Troubleshooting and fixing a fresh air supply damper that's not working. :

This article series explains manual and automatic heating and air conditioning or ventilatino ductwork zone dampers & airflow controls.

Stuck Fresh Air Damper Control

Reader question: 6/30/2014 Michael said: How common is it for a damper to get stuck?

I disconnected it from the motor controller and I noticed the rod that adjusts the damper was not moving.. and when I forced it to move the rod to open it just now spins in a 360.. but I never heard the dampers open..

it's a Trane H&V system from the early 60's

Reply:

Michael I have not found statistics on damper failure, and I pose that the failure in "stuck" mode would vary widely by damper type. Most often a motorized damper failure to open or shut is probably a motor or control failure.

Watch out: Forcing a damper to move if the motor is jammed might break the drive shaft or gears, leaving the damper flopping freely but no longer under motor (or manual control arm) control.

That's a particular risk if the zone damper actuator (motor) uses a plastic or nylon actuator gear.

At this point I'd take a closer look at the control, motor, and connections by removing and inspecting the assembly.

Let me know what you find, or use our CONTACT link to send me some photos and I can comment further.

Reader follow-up:

Hi I sent the email, the motor damper is fine but someone that opens and close the dampers have bound up and so the dampers are closed.

So here is the story I noticed the arm for the damper from the motor control was not locked down on the rod for the damper, so for testing I disconnected the rod and tried to manually turn the damper by hand and I noticed the damper would not move in ether direction.

I tried to get the damper to move by using some pliers by turning it clockwise and all the rod does now is just spin in circles, and I never heard the dampers move at all.

I was trying to get the damper to open because the church at night is 86 F inside and under 67F at night so cooler air inside would be nice.

Reply: stuck fresh air damper vs zone damper: same repair procedure

Inside the ductwork the damper typically combines a flat metallic blade shaped to match the cross section of the duct work with a rod that is fixed to the center of the blade. Your photo shows the end of that operating rod.

Corrosion, a bent damper blade, or loss of connection of the damper blade to the rod can leave the damper stuck and the rod spinning freely.

Since the problem is not that the damper motor is broken but rather that the damper itself doesn't seem to move, the repair is most likely going to require opening the ductwork and repairing or replacing the damper assembly.

Your damper and grille are not a zone damper (which opens or closes hot or cool air to a building area) but rather a motorized damper that controls the admission of outdoor air into a building's HVAC system.

This is a VENTILATION, SUPPLY-ONLY system design.

However the damper operating principles are the same except that outdoor or makeup air supply dampers are often controlled not by a thermostat and motor but by a manual cable or lever that allows the HVAC technician to leave the fresh air supply damper in a set position.

Reader follow-up:

Thank you Daniel for adding the info to help others as the church does not have A/C right now and only 200A 120/208V service we are having a issue finding if the church is able to have A/C the issue is the amount of people square feet and A/C tons needed.

The size of the area that needs cooling the most is 4,153 sq. ft with a 27' high ceiling and 400 people.
I can provide a photo of the area, it's pretty much split into 3 blower units and I can't find any info on the trane units at all.

Reply:

Mike, At BTU CHART for AIR CONDITIONERS / HEAT PUMPS

you'll see a BTU sizing chart, though it does not go up to 4200 sq ft. - you can extrapolate.

But a more intelligent design for a large space with a high ceiling takes more into consideration:

- the ceiling height (as you know)

- the distribution of locations of both supply air and return air ducting and its sizing

- the requirement for variation in cooling depending on occupancy level (more people during holidays for example)

- CFM cubic feet per minute movement by one or multiple (staged) air handlers

- introduction of makeup air is also an interesting topic. I measured the CO2 level at a New York synagogue during services and found that the CO2 level climbed steadily over the period of religious services (which may have explained people dozing during the Rabbi's sermon).

The building had no fresh air introduction system at all.

Typical rules of thumb for fresh air ventilation in buildings require

15 CFM per person OR 0.15 CFM/sq ft

Where mechanical ventilation rather than passive (windows) venting is required, the total ventilation air flow rate requirement is estimated by

CFM - cubic feet per minute of air movement = Room volume (in cubic feet) x (Number of air changes per hour required) / 60

As you've already learned by the stuck damper, motorized dampers need to be inspected & maintained - very often I enter a large building where the building super thinks the heating & cooling are working just fine only to discover by entering spaces where no on has been for some time that the system has been snarled up for years.

I find disconnected air ducts cooling the attic instead of the occupied space, jammed dampers, even air handlers that are simply not running.

A thoughtful design will inspect the whole building, discuss its occupancy schedule and level, and will evaluate the insulation, windows in number and type, air leakage, and might even perform a blower door test.

The more accurately you understand the building's heat gain in hot weather and heat loss in cold weather the more effective and economical can be the HVAC design.

I infer from our correspondence that there was an automated or manually-set fresh air introduction system - though it may have been only for heating.

You will want to know the details about the equipment already installed: location, capacity, economy, features as well as to consider add-on or retrofit vs other cooling options (rooftop or outdoor split system units might be adequate and less costly)

An "Economizer" uses outdoor air ventilation to cool the indoor space at lower cost than using a refrigeration-operated system and works when outdoor air is at or below 72F.

...

Continue reading at ZONE DAMPER ACTUATOR MOTOR REPLACEMENT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see ZONE DAMPER REPAIR FAQs - questions & answers posted originally on this page, for help diagnosing problems with manual or automatic air duct zone dampers & damper controls

Or see these

Recommended Articles

• DAMPERS & DRAFT REGULATOR TYPES
• DUCT SYSTEM DESIGN SIZE & DEFECTS - home
• FIRE & SMOKE DAMPERS, AUTOMATIC
• VENTILATION in BUILDINGS - home
  • BALANCED VENTILATION, HEAT COST SAVINGS
  • FRESH AIR DAMPER CONTROL REPAIR
  • FRESH AIR VENTILATION RATES & STANDARDS
  • VENTILATION, BALANCED
  • VENTILATION DESIGN PROBLEMS & SOLUTIONS
  • VENTILATION, EXHAUST ONLY
  • VENTILATION, SUPPLY-ONLY
  • VENTILATION, WHOLE HOUSE STRATEGIES
• ZONE DAMPER CONTROLS
• ZONE DAMPER ACTUATOR MOTOR REPLACEMENT

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FRESH AIR DAMPER CONTROL REPAIR at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC DUCT SYSTEMS

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