Why Running An Air Conditioner In Cool Weather Is Dangerous

Man in cold weather

Having a working air conditioner is an essential aspect for many homeowners in Los Angeles. Particularly in the San Fernando Valley, Santa Clarita, and Simi Valley areas, where triple-digit heat in the summer is common. Testing the air conditioner is a key part of the home inspection process. However, running the air conditioner in cool weather can be dangerous to the air conditioner itself.

How An Air Conditioner Works

A pump called the compressor, moves liquid refrigerant between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils.

The refrigeration cycle consists of four stages:

  1. Compression: The compressor increases the pressure and temperature of the refrigerant gas.
  2. Condensation: The high-pressure, high-temperature refrigerant gas releases heat in the condenser, becoming a high-pressure liquid.
  3. Expansion: The expansion valve rapidly reduces the pressure and temperature of the liquid refrigerant.
  4. Evaporation: The low-pressure, low-temperature refrigerant absorbs heat from the indoor air in the evaporator, causing it to evaporate and turn into a low-pressure gas.

The Science Behind the Danger

When the outdoor temperature drops below the recommended threshold, typically around 65 degrees Fahrenheit, several issues can arise that compromise the compressor’s performance and longevity. Firstly, refrigerant requires a certain pressure level to flow optimally through the system. In colder temperatures, the refrigerant may not reach the necessary pressure, resulting in poor lubrication and increased wear on internal components. This can undue stress on the components causing them to wear out.

Secondly, when the outdoor temperature drops below the system’s recommended limit, moisture in the air can condense and freeze on the evaporator coil. The formation of ice on the coil can put a strain on the blower motor. This strain can lead to motor failure.

Moreover, as the ice melts, it can result in water leakage within the unit and potentially damage surrounding areas. The freezing and thawing cycle can weaken structural components, leading to potential issues with ceilings, walls, and flooring.

Manufacture Recommendations

Operating an air conditioner in cooler weather is not recommended by manufacturers of air conditioning systems.

Trane, who also makes units under the brand name American Standard, specifically says their owner’s manual to set cooling no lower than 65 degrees.

Carrier, one of the largest manufacturers of ACs under such brands names as Bryant, Payne, and many more, specifically says in their owner’s manual

“DO NOT OPERATE: Your outdoor unit is not designed to operate when outdoor temperatures are lower than 65_F”

Screen Shot from the Trane Users Manual
Screenshot from the Trane user manual

Temperature Differential

When testing an air conditioner, the inspector checks the air differential. A typical temperature differential when testing a typical air conditioner is around 15 to 20 degrees Fahrenheit between the air entering the evaporator and the air exiting the condenser. In cooler weather, it is near impossible for a typical air conditioner to achieve a 15-20 degree differential as most systems are not designed to cool the interior of a home to 45 degrees.

Standards of Practice

Taking into account what is known about the science of air conditioners and manufacture specifications, the International Association of Certified Home Inspectors (InterNACHI) standards of practice section 3.5 IV(C) states

“The Inspector is not required to: operate equipment or systems if the exterior temperature is below 65° Fahrenheit, or when other circumstances are not conducive to safe operation or may damage the equipment.”

 temperature gun measuring cold air
temperature gun testing for cold air flow

At IM Home Inspection we take great pride in examining and testing equipment during your home inspection. However, we must test equipment in a safe manner. To avoid damaging the AC equipment, we will not test ACs when the outside temperature is below 65 degrees.

To book your inspection in any weather, call 818-298-3405 or book online here.