AC Repair

Posted by Clay 

AC Vents

Let’s look at how the air conditioning (AC) system works.

The objective of the air conditioning system is to remove the heat from inside the cab of the vehicle. The compressor pumps refrigerant throughout the AC system. This refrigerant is a gas and liquid combination that is compressed and circulated under pressure and is passed through a special valve called an expansion valve that causes the refrigerant to expand.

This expansion makes the refrigerant very cold. This cold gas makes its way via metal lines into the dash area of your vehicle to the evaporator core. This evaporator core is like a small radiator, except it has cold refrigerant circulating inside and not hot antifreeze. A small fan (the AC blower fan which you control from the control panel on the dash) sits in front of the evaporator core and blows air across this cold evaporator and then through the vents inside your vehicle.

The compressor then sucks the warmed refrigerant into the condenser located at front of the vehicle. The condenser will have an electric cooling fan mounted in front or behind it to push or pull air through it to remove the heat from the refrigerant. Some vehicles still use the old fashioned fan blade driven by the engine to pull air across the radiator and the condenser.

A few causes of low air conditioner cooling or no cooling at all at idle are:

  • Lack of air flow across the condenser. Make sure the electric cooling fan motor near the condenser is coming on, or in models that are equipped with a fan blade make sure this fan is turning very fast.
  • Low refrigerant levels. refrigerant level and pressure should be checked by your certified air conditioning mechanic.
  • Overheating. If the engine is overheating, it can have a noticeable negative affect on the air conditioning system. Some cars have two electric cooling fans, one for the air conditioning condenser and the other for the radiator. Make sure they are both working properly. Usually at idle on a hot day with the AC on both fans will be on.

When the vehicle is traveling at freeway speeds, the compressor is pumping the refrigerant throughout the system much faster and harder than at idle. There is a dramatic increase in air flow across the condenser  and the engine is usually operating at a cooler, more efficient temperature as well, thus allowing the air conditioning system to operate efficiently. An air conditioning system that is somewhat low on refrigerant can still feel comfortable at freeway speeds due to the added air flow across the condenser which can overcome the ill effects of slightly low refrigerant. Periodic air conditioning performance checks by your mechanic are the best way to keep the system in great shape.

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