Troubleshooting Puzzle: An Under-Performing Heat Pump
Figure one. Courtesy of Jim Johnson
In this troubleshooting situation, you are responding to a customer’s complaint about their heat pump, and you’re not the first technician called in to service this equipment. The customer’s description of the problem is that the unit is “running a lot, and not keeping the building warm.”
This residence is a rental unit, and the equipment is a package unit shown in Figure One. Upon your arrival at the customer’s home, you find the following conditions:
- The indoor temperature is 65° F.
- The thermostat is set at 75° and the fan switch is in the AUTO position.
The customer, whose complaints began when they moved in during the summer, confirms that the unit has been operating for over two hours. They also provide you with copies of the work orders from three previous service calls. On the first visit, the technician reported that refrigerant was added. The work order also shows no air filter was found, and one was installed.
On the second visit, the technician’s report shows that an indoor fan relay was replaced due to the suspicion that it was intermittently preventing the indoor air handler from operating. A work order for a third visit states that the indoor fan motor was replaced due to the suspicion that it was intermittently overheating and kicking off on its internal overload protector. Also, on this visit, refrigerant was added again.
The customer also reports that by this time, the weather was mild and since they didn’t use the equipment until the temperature dropped low enough to require heat, they didn’t follow up any further with the service company that had responded to their requests for service.
Moving to the roof to conduct an initial inspection of the equipment, you note that the compressor and outdoor fan motor are operating. You also confirm that the design of this system is such that the filter is located in the return air duct assembly. Removing the cover on the filter slot, you find that the filter is the proper MERV rating for this equipment.
As your next step, you go back inside the house and, using an anemometer, you check the air flow at a bedroom supply register and find it to be 90 CFM.
Then, you return to the roof and remove the access panel to the air handler. With the air handler remaining in operation, you go back into the residence to perform a second test on the same supply register. Your test shows that the air flow is now 120 CFM.
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