Many people may wonder why HVAC companies will not maintain or recharge your AC unit on a cold day. It is simply not an effective way to test freon levels.
Cold Temperature Charges
You can work on these units in the cold and some technicians use “insulated blankets” to wrap the outside condensing units with to create a head pressure rise. This simulates a hot day, they can then add or remove refrigerant based on that reading. The problem with this technique is the head pressure rise is more of an estimate. With this estimate of head pressure you are not getting an accurate reading therefore it would be easy to overcharge or undercharge the unit.
This results in you as the customer being inconvenienced by your unit still having issues and possibly having to pay for the same service to be done on a hot day. When charging your unit on a hot day you will get a accurate reading therefore resulting in a cheaper repair and peace of mind that your unit will be operating correctly. This is the preferred method to work on AC units because we know we are getting a correct reading and will not have to worry about an unhappy customer or wasted time. The correct temperature for recharges is 70-75° F.