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Central AC - Damper Sometimes Won't Open...Why?

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Hoping someone here can point me in the right direction. Here's what I have and what's happened. Central AC unit with 2 zones for my upstairs (one zone has bathroom, laundry room, 2 bedrooms while other zone has playroom and 2 bedrooms.) The zone for the playroom/2 bedrooms all of a sudden just stopped working. Thermostat set at 73 but was reading 82 (this started in July.) I went into the attic and realized that air was on but the damper was closed. I manually opened the damper and it was fine. This repeated itself randomly until I stopped using the AC this fall. Sometimes it would work fine for 3 or 4 days and then just not open again. The other damper worked completely fine all the time. I had my HVAC company come up and look and they kind of looked at me sideways and told me to change the thermostat for that zone. It was the only solution they offered while sending me a bill for $125 for their time spent. I did that but it didn't solve the problem. 

 

I'd like to try get out in front of this over the winter if possible. Any ideas on what could be wrong?

 

Thanks all!

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So you're having an intermittent issue with just the damper? This is a motor controlled damper? I can't say what it is but as far as diagnosing, start at the source and work backwards. If the damper is operating ok, then move to the board or relay or whatever sending power to the motor. The actuator motors that I work on have switches on them that tell the unit where it's positioned, so to speak. If the switch failed and the motor can't find "home" they will not work. 

 

Again, not sure about your situation and HVAC isn't really my game. 

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Check the motherboard there are relays that take the heavy loads, little back boxes that look like the ones you have in your car fuse box but a little smaller, most motherboards are tan look around the relays to see if there is any discoloring like it overheated around the relay   

area, most likely you have a bad solder connection on the relay pins that will give you an intermittent problem. 

At work, we had 15 units all the same for AC & Heat they were 15 years old, and all of a sudden one by one either no heat or ac tap the control box and it would start, called for service says bad motherboard $500 installed for a new one and its up and running, l kept the old Honeywell board took it to the machine shop looked at the discolored area at the relay and there was the problem cold solder joints l resolder the relay pins then l changed out the motherboard in the machine shop unit and it's working fine intermittent start gone.

 

Something to look at motherboards are not cheap. if your handy it's an easy fix.

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On 12/9/2022 at 7:46 AM, Scallywag said:

So you're having an intermittent issue with just the damper? This is a motor controlled damper? I can't say what it is but as far as diagnosing, start at the source and work backwards. If the damper is operating ok, then move to the board or relay or whatever sending power to the motor. The actuator motors that I work on have switches on them that tell the unit where it's positioned, so to speak. If the switch failed and the motor can't find "home" they will not work. 

 

Again, not sure about your situation and HVAC isn't really my game. 

Thanks for taking the first stab at this!

On 12/9/2022 at 8:59 AM, LB said:

Check the motherboard there are relays that take the heavy loads, little back boxes that look like the ones you have in your car fuse box but a little smaller, most motherboards are tan look around the relays to see if there is any discoloring like it overheated around the relay   

area, most likely you have a bad solder connection on the relay pins that will give you an intermittent problem. 

At work, we had 15 units all the same for AC & Heat they were 15 years old, and all of a sudden one by one either no heat or ac tap the control box and it would start, called for service says bad motherboard $500 installed for a new one and its up and running, l kept the old Honeywell board took it to the machine shop looked at the discolored area at the relay and there was the problem cold solder joints l resolder the relay pins then l changed out the motherboard in the machine shop unit and it's working fine intermittent start gone.

 

Something to look at motherboards are not cheap. if your handy it's an easy fix.

LB, thank you! Sounds like this could be the problem and the solution. I'm not handy but know enough people that are to hopefully diagnose and fix the problem. I'll start here....Thanks!

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First thing to determine is if it is a power open or power close damper. Most residential systems used a power close damper so when that zone is not calling the motor closes and holds it closed. On a call for heat or cool the motor is de energized and damper springs open. It could just be a burr or rough spot not letting damper open when de energized.

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