It is April and we are getting asked about testing the air conditioner. The standard and appropriate response is,”..not yet.” The client response is typically, “…why not?” There is a pretty simple and clear reasoning behind the strict guidelines most home inspectors follow. In fact, most air conditioning manufacturers and HVAC professionals agree, an outdoor condensing unit should be be run in cold weather for any reason.
The reason behind this prohibition is the oil used to lubricate the compressor is a weight that does not lubricate well when it is cold. The lubricant for an air conditioner is not unlike the lubricant for your car. There are different grades like summer-weight and winter-weight. The summer-weight oil used in the standard air conditioner is a heavy grade oil and only works well in the warmer months or during warmer conditions. In cold weather, the oil is too thick for safe operation of the system.
Most HVAC technicians and home inspectors won’t operated the central air conditioner unless the daytime temperatures are well above 65 degrees for at least 24 hours. This would limit the window for many locations of the country. A good median to consider is May through September. The only exception would be those units with a crankcase or sump heater. This is a heating strip placed around the compressor and oil reservoir with the hopes of keeping it warm and moving. There are even some, more sophisticated units, with low-ambient temperature sensors that prevent cold weather operation.
If you do not know if there is a crankcase heater or you do not know if your unit has a thinner grade of oil do not take the risk. Do not operate your central air conditioner until the 24 hour temperatures are over 65 degrees. The risks are too high. Operating a unit at that temperature could otherwise damage a perfectly good operating unit.