How to Troubleshoot a Demand Defrost Failure on a Heat Pump

In this video we go out to an existing customer's rental property to look at a Rheem heat pump that was failing to defrost. This unit utilizes a Demand Defrost System which consists of a defrost board, outdoor ambient temperature sensor, and an outdoor coil temperature sensor. This video does not address time temperature controlled defrost systems. If this defrost board would have shifted into a defrost once I shorted the test pins out that would mean that I have a OAT or OCT sensor that has gone out of range since this one was freezing up outside during operation. If the sensors are reading the incorrect resistance compared to the outdoor temperature the unit might not defrost because it would think that it didn't need to because the sensors would be giving it the wrong information. For example, it could be 20 outside but the sensors could be reading that it was 70 outside so the unit would think that it didn't need to go into a defrost. If you have sensors that can be disconnected from the defrost board they can be tested using ohms and referencing a resistance chart along with the outdoor temperature. You just need to know how many K the sensor is and reference the correct chart for it. If the board tested out good and the sensors tested good, I would be looking at a referigerant related issue. In this case, I had a bad board that wouldn't shift into a defrost. In a pinch, you could technically test those sensors soldered to the board if you suspect a sensor is the issue and then temporarily replace it with something you had on hand until you could get what you needed to replace the board and sensors. I also found a failed outdoor fan motor on the unit next to the one I was working on while I was there. I ended up fixing that one up as well. I hope this video helps the new guys out or anyone interested in this type of stuff and how it works. My name is Jake Porter and I am the sole owner & operator of Magnolia Services, LLC. I am a residential HVAC contractor based out of Johnson City, TN. My service area includes: Johnson City, Jonesborough, Unicoi, Erwin, Elizabethton, Hampton, Boones Creek, Gray, Limestone, Lamar, Telford, Watauga, Chuckey, Piney Flats, Bluff City, Blountville, and parts of Kingsport. If you are in my service area and in need of HVAC services, please do not hesitate to contact me at 423-483-7158. Please do not contact me for DIY technical support. Unfortunately, I would need to be able to put my own tools and hands on the equipment in order to assist you. Thanks for watching. Stay safe & best wishes. #hvac #heatpumprepair #heatpump #heatpumps #heatingandcooling #heatingrepair #heating #hvacrepair #magnoliaservicestn #magnoliaservices #jakeporterhvac #rheem #hvaccontractor #heatingoptions #heatingandcoolingrepair #defrostboard #defrost #defrosting #demanddefrost