Troubleshooting Zone Control

By: Mike Holscher, Inside Sales Engineer at Jackson Systems, LLC

Although forced air zone control systems vary from one manufacturer to another, the principle of zoning is basically the same. A residential or light commercial zone control system uses multiple thermostats and motorized or pneumatic zone dampers along with a logic panel to control the air distribution from a single HVAC unit to individual zones. In most applications, a bypass damper is also incorporated to maintain the system static pressure as zone dampers open and close.

Typical Zoning System Layout

With proper test, check and start-up procedures, modern zone control systems require very little, if any, maintenance after the original installation. Unfortunately, not every system is thoroughly tested to assure that everything is functioning properly which usually leads to a user complaint after the fact.

If the service contractor is not the original installer of the zoning system, it is always a good practice to find out from the user what brand system requires troubleshooting as the original manufacturer can provide technical assistance, along with installation and operation manuals that will make the service technicians’ job a lot easier in diagnosing the problem. The zone thermostat on the wall is not necessarily the zone control brand. The user needs to confirm the manufacture of the logic panel which could be located on or near the HVAC unit, in a closet, garage or even in an attic. If they simply don’t know, or locating the panel is too inconvenient, then the technician is making a blind service call. This is where basic understanding of zone control systems can be a real plus in the troubleshooting process.

Before heading for the jobsite, the service technician should make sure to have the following in the tool kit:
Quality multi-meter
Digital thermometer
Small screwdriver that fits electronic terminal blocks
Flashlight
18-gauge thermostat jumper wires

Where to start:

Most user complaints come from not being comfortable. This could be related to multitude of things including zone thermostats, zone dampers, the logic panel or even the HVAC equipment. A good start is to find out if the problem is isolated to one zone or multiple zones. If it’s a single zone, the diagnostic process becomes less involved.  Typically a single zone problem can be traced back to a malfunctioning zone damper or zone thermostat.  Testing of the zone damper to see if it is opening and closing properly and replacing any defective parts on the zone damper can solve many problems.

Checking Zone Dampers for Proper Operation

Testing of the thermostat to see if it is operating normally by having it call for conditioned air would be the second troubleshooting step on single zone problems.  This can be accomplished by confirming that the zone control panel is receiving the correct corresponding signals from the thermostat. A jumper wire can come in handy here.  Disconnecting the thermostats from the logic panel and placing a jumper wire between the R terminal and the W terminal on one zone terminal can simulate a call for heat.  This can help confirm that the logic panel and the HVAC equipment are working properly.  Usually if a contractor can troubleshoot a thermostat that does not have zoning, they can troubleshoot a thermostat that does have zoning.
Multiple zone problems can be more complicated but the troubleshooting steps are similar to a single zone problem.  Isolating zone dampers and zone thermostats and testing each component individually should help you find the problem.
Troubleshooting the logic panel can more involved than troubleshooting individual zones.  The logic panel is where the thermostats, dampers and the HVAC equipment are tied together.

Trouble shooting Zone Panel

Testing the logic panel can be accomplished by using a quality multi-meter and checking for voltage or continuity at certain terminals on the panel.  If you are getting an input signal from the thermostat but you are not getting an output signal to the HVAC equipment the logic panel might need replaced.  Any and all fuses on the logic panel should also be checked to make sure they are in proper working condition.  It is best to have a separate dedicated transformer powering the logic panel in order to isolate the zone control system from the HVAC equipment.  Many logic panels have built in LED’s to help troubleshoot the zoning system.  These LED’s can tell the contractor when dampers are open or closed, when cooling or heating is being called for by the thermostat or when the fan is being called for.  The use of these LED’s can provide invaluable assistance in diagnosing zoning problems.
When testing any component, care is needed to make sure all wires are landed securely and that there is no break in any of the wiring.  If pneumatic tubes are used, make sure there are no leaks and the pump is functionally properly.
If the zone thermostats, zone dampers, and the logic panel seem to be in working order, then attention now needs to be focused on the HVAC equipment.  Disconnecting the R wire and the W wire from the logic panel and wiring these two together should bring on the equipment.  Testing of the HVAC equipment can follow the same testing procedures as if there was not zone control.  Sub-cooling, super-heat, temperature, and pressure readings should all be taken.
Forced air zone control technology has taken tremendous steps in the last decade.  Ease of installation, reliability of parts, and technical support from manufactures, are all areas that have improved that have allowed zone control to grow both in residential and light commercial markets.  Troubleshooting zone control systems is also an area that is seeing a higher level of expertise among contractors.  This expertise allows the end user to have a higher level of comfort than has been enjoyed in the past. 

Updated: October 23, 2008 — 5:00 am

2 Comments

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  1. I am the facitities manager here and we seem to be having problems in certain rooms being colder than others. I really think that the zones are working, but there are vents in the ceiling (drop ceiling) to allow the air to circulate. There is a lot of room between the drop ceiling and the flat roof decking (aprox. 15′ in some areas). Cold air seems to drop down through those vents like air conditioning in the winter months (now) even though the heat is on. I think the cold air is over powering the heat available. Are there standards for these vents and a possible solution? IE: Can these vents be closed off? this is a managed care home for the elderly.
    Jerry

  2. Jerry,
    You bring up a good point regrding static presure.
    An above ceiling open return should not drop cold air or any air for that matter into the occupied space through the return air registers as the supply air creates a natural positive pressure in the space that pushes the air into the return registers. The return air above the ceiling moves to the open return plenum. In a zoning application, a bypass damper is very important for above ceiling open returns as it maintains the proper static pressure so allowing the return air to enter the return plenum. If the bypass damper is not setup properly, there is a good chance that as zones close a positive pressure will build up above the ceiling thus forcing air out of the returns.
    I hope this helps.
    Mike Holscher
    Inside Sales Engineer

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