speed issue, if accurate, would be a minor inconvenience. Guess I'll have to see what things look like as I approach it but with the current temps, that won't be happening soon! Just trying to see if we need to source the actuator or not.

[gadget73]

what I'd really love to know is why they fail in the first place. Not the gear that breaks, but why does it break. Does the controller try to push the BDA past the mechanical stop point of the blend door, and that stress is what causes it to crack? If so, why? There should be a position sensor in there that will tell the controller where its at, unless it does some self-calibration process and determines the end points based on when the value on the sensor stops changing, and that cal process stresses the parts to eventual failure. Bit of a shit design if thats whats happening.

A spring that would allow over-travel of the actuator would sort the stress issue, but would probably screw up the position calibration since the BDA would be able to over-travel by design.

[friskyfrankie]

what I'd really love to know is why they fail in the first place. Not the gear that breaks, but why does it break. Does the controller try to push the BDA past the mechanical stop point of the blend door, and that stress is what causes it to crack? If so, why? There should be a position sensor in there that will tell the controller where its at, unless it does some self-calibration process and determines the end points based on when the value on the sensor stops changing, and that cal process stresses the parts to eventual failure. Bit of a shit design if thats whats happening.

A spring that would allow over-travel of the actuator would sort the stress issue, but would probably screw up the position calibration since the BDA would be able to over-travel by design.

I think there is a group of sensors, under the gear that moves the arm that tells the EATC where the arm actually is. It may not, however, have a stop limiter, on either side. I always thought the gears or motor would be the fail points but never took a bad one apart to verify. Several Youtube videos seem to indicate that but I have no personal verification of that.

[gadget73]

it just sort of amazes me because the actuators in the Continental aren't that different. Same little weenie motor, plastic gear train, and a position sensor yet those are now 42 years old and still working. Its also a 15 minute job to swap, so you know that means it won't actually be problematic. Pull the glovebox door off and its right there. I've had the temperature and the fresh air / recirc motor out to lube since they were both sticky from sitting when I got it. The position sensor was dirty and causing strange issues too, one shot of contact cleaner and its like it never happened.

[friskyfrankie]

it just sort of amazes me because the actuators in the Continental aren't that different. Same little weenie motor, plastic gear train, and a position sensor yet those are now 42 years old and still working. Its also a 15 minute job to swap, so you know that means it won't actually be problematic. Pull the glovebox door off and its right there. I've had the temperature and the fresh air / recirc motor out to lube since they were both sticky from sitting when I got it. The position sensor was dirty and causing strange issues too, one shot of contact cleaner and its like it never happened.

Cool! The actuators on the CVs and GMs and same period TCs are buried pretty far in, as I remember (and also verified in various Youtube videos). Should be a "fun" project I am NOT looking forward to.