Question: Hi, thank you. We have a standard all-electric attic blower with outdoor condenser Carrier AC/heat unit. In the winter, in the middle of the night, the unit outside will make a loud decompression/discharge sound, almost like firing a torpedo. Not a squeak or rattle or gurgle, but a one-time bwwwuuuusshhhh. Once or twice a night, when it’s pretty cold out. loud enough to wake us up. Chris, Buckeye Arizona.
Answer: Thanks so much for your interest in our website and the opportunity to do business with you! From what you describe this sounds like you probably have a heat pump unit and the noise that you are hearing is probably the heat pump going into defrost mode. When a heat pump goes into defrost the reversing valve will shift into cooling mode so the outdoor unit will be defrosted. During this defrost time the heat pump defrost control should turn your indoor electric heaters on so you do not get air conditioned cold air coming out of the registers. If it is cold enough outside you will probably see smoke (moisture) raising above the outdoor unit. I have had heat pump customers call me saying it looks like their outdoor unit is on fire when actually this is normal. Yes, going into defrost mode on some heat pumps can be noisy when the reversing valve shifts the outdoor fan turns off and your indoor electric heaters are energized. I hope this is the problem because this is normal from a heat pump. If it becomes too noisy you might want to call a service tech to come and make sure the operating pressures and refrigerant levels are right. Below we have a real good YouTube video made by Air Comfort Heating and AC which explains how a heat pump system defrosts and what to expect. I hope that you have a blessed day. Steve