I have an Armstrong AC/Heat pump. It is new and just installed this past summer. The A/C unit worked fine all summer and the heat pump unit worked OK until the outside temperature dropped below 50 degrees. Now the unit won't kick on at all .The blower inside the house kicks on and the thermostat says heat on . What could be the problem?

Actually your unit should be still under the first year warranty so I would not mess with it. You will be better served by calling the contractor/HVAC company that installed it and having them look at it.

As far as problems are concerned it could be as simple as a tripped breaker of a fuse in the outside disconnect for starters.