Tempstar Heat Pumps secondary heat isn't running during its Defrost Cycle

I am wondering if my heat pump's second-stage heat is not turning on during its defrost cycle.
Tempstar XL 5300 Heat Pump, installed new 5-07. Installation instructions 331823-701 (Oct 2005) Trane Air Handler, installed new in attic about 1999.
I know that during very cold weather the second-stage heat works because I can feel the hotter air at the registers and see the Em. Heat icon on the thermostat.
As I read the Installation Instructions, it says:
"Defrost cycle is pre-set for 90 minutes." [but can be 30/60/90].
and
"Defrost Mode is identical to Cooling Mode except that outdoor-fan motor stops and second-stage heat is turned on to continue warming conditioned space."
The defrost cycle seems to have a 'normal' setting of 10 minutes, which seems kind of long to blow cold air when you need warm.
I'm not sure if this occurred during its first winter or not, but its definitely happening now in its 2nd winter.
Could this be an improper setting which can be changed..or something else? I'd like to troubleshoot this as much as possible before I call the installer because he's kind of a jerk and tries to talk his way out of having to come out for anything.
Thanks
Brian
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