How do you disable the reversing valve on a heat pump so you can run with a straight cool air handler?

Depending on the brand of air conditioner, it is either the removal of the signal voltage to the valve, or the constant application of signal voltage to the valve. Most brands on the market are powering the reversing valve in the cooling mode. This would be easiest as you would have to make no changes if you wish, and only switch your thermostat to Emergency heat instead of heat, effectively not using the heat pump. On Rheems and Ruuds for example, the unit is in cooling mode unless the reversing valve has voltage applied to it. If you have a Rheem or Ruud, no change would be necessary except to change your thermostat to a correctly wired standard version rather than a heat pump specific version. Many electronic thermostats have this built in. Like above, you could also simply use Emergency heat instead of normal Heat switch at the thermostat. Either way, heatpump wiring can be tricky for even a good service tech if they aren't accustomed to working with heat pumps. So its best to have this done by a service company that works with heat pumps a bit.