The Summer season is travelling season, and hot weather can make long trips take forever if your vehicle’s air conditioning isn’t working properly. Air conditioning systems are much more durable than they were a couple decades ago but time still takes its toll. Here are some of the more common problems with today’s air conditioning systems.
Air conditioning systems can be separated into two parts. The first part is the refrigeration system. The second part is the air delivery system. Lets look at the refrigeration system first.
Just like home air conditioning (a/c) systems, automotive air conditioning doesn’t make cold; it simply takes away heat. This may seem like a subtle difference but it is significant to diagnosing problems with the system. Heat from the vehicle’s interior is absorbed by a liquid as it evaporates into a gas inside a finned unit called the evaporator. Then it is pumped out to the front of the vehicle by the a/c compressor where the heat is transferred to the air moving through the condenser fins. This heat transfer caused the refrigerant to turn back into a liquid again so the cycle can be repeated.
The liquid used to transfer the heat is R134a refrigerant. Many systems older than about 1994 used R12 as a refrigerant but these systems must be retrofitted to the R134a if refrigerant needs to be added. This adds an additional cost of fittings, oil and sometimes a compressor or hoses, but this is a one-time cost and prevents R12 from damaging the environment.
There are propane and butane-based refrigerants on the market but these can be dangerous. A refrigerant leak inside the car could allow gas levels to build up to an explosive level. These refrigerants will also contaminate R134a, so they can’t be handled with the same equipment. This adds cost.
If refrigerant has leaked from the system, a technician must leak check and repair the system before recharging the system. This is required by the air conditioning regulations. Small leaks usually occur around hose fittings and compressor seals but hoses can also slowly leak, so it is common for systems a few years old to need recharging. Poor interior cooling is a symptom of low refrigerant levels.
Blocked condenser and radiator fins also reduce cooling. If the airflow is blocked the heat cannot be dissipated. Winter fronts must be removed but bugs, leaves and lint can also block airflow. Often the radiator and condenser both look clean, but check between the two units. Blockage in this area limits the cooling capacity of the a/c system.
The second part of the a/c system is the air delivery system. All factory systems are using an air mix system. This means that all the air flows through the evaporator unit where it is cooled if the compressor is turned on, and then the air can pass through or bypass the heater core to add heat to the air flow. Essentially, the system mixes cold air with hot air to achieve the desired passenger compartment temperature.
Two problems typically occur with the air delivery system. Either the airflow is blocked or the control doors don’t move properly. The airflow can be blocked by snow in winter or plugged pollen filters in many newer vehicles. Check for filters first! The next most common blockage is in the fins of the evaporator unit. As the refrigerant evaporates inside the unit, the fins become very cold and moisture condenses on them. Dirt and pollen are trapped in the moisture and drain out holes beneath the vehicle. Sometimes, especially in high humidity areas, the condenser fins remain moist when the vehicle is off and mould starts to grow. This blocks the airflow and may cause unpleasant odours inside the vehicle.
Cleaning the evaporator fins can often be done without removing the unit. Access through small openings for other components allows a fungicide to be sprayed inside the housing. This can be a smelly procedure so it is best left to a repair technician.
Several doors are used to direct airflow inside the heater a/c housing. Basic systems have used cables and levers to move the doors, while many systems now use small electric motors. Regardless of the type of control, if the temperature door doesn’t move all the way to block the heater core, maximum cooling cannot be achieved.
Sometimes foam sealed on the doors comes loose and prevents the doors from sealing. Other times, a cable may have slipped out of adjustment. One problem I often see is objects dropped into the heater a/c housing through the defroster vents. Pens, combs, paper clips – all these small objects can prevent the doors from moving fully. So can sticky soda pop or melted crayons! The message here: keep small objects off the dashboard. If not, the whole heater a/c housing may need to be dismantled to repair the problem.