Troubleshooting Pneumatic Zoning Systems

Troubleshooting residential pneumatic zoning systems is usually a simple matter of using the process of elimination. As with most things we encounter in our work, problems with pneumatic zoning systems can be electrical or mechanical, or can be related to the air pressure and vacuum that is used to open and close the system’s dampers.

Many technicians — especially those who have not had much experience with zoning systems — are intimidated by the control panel. There are lots of wires and lots of terminal strips, especially in systems that have three or more zones. The key piece of advice here is to isolate the system components. Mentally break the system down into two sections. One is between the thermostats and the zone control panel, while the other is between the zone control panel and the equipment. When diagnosing between the control panel and thermostats, think of the control panel as the furnace. Each zone has its own terminal strip, just like a furnace circuit board. When diagnosing between the control panel and the equipment, think of the control panel as a thermostat. Its output terminals are like the terminals on any of today’s sophisticated multi-stage thermostats.

Let’s say you receive a complaint about a zone not responding to a request for heating and cooling. After listening to and understanding the homeowner’s specific information about the problem, the first step you want to perform is to be sure the thermostat for that zone is calling. Troubleshoot that as you would any system, but remember to think of the zone control panel as the furnace in the system.

Are the other zones working? If yes, does the problem zone pass the electrical tests you did in the prior step? If no, isolate the electrical problem to the thermostat, connecting wires, or the control panel. Here, the same rules apply as for all circuit boards: if there is power in but no power out, the problem is in the board.

If all electrical tests pass, the problem must be in the mechanical or pneumatic side. Disconnect the main air tube for the problem zone at the panel. Use your mouth to create vacuum or pressure and see if the dampers open or close. They suck open and blow closed. If the dampers work, look at the control panel and pump. If the dampers don’t work, look to be sure all tubing is secure with no kinks or other obstructions and no leaks. If the problem persists, check one damper at a time using the same method. If a damper doesn’t work, is it binding on the duct and being kept from opening and closing? If it’s not binding and won’t respond to your “mouth test”, the actuator is bad. It’s very unlikely that all dampers would do this, so double check your diagnosis.

Bill Campbell is president of Campbell Comfort Systems Inc., Woodbury, NJ. He can be reached at 856/845 2100 or by email at [email protected]

Round Up the Usual Suspects to Assist You in Your Troubleshooting


Like any diagnostic process, the majority of the battle with pneumatic zoning systems is to get the patients to properly describe the symptoms they are experiencing. Figuring out zoning problems is not much different.

When homeowners who have been used to feeling the comfort of specifically controlled airflow are suddenly uncomfortable they recognize it quickly, but in many instances they don’t know what the cause of the discomfort might be. Round up and examine all of the usual suspects. The lineup should look like this:

  • Thermostat function
  • Power to the control board
  • Identification of the specific zones and duct runs in question
  • Inspection of any mechanical balancing dampers
  • Observation of damper activity

These steps are general to any zoning system. In the case of an air-driven damper system we add a couple line items:

  • Is the air source (pump or compressor) powering up and delivering pressure?
  • Is the integrity of the airline tubing complete?
  • Does the damper hold pressure?

There are few real differences in the base concept of dampers. Air-actuated dampers utilize a diaphragm to move the vane in the duct to match the service requirement, instead of engaging a motor and gear mechanism.

The tools required for this testing are very basic. In residential air-driven systems you are dealing with minimal pressures, (2-3 psi) at the maximum. No sophisticated gauges are required. Testing the integrity of a damper is easy. Simply cover the air intake with your finger and move the blade; if you do not have resistance, you have a bad damper. If you need to test the air source, a basic digital manometer will quickly diagnose a line problem from a pump deficiency.

Air line leaks can be caused by a rodent chewing on the tube or a dislodged connection. They can also be pinched just the same as a pinched wire can be broken on an electro-mechanical damper. If the airline is compromised, simply install a coupling at the leak and reconnect the line. Air lines are easily attached and most are color-coded by zone.

Dennis Laughlin is president of Arzel Zoning Systems, Cleveland, OH. He can be reached at 216/831-6068 or by email at [email protected]

TAGS: Controls
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