About a month ago, we received a call from one of our heat pump customers. She reported that the multi-head ductless system we had installed last November had heated well all winter but when she switched to air conditioning, she noticed a problem. Her husband’s office, on the top floor of their split-level home, wasn’t staying cool. Their bedroom suite, a floor below, was uncomfortably cold.
The technician we first sent to troubleshoot turned on the heads, both nominal 9000 Btu/h high-wall units. The heads responded as expected to the handheld remote controller and started blowing cool air. After performing a quick visual check, the tech reported that the system appeared to operate as it should.
A few weeks later, the customer called back with the same complaint. This time I decided to run the call myself to see if I could figure out what was going on. Troubleshooting ductless temperature control issues has become a passion of mine, and I wanted to get to the bottom of this situation.
Possible reasons for unexpected temperatures
As I drove to the house, I ran through a list of possible causes for the inadequate cooling in the study. Dirty filters could be reducing airflow; a refrigerant leak could be reducing cooling capacity; user behavior—for example, turning the system on and off frequently—could be preventing the extended run-times needed to cool and dehumidify the space.
Less likely but still possible were a host of mechanical issues: a kinked refrigerant line, a defective valve or thermistor, even a bad compressor. And in the back of my mind was the nagging fear that perhaps I had undersized the system. (In the world of heat pumps and air conditioning, oversizing is far more common—and creates far more problems—than undersizing. We perform thorough…