A Technician’s Advice for Weathering Winter

When the weather outside gets frightful in select portions of the U.S., operators just might be in for disruption indoors, as well. For some insight on potentially sidestepping downtime and added costs, we checked in with Jason Williams, Delaware Valley field service supervisor at Baltimore-based EMR.

FER: What are the main wintertime equipment issues you see in the mid-Atlantic?

Jason Williams: Once we get the first cold snap of the year, we tend to see more issues with refrigeration equipment than with cooking equipment. Common problems include frozen drain lines and fan motors failing due to cold stress. We also see headmaster valves sticking and fan-cycling controls failing.

With commercial HVAC equipment, we often encounter flame sensors failing because of oxidation buildup from being outdoors year-round. Gas valves and inducer motors can fail in the cold as well. Heat exchangers also tend to rust out. During the summer, the cold air from the AC blows over the heat exchangers and creates condensation; over time this leads to rust pits. When we perform heat startups in the winter, these issues show up, requiring heat exchanger replacement. If left unaddressed, they can cause high-limit trips, rollout switch trips and, most importantly, high carbon monoxide levels from incomplete combustion.

FER: Walk me through a service call for these issues; what will an operator notice first?

JW: One of the issues we commonly see this time of year is failed headmaster valves, and they can be tricky to diagnose. Headmaster valves are designed for refrigeration equipment that operates in low-ambient conditions, such as rooftop condensing units used during cold weather. They act as metering devices that take hot gas from the discharge line and bypass the condenser, sending it directly to the receiver to raise head pressure so the system can run properly in cold temperatures.

One scenario we encounter is when the valve is stuck open, causing the system to trip on high head pressure. We can feel the line coming out of the valve and going into the receiver. If it’s very hot that means hot gas is being fed into the receiver and raising the head pressure and tripping the high-pressure switch.

Another scenario is when the valve is stuck closed. This makes the system look like it’s low on refrigerant because the condenser pressure will be too low, and you’ll see bubbles in the sight glass. We can block off the condenser to raise the head pressure and see if the valve returns to normal operation. If the pressure rises quickly, we know it’s not a refrigerant charge issue. In some cases, we can snap off the capillary tube on top of the headmaster valve to release pressure, which can temporarily get the system running again. However, this is only a temporary fix since the valve will need to be replaced, or a fan cycling control will need to be installed.

FER: What is the typical fix and cost for the issue(s)?

JW: Usually, replacing the valve is more costly than installing a fan cycling control. However, it’s generally better to replace the valve so the system can operate as it was designed. Replacing the valve can cost a couple thousand dollars, while installing a fan cycling control might only cost a few hundred dollars.

FER: Besides planned maintenance, what’s an operator’s best bet for avoiding these wintertime issues?

JW: Preventive maintenance is always the best way to avoid most issues, but sometimes these parts fail without warning. Performing
regular maintenance tasks like cleaning condenser coils, verifying proper refrigerant charge, inspecting heat exchangers, cleaning flame sensors and ignitors, checking and cleaning inducer motors, and inspecting and replacing belts as needed will always serve as your first line of defense.

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For more maintenance advice, including a recent article on how to get a first-time fix, click here.