Question on my heat pump

I have a 4 ton heat pump split system, Goodman brand, that when the Heat Pump is on (to include the outside compressor), there is a definitive humming/noise that gets progressively louder. If I switch it over to Emergency Heat and bypass the Compressor there is no such noise. It is an all electric unit. It only seems to do it after the heat strips heat up and the aux heat kicks out. Any ideas (besides call the HVAC guy).

Without seeing it or hearing it for myself I might be inclined to think it may be the condenser fan motor outside. How old is the unit? That is one of the signs that the motor bearings are worn out and on the way to being T.U.
The reason you don’t hear anything in Emergency Heat is because the Heat pump is no longer running outside. You are basically running like an electric resistance heater inside and the heat pump function is not in operation any more. Get someone to turn on the heat pump while you stand next to the outdoor unit and see if you can determine if the whine or humming is coming from the fan motor. If it turns out to be that you can take it out yourself and go to Johnstone Wholesale Supply House there in Joplin, 602 S. Michigan (206-6640) tell them you are a Home Inspector, start yourself a cash account and never have to pay retail for anything to do with fixing your home again. I buy alot of my test equipment from them at wholesale. If you call them with the numbers off the motor they can tell you if they have one in stock. Oh yeah, They will most likely ask you for the rotation direction of the shaft. It is printed on the motor housing. REal important you get that right.

Doug, I forgot to mention that the noise is coming from the air handler.

Well now, that would be different. The only moving part n the air handler is the circulating fan motor but that would be operating while in Emergency Heat. Scratch earlier post except the part about Johnstone. I will pull my old text book out from HVAC school. It has an extensive troubleshooting section so I will take a look and see if I can come up with any possible scenarios.

I would venture to say that the noise is from the refrigerant circuit (as it only happens when the Heat Pump is working. There is a moving part in there. It is a restrictor (metering device) that slides back and forth between cooling and heating. In heating, it is in the “bypass mode”.

You really need to get in there and find the noise. If you use a stick (old broom handle ect. something non-conductive!!!) and put it on different parts of the unit, you can isolate the source of the vibration (where it is the loudest).

Take a picture of it and post it here.

HI David,
Hadn’t seen you around in a while. I was hoping you would kick in on this. You are correct but then you knew that. I completely forgot about the metering device. I was thinking vibrations but gaffed it off and then the phone started ringing (charities looking for hand outs mostly).

The humming sound in the evaporator of the heat pump system in the heating mode can be cause by improper refrigerant flow, restriction, wrong indoor coil, wrong refrigerant charge and wrong air flow. In the heating mode the system actually uses less refrigerant then in cooling, this is accomplished by storing refrigerant with a check valve in the out door unit in heat mode.

The piston in the indoor coil only meters the refrigerant in the cooling mode so in the heat mode it slides over to allow full flow (metering is now done out side) , when too much or too little refrigerant is present or if a restriction is slowing flow this can cause this humming as it passes through coil by changing the boiling point of the refrigerant in the coil, volume of refrigerant flow and at what point the refrigerant charge changes from liquid to vapor.

Another cause that I see very often is when the coil indoor is mismatched to the capacity of the heat pump.(usually when the out door unit was changed some time in the past but not the indoor coil) In heat pump mode the system stores the “extra” refrigerant out side in a section of tubing with a check valve (one way valve) this is supposed to balance the refrigerant to the proper heating charge, but if the coil is the incorrect size , the refrigerant charge can not balance and will be incorrect or the volume of flow will be wrong. System performance drop, cost to operate goes way up and the system is very noisy. –( This will be a big issue as the new 13 seer units roll out and the indoor coil is not changed to meet the new unit.)

Poor air flow through the coil can contribute to noise too, heat pumps require slightly higher air flow per ton then air conditioners (450 cfm to 400 cfm) but rarely is this in the ducting design, if the air flow is too low (or less common too high) this will change the boiling characteristics of the refrigerant creating noise.

The correct repair is to check the indoor coil for restrictions and proper sizing and cleanliness, remove all refrigerant and weigh in the correct amount as printed on the data plate. Measure air flow for both supply and return and blower speed, make necessary corrections

Heat pumps can be noisy in the heating mode also as the out door temps drop and the performance degrades.

Dave, Is that a variable speed airhandler?

If so, the fan will run faster in E-heat mode and possibly mask a balancing problem that is heard at slower speeds.