Summer will be here....

Summer will be here before we know it!  With that said, now is the time to checking the functionality of your air conditioning system.  This includes items such as blower motors, air conditioning compressor, filter dryers, filters, etc.

The air conditioning system is an integrated system that works together with the heating system. Typically this is an automatic system using many of the same controls.  In most cases, the system uses a thermostat that controls both the heat and the air conditioning.  When the climate control switch (thermostat) is OFF, the heater-air conditioning unit is not operational.

The cooling units consist of:

1. The evaporator coil of fin and tube type construction
2.  A refrigerant expansion valve
3.  Filter dryer
4.  Liquid refrigerant receiver tank
5.  The air conditioning compressor
6.  The condenser coil

Additionally there are blower motors, hoses, high and low pressure switches and, of course, adequate refrigerant.

The first thing to check is the evaporator coil.  The main evaporator is typically accessed through one of the baggage compartments.  There is another, smaller one mounted with the driver's heater core. The integrity of the fins and the tubes are critical when it comes to air and oil flow.  The air passes through the evaporator core.  The core cools the air and removes the moisture from it.  The air is then reheated by the heater core.  The evaporator coil must also provide a steady flow of oil to the compressor.  Proper lubrication going from the evaporator to the compressor is essential.

Liquid refrigerant and oil enter the evaporator at the expansion valve and pass through a series of tubes until the refrigerant is completely evaporated.  It is extremely important that both the refrigerant and the oil are at the proper levels when this process is started for the proper operation of the complete system.  The refrigerant boils, absorbs heat from the tubes and fins while the oil, which is saturated with refrigerant, foams as it is forced through the coil by the boiling refrigerant.

If the flow rate is correct and the oil started at the proper level, the oil goes back to the compressor where it is collected in the suction chamber and returned to the crankcase.  Some of the oil is pulled through the suction valves to provide lubrication for the rest of the compressor.

The refrigerant expansion valve is mounted to the evaporator coil and the refrigerant liquid line. The expansion valve will be accessed the same way the evaporator is accessed.  The expansion valve controls the flow of liquid refrigerant going into the evaporator coil.  The valve is designed to maintain the superheat on the gas returning to the compressor.  Superheat is measured is degrees and is necessary to prevent the refrigerant from returning to the compressor in a liquid form.  Superheat is the amount of heat added to a gas to raise the temperature above its boiling point.  Superheat is achieved by adding less liquid refrigerant to the evaporator than what is capable of boiling.  The gas then absorbs the heat from coil to increase a greater temperature - or superheat.

Expansion valve adjustments should not be required unless the valve power head has been replaced or damaged.  Any adjustments should only be performed by a qualified refrigeration mechanic using proper equipment.  Since the most common malfunction is a loose or improperly installed remote bulb, which causes improper  heat transfer, it is imperative that this installation is done properly.

The filter dryer is a disposable type screw-on filter that is mounted in the high pressure liquid line.  It is used to remove foreign matter and moisture from the refrigerant before it reaches the expansion valve.  Any time that work is done on a compressor or on the system in general, this filter dryer should be replaced as a precaution.

This is the first half of the components that make of the air conditioning system in a coach.  Our next blog will focus on the second half, followed by the general operation of the system.

It is our hope that you will check back to continue with our series on air conditioning in preparation for summer.  See you again soon!!