I just had a ssz160361a heat pump installed 3 weeks ago. It heats perfectly but has an irratic defrost cycle. it is set for 60 minutes, but may defrost anytime. what is the problem

If the unit is running in cold weather than there is ice building up on the coils located outside. This is normal in that the unit is running in heat pump mode heating inside and cooling outside, After the unit detects the ice build up it briefly reverses the cycle heating the outside coils melting(defrosting) the ice which you observe as water on the pad.

The video gives you an example of the defrost cycle!
2012 Trane XL15i Heat Pump Defrost Cycle Steam Show

Take a look at this YouTube page that explains with good videos what are some of the common problems with heat pump noise. The one that seems dominant is the defrost cycle a heat pump goes thru when it melts ice off the evaporative coils. In defrost cycle, The compressor runs but the cooling fan does not, so you will hear a loud buzzing sound and the unit sounds like it is stalled...because only the compressor is running to generate heat to melt coil ice.

https://www.youtube.com/results?search_query=American+Standard+5000+Heat+Pump+makes+a+buzzing+noise
Defrost cycle noise video:
https://www.youtube.com/watch?v=wudLk0WoIVo

All Carrier has on this is installation instructions & field wiring. If your heat pump is freezing up, then check your defrost board to see if the timing jumper for checking the freezestat is set to 30,60, or 90 minutes. If it is set to 90, then set it either to 30 or 60 for the board to check the freezestat more often to go into defrost. Then again, the system could be a little low on refrigerant.

What is the model number of the outdoor unit?

If you need further help, reach me via phone at https://www.6ya.com/expert/thomas_092728000e6acb79

Hi and welcome to FixYa, I am Kelly.

The defrost cycle is usually terminated by a 60 Deg bi-metal thermostat. If the defrost heating element is not heating up the unit will shut off until the internal temp reached 60 Deg F and then restart.

Defrost cycles are 10 - 12 hours apart depending on the defrost control installed so that explains the 12 hr repeat. I really think you have a bad defrost heating element. Here is why I say that...
1. The Defrost cycle is 12 hours after last defrost. (Means the defrost control /board is working)
2. The defrost cycle terminates at 60 Deg F
3. No working defrost element will cause very very long defrost cycles due to the time it takes for the compartment to warm up to 60 deg F and terminate the defrost cycle.

The element is item 33 of this link:
http://www.appliancepartspros.com/partsearch/model.aspx?model_id=5164987&diagram_id=28252332#d28252332

Just looking at the drawing it appears that the Defrost heater and defrost thermostat are an assembly.

You should be able to read resistance end to end on the heater assembly. If you have no resistance it is most likely open / has failed.

The defrost thermostat will read resistance anytime compartment temp is BELOW 60 deg F.

Thanks for choosing FixYa.
Kelly

Hello.I think they are on to something with shortcycling on temp sensor.I think it should be sampling the return air instead of (inside coils ?).A 2*f dead band use to be built in (factory installed) to thermostats to prevent on/off, but not sure in this case.Try a new sensor location(return air) and see if anything changes.

switch for defrost is inside condenser your options are usually 30, 60, 90 minutes. you can not decrease times between defrost it is determined by a coil sensor it senses ice on coil and puts unit into be aware that heatpumps are only effecient down to certin temps.the switch you describe is length of defrost.

I believe the unit you are describing is a heat pump. Heat pump are great when the temperature isn't below 30 With low ambient temps. outside it is much more efficient and comfortable to run aux. electric heat from the heat pump.

Yes. The defrost cycle of a heat pump is actually turning on your airconditioning to heat up the condenser to thaw it out. During this cycle your electric strip heaters "should" be adequate enough to compensate for the a/c being on. At about 30 - 34 degrees outdoor temp there is not enough heat in the air to to adequately heat your home with the heat pump only. Some technitions will use an outdoor thermostat to turn off the heat pump when it is under 34 degrees outside. If you are to cold when its under 34 degrees intall more electric strip heaters.. But if you do this your electric bill may go up significantly.
Welcome to the wonderful world of electric heat pumps (lol).
Good luck.