After some research and realizing why we are receiving so many service calls on “No Heat” or “System is blowing cool air” and why most of these calls come in early morning or late nights, I have discovered the process of how the heat pump works:
When the outdoor temperature drops below 42 degrees in the valley, frost can build up on the outdoor coil of your heat pump. The defrost cycle helps eliminate any accumulated frost. While the cycle runs, residents can briefly feel cool air coming from the vents.
While every manufacturer is different, many heating systems are designed to go into a defrost cycle every 30, 60 or 90 minutes if the outdoor air temperature remains below a certain level, in most cases 40 degrees. It's important for the resident to understand that, on cold days, their home is not running the air conditioner to cool the house. Systems are designed to effectively balance the cool air with hot air so that the home doesn't get too cold.
What to look for
- Noise, cold air: A loud, hard-working condenser and swishing sounds in the refrigeration lines are usually part of the defrost cycle experience. And yes, as a result of the system working so hard to heat those outdoor coils, you're indoor vents are blowing cooler air for a short time.
- Water run off: Some units may even see water dripping or steam rising from the outdoor condenser coils. Customers with rooftop units often become concerned when the ice defrosts and the water runs down the roof. But that's actually a sign that the system is operating correctly during the defrost cycle.
- It's temporary: A defrost cycle can last up to 20 minutes. DO NOT TURN OFF THE TERMOSTAT, as it can delay the cycle. It's normal for the thermostat to drop a few degrees during the process, too.
- Red flag: Check the outdoor coil. If you see frost accumulated on the coil that does not go away, then you will need a visit from an HVAC expert.
- One temperature rule: Keep in mind that a system runs best with the thermostat set at one temperature, recommended between 69 and 72 degrees. "Set it and forget it!"
Specific questions that can help the technician understand if they are dealing with a defrost issue or something more serious include:
- At what time did the system begin blowing cold air?
- Do you remember the approximate outdoor temperature when the system seemed to be malfunctioning?
- Have you changed your thermostat setting or turned off the system recently?
