It’s a cold morning in Huntsville. The thermostat says Heat, but the air from your vents feels cool. Some causes are simple to check yourself. Others need a technician. Here is how to tell the difference.
1. The thermostat is set wrong
Make sure it is set to Heat, not Cool or Off, and that the set temperature is a few degrees above the room temperature. If your thermostat uses batteries, replace them. A blank or flickering screen is a common cause of a “no heat” call.
2. The heat pump is in defrost mode (this one is normal)
In cold, damp weather, frost builds up on the outdoor coil. Every so often the heat pump reverses for a few minutes to melt it off. During defrost you may see steam rising from the outdoor unit, hear a whoosh, and feel cooler air at the vents. A defrost cycle usually ends within about 10 minutes. On many systems the backup heat strips come on during defrost to keep the air warm.
3. The outdoor unit is covered in ice
A light frost that comes and goes is normal. A thick layer of ice that covers the coil and does not clear after a defrost cycle is not. Common causes are a failed defrost sensor or control board, low refrigerant, or an outdoor fan that is not running. If your thermostat has an Emergency Heat setting, switch to it and give us a call. Please do not chip the ice off. It is easy to puncture the coil.
4. The air filter is dirty
A clogged filter cuts airflow. The system runs longer, the air feels lukewarm, and parts work harder than they should. Pull the filter and replace it if it looks gray. Most homes need a new filter every 1 to 3 months.
5. A breaker has tripped
A heat pump has an outdoor unit and an indoor air handler, and each one has its own breaker. The backup heat strips often have one too. If one trips, you may get a fan blowing with no heat, or heat that never gets very warm. Reset a tripped breaker once. If it trips again, leave it off and call us. A breaker that keeps tripping points to an electrical problem.
6. Refrigerant is low because of a leak
A heat pump moves heat with refrigerant. If a leak lets the charge get low, the system cannot move enough heat, and the outdoor coil may ice up. Refrigerant does not get used up, so low refrigerant always means a leak. The right fix is to find and repair the leak, not just add more.
7. A part has failed
Capacitors, contactors, the reversing valve and the outdoor fan motor all wear out over time. Signs include an outdoor unit that hums but will not start, a fan that does not spin, or a system that heats on some cycles and blows cool on others. These are repairs for a licensed technician.
Why your heat pump runs longer when it is cold
A heat pump pulls heat out of the outdoor air. The colder it gets, the less heat there is to move, so the system runs longer cycles. That is normal. On the coldest nights the backup heat strips help out. If your system runs nonstop and the house still will not reach the temperature you set, have it checked.
One more note: the first time the backup heat runs each fall, you may notice a dusty smell for a few minutes. That is dust burning off the heat strips and is normal. A strong burning smell that does not go away is not. Turn the system off and call.
When to call North Alabama Heating & A/C
- Thick ice on the outdoor unit that does not clear
- A breaker that trips again after you reset it
- A burning smell that does not go away, or grinding or banging noises
- Cool air at the vents for more than 15 to 20 minutes at a time
- A house that will not reach the temperature you set
We have repaired heat pumps in Huntsville, Madison and across North Alabama since 1977. Call (256) 534-2941 or learn more about our heat pump repair service.
