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A/C Operation

A/C Operation. Basic Operating Principles. Refrigerants.

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A/C Operation

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  1. A/C Operation Basic Operating Principles

  2. Refrigerants R-134a has a very low boiling point, -15o F (-26o C) at sea level. This boiling point will increase as the pressure is increased. When a liquid boils, it changes to a gas. Heat is added or absorbed during the boiling change of state. A gas condenses into a liquid at the same temperature as the boiling point. Heat must be removed for a gas to condense to a liquid.

  3. R-134a Pressure-Temperature Refrigerant in both the low and high sides is a saturated vapor; a vapor in contact with liquid. The pressure of a saturated vapor is directly related to the temperature. Note that the Pressure-Temperature Relationship for R-12 and R-134a are very similar. Animation: Pressure-Temperature Relationship

  4. A/C System A/C systems have two major parts: The high side starts at the compressor and ends at the expansion device (orifice tube or TXV). The low side starts at the expansion device and ends at the compressor. Animation: A/C Systems, OTA/C Systems, TXV

  5. Low Side Operation The pressure on the liquid R-134a drops as it passes through the orifice tube. The low pressure allows it boil and absorb heat in the evaporator.

  6. Evaporator Heat from the relatively warm air passing through the evaporator causes the refrigerant to boil.

  7. Heat Transfer Heat transfers from the air passing through the evaporator to the liquid R-134a. This heat boils the refrigerant, causing it to change state to a gas. The heat transfer cools the air.

  8. Accumulator • The accumulator: • Stops any liquid from going to the compressor • Contains the desiccant to remove any traces of water from the refrigerant • Collects refrigerant oil and • allows it to return to the compressor • Provides space for refrigerant expansion

  9. TXV Operation A TXV meters the refrigerant flow into the evaporator so it will all boil and become a vapor. The valve opening size is controlled by the pressure on one side of the diaphragm (green) (from thermal bulb & cap. Tube), pressure on other side of diaphragm (blue) (evaporator), and the superheat spring.

  10. Compressor Operation This double piston strokes back and forth as the swash plate rotates. In this view, the piston is moving to the left, the right end is on a suction stroke with refrigerant entering from the suction port, and the left end is on a discharge stroke, forcing refrigerant out the discharge port. Animation: Swash Plate Compressor

  11. Rotary Compressors Many modern vehicles use a vane (shown) or a scroll compressor. The pumping member of these compressors rotate to increase the pressure and move the refrigerant into the high side. Animation: Vane Compressor

  12. High Side Operation The main purpose of the high side is to return liquid refrigerant to the expansion device.

  13. Compressor Action The compressor increases both the pressure and the temperature of the refrigerant gas.

  14. Condenser Operation Heat is transferred from the refrigerant to the air flowing through the condenser. Removing heat from a vapor will change it to liquid. Refrigerant temperature should drop about 20 degrees F as it passes through the condenser.

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