When designed and installed properly, modern residential zoning systems are generally very reliable. They serve to provide even heating and cooling throughout a home and eliminate hot and cold spots. By their very nature, they help ensure that a home's HVAC system is well-balanced.

However, like any mechanical device, zoning systems may occasionally present challenges to a service technician. Here are some things to remember when you arrive on a service call and find that the homeowner's HVAC system includes a zoning system.

Know the Features.
First of all, there are a number of different zoning systems on the market, so it's important that you familiarize yourself with the sequence of operation of the system you've been called on to diagnose. Each manufacturer's system works a little bit differently, and knowing how a system is designed to operate is the first step to effective troubleshooting.

As zoning systems are inherently self-balancing, a service call will usually be prompted by a comfort complaint: the homeowner notices that a certain room or area of the house is overheating or underheating, or over- or under-cooling.

In such cases, the number one culprit is an inoperative damper or a thermostat that's out of calibration. So, the first place to start is to check dampers for proper operation, and thermostats for proper calibration.

First Steps.
The initial diagnostics are pretty much common sense: take a walk through the house and check airflow at the registers. This initial check will tell you if the system is over-conditioning an area (which likely means a damper is stuck in the open position) or not providing any heating or cooling (which likely means a damper’s stuck closed).

In most modern zoning systems, you can either look at the dampers or the zoning panel to determine what position each damper is in. Some dampers even have a light that indicates the damper's position.

Although zoning systems are usually very reliable, outside influences — such as duct cleaners or cable TV installers who may try to run a cable through a duct — can affect them in a negative way.

If the zoning panel doesn't indicate damper position, it's fairly easy to check the dampers themselves — if you can physically access the dampers. On all of our zoning system installations we're careful to make sure we're using the proper dampers for the application. Whether they're side-mount, bottom mount, etc., we position them so we can easily see if they’re open or closed. This aids in troubleshooting, and ensures clear access to dampers in cases where they must be replaced.

Expect a Few Surprises.
Unfortunately, dampers sometimes get "buried." It happens rarely, but we've seen cases where homeowners have drywalled over top of them, usually when they're finishing a basement. When you run into something like this, you just have to do your best to locate the hidden dampers, and remember that challenges like that is what keeps HVAC service work interesting and rewarding.

Be aware that although zoning systems are usually very reliable, outside influences — such as duct cleaners or cable TV installers who may try to run a cable through a duct — can affect them in a negative way. When you're called to check on a zoning system that seems out of balance, ask the homeowners if they have had any work done recently that may have affected the operation of their zoning system. What they tell you can help provide important clues for your diagnosis.

It's unusual for problems at the furnace or air conditioning compressor to cause problems with a zoning system, but be aware that zoning system malfunctions can cause woes for the units.

For example, if a damper is stuck closed it could cause an air conditioning condenser to ice up, or a furnace to overheat and shut down on a limit control. Although most zoning systems have built-in limit controls that will cycle a furnace off if it reaches a high temperature limit, not all of them do. If you’re working with a zoning system that doesn't have a high limit feature, you could have a furnace that's cycling off of a limit, which in turn could ultimately cause the furnace to lock out, or the limit to fail.

This would present a different service call — a no heat call — rather than a comfort problem in a specific room or rooms. A customer would call you with a furnace that’s cutting off, but the problem may be caused by the zoning system rather than the unit.

When you arrived at the no-heat call, you would likely concentrate on getting the furnace up and running. When you discovered that the limit was tripped on the furnace, you would start to look for the cause. Typical causes can be a dirty filter or a plugged evaporator coil. After you've checked those, be sure to consider that restricted airflow caused by a closed damper could be a complicating factor.

It Starts with the Sale.
Finally, remember that zoning system service starts with zoning system sales and installations. When you're on service calls and customers complain about certain rooms being too hot or too cold, be sure you educate them about the benefits of zoning. Many service technicians aren't comfortable being a "high pressure salesperson," but there's no need to be. Simply provide a little education about how there is a reliable solution that could provide them with even, balanced comfort throughout their home.

Greg Smith is president and Rich Haga is service manager of Quality Heating and Sheet Metal Company, Brookfield, WI. Smith can be reached at 262/786-4450, or by e-mail at gsmith@qualityheating.com.