Latest from Residential HVAC

Photo 51372886 © Thinglass |

A Service Story

May 16, 2024

Troubleshooting Zone Control

Aug. 1, 2003
When it comes to troubleshooting, zoning is no more difficult than any other piece of HVAC equipment a service technician works on. Yet the perception

When it comes to troubleshooting, zoning is no more difficult than any other piece of HVAC equipment a service technician works on. Yet the perception among technicians is that zoning is much more difficult.

Many either fear to work on these systems or, because of a lack of knowledge or experience, assume that any airflow problem in a building that is zoned is directly linked to the zoning system.

In reality, a zone control system can be easily diagnosed and repaired if the service technician has the proper training and follows a set of procedures. Here is a general process list to help you troubleshoot a zone control system.

Is It Really The Panel?

The first step in a situation where not enough or no air is being introduced into the living space is to make sure the standard mechanical equipment is working properly. That includes checking refrigerant levels, filters, etc. If everything is as it should be and the mechanical system is operating as it should be if airflow is still too low, then begin examining the zone control system. Use this procedure:

  1. Using a voltmeter, verify that there is panel input control voltage. The voltage reading should be between 10% of 24 VAC (22 to 27 VAC).
  2. If there is power, then verify the PC board internal voltage supply. This should indicate the voltage as required by the specific manufacturer of the panel. If not, you need to replace the board.
  3. If there is power, test the output relays (which control the equipment hooked up in each zone). If the HVAC output LEDs indicate a call for equipment, and the equipment doesn’t respond, the relays should be tested. Testing can be done using one of three methods: jumpering (from R-W, R-G, R-Y), voltage test (W-C, G-C, Y-C), or ohms test (R-W, R-G, R-Y) with wires removed.
  4. Check for proper function switch positions. You need to understand the importance of each switch position on the board and how that relates to the equipment being controlled. On-board functions switches must be set for desired results. If you make any switch changes, you might need to restart the board by turning the power switch off, then back on.
  5. Before accusing the panel for the problem, make sure the thermostats are sending the proper signal. Do this checking for 24 volts from the “calling” terminal to “C”. If there is no 24V signal from the thermostat, jumpering out the thermostat at the subbase will prove whether the problem is with the thermostat itself, or a wiring problem.

    If you jumper out the thermostat at the subbase and the zone works, then you have a thermostat problem. If the zone doesn’t work, there’s a wiring problem.

    Some power-robbing thermostats will illuminate one or two LEDs without an actual call. So be sure to check for 24V to “C”.
  6. Check all wiring (or airline) connections to dampers and thermostats.
  7. Conduct a damper operation test by hot-wiring the dampers to make sure they work. Test for voltage, pressure, and vacuum at the zone damper terminals. On electro-mechanical types, you need to check for stripped gears, damper motor failure, and so on.
  8. Conduct a leaving air temperature sensor and circuit test. Be aware that an improperly set leaving air temperature (LAT) control will cause nuisance short cycling of equipment. Set the LAT to allow a long enough cycle needed to satisfy the zone calling. If the bypass is sized properly, the extra cfm will help to satisfy a single zone call more quickly.

    The proper LAT setting should be no more that 70F above the manufacturers’ maximum temperature rise. The cooling leaving air temperature setting should be between 40 and 48F. Oversized and/or improperly adjusted bypass controls will cause equipment short cycling.

    Leaving air temperature set points must be outside the normal range for a zoned HVAC system. Remember, excessive bypassing will cause extreme temperature issues at the equipment.
  9. Conduct a bypass test. Bypass need is determined by air noise at the registers. Bypassed air has a negative affect on the airflow (cfm) requirements of the equipment. Return airflow is directly proportional to supply air delivered to the space. Every bypass must be adjusted per the individual application.

    Adjust the bypass to open only when the smallest zone has objectionable air noise.

    If you follow these tips, troubleshooting zone control systems should be no more difficult than troubleshooting the refrigerant system or any other part of the comfort system.

    But if you do run into a problem that you can’t figure out, call the manufacturer for technical assistance. When possible, make that call while on the jobsite so the manufacturer can walk through the problem with you real-time.
  10. One last tip: most manufacturers have troubleshooting guides for their contractor customers. Check out their websites or call them and request a copy.

Joe Ramunni is the technical sales manager for Arzel Zoning Technology, Inc., Cleveland, OH. Ramunni has been in the HVAC industry since 1974, working for a Northeastern Ohio contracting firm as a service technician and later as the service manager. He can be reached at 216/831-6068 or at [email protected].