How can I test cooling equipment in winter?

You can only test cooling equipment when you can turn the equipment on.  Most manufacturers deem it appropriate to turn cooling equipment on once the temperature is 65 degrees or higher.  Heat pumps can be tested in heating or cooling mode and don't need to be tested in both; if it works in one mode, it will work in the other. 

If you install an air conditioner during the heating season, you can do testing once the weather warms up.  If your customer is seeking a rebate for the equipment, the testing in cooling mode must be submitted to the utility company by September 30th.