My Sanyo Heat Pump will not turn on. Actually it did turn on once this winter and the temperature was up to 90 degrees. Then it turned on once this summer and the temperature was in the 60's.

Nothing is wrong with unit ,that's how heat pump work ,you should also have a 2 stage heat which most likely electric heat so when heat pump cannot keep up with temperature the electric heat should kick in and heat up the space

You have a heat pump.
Once the outdoor temperature falls below 36 degrees, heat pumps will sharply lose their ability to heat.
If you are getting a 72 degree indoor temperature when the outdoor temperature is 28-30 degrees, the heat pump is performing up to spec.
On heat pumps, the air coming out of the nearest air vent to the unit should be heated approximately 40 degrees warmer than the air entering the unit.
If you have a 70 degree indoor air temperature, the heat pump should be supplying 110 degree air at the closest air vent to the indoor unit.
Gas heat is a much better heating source where outside temperatures are commonly below 36 degrees.
Even electric furnaces perform better than heat pumps under these conditions.

See if it happens only when your temperature of the room is more than 3 degrees of your setpoint temperature. Since you have a heat pump, the auxiliary (electric heat strips) is use for backup of the heat pump when it can't keep up. The heat pump will run by itself if it can maintain temperature within a couple degrees. If it is too cold outside to handle the load or you set the temperature more than 2 degrees past room temperature, the auxiliary will turn on. The thermostat has a memory of how long it takes to reach desired temperature. If it goes into auxiliary mode trying to satisfy setpoint during the last call for heat, it will start the next call for heat in both aux & heat pump mode until the thermostats algorithm (timed program) allows only the heat pump to run. Not sure if you have an air to air, or geothermal heat pump. The outside air temperature will affect only the air to air system ie. when the temps drop outside, the heat coming out of your vents will be cooler...the air to air systems drops efficiency when the outdoor air drops.

If your thermostat has an emergency heat setting this means you have a heat pump system.
Yes you need to set the thermostat to heat for heating the house.
The emergency heat setting should never be used unless your outside unit is not functioning.
The emergency heat setting overides the heat pump (the outside unit will not be energized).
The emergency heat setting will run the auxillary heat (heat strips) only.
When the thermostat is set in the heat position the heat pump will run to heat your house.
If the heat pump can't keep up (extreme cold) then then the auxillary heat will kick in to augment the heat pump until it satisfies the thermostat settings. If your room temperature gets 2 degrees below your thermostat setpoint, your auxillary heat will kick on. Example, say you are going to be gone a couple of days and you turn your heat down to 60 degrees. When you return and it is 60 degrees in your house, you turn the thermostat up to 70 degrees. Since you are turning the temperature up 2 degrees or more (10 degrees in this case) from the 60 degree room temperature then the heat pump will come on and the auxillary heat strips. The unit will continue heating like this until the temperature in the house gets to 69 degrees and the heat strips will turn off and the heat pump will continue to run until the 70 degree setpoint is reached.
Hope this helps.
SeagullAC

what it sounds like happening is the unit is realizing it is falling behind most thermostat s have a 3 degree deadband if they fall 3 degrees or more at a time after running for so long then it will bring on the emergency heat which is located in your inside unit... when it gets really colds and you see this you need to go outside and look is the outside unit still running and is it freezing up on you...also if running check the larger of two pipes make sure the large pipe is hot to touch...based on the description you have given the thermostat is calling for emergency heat but for some reason is not bringing it on or there is a problem with the emergency heat.... hope this helps out some
repost with any additional questions...

heat rises yes you will save energy this way

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.

It shouldn't have any bad effects on the display. When LCD panels get cold they may exhibit slow response time, like trails or a persistent display when action is moving. As long as you don't experience SUDDEN temperature changes you should be OK

Heat pumps do loose their heating capacity and efficiency as temps drop. If you decide to rely on a heat pump you may want to make sure that your system has a back up heat strip, maybe even controled with an outdoor thermostat, if that is an option. The Mitsubishi is a great product.