1 Air Conditioning Pressure Switches

2 High Pressure switch Used to protect the compressor When condensing temp gets too high Reads High Side Pressure Located in condensing unit Can be wired line duty or control voltage Used to protect the compressor When condensing temp gets too high Reads High Side Pressure Located in condensing unit Can be wired line duty or control voltage

3 High Pressure switch cont… Opens on rise in pressure/ closes on drop Adjustable type -normally set to open at 350 psi with a 75 differential Non-adjustable type -are pre-set to pressures -re-set button must be pushed Opens on rise in pressure/ closes on drop Adjustable type -normally set to open at 350 psi with a 75 differential Non-adjustable type -are pre-set to pressures -re-set button must be pushed

4 Types of High pressure switches

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9 Low pressure Switch Safety switch Opens on pressure drop/ Closes on pressure rise Condensing unit de-energized Indoor Blower motor remains running Safety switch Opens on pressure drop/ Closes on pressure rise Condensing unit de-energized Indoor Blower motor remains running

10 Low pressure Switch cont… opens at about 55 psig (R-22) located in condensing unit wired line duty or control voltage opens at about 55 psig (R-22) located in condensing unit wired line duty or control voltage

11 Low pressure Switch cont… Opens due to: Restricted air flow- registers, return grills, loose belt, dirty evaporator Low refrigerant charge- leaks Opens due to: Restricted air flow- registers, return grills, loose belt, dirty evaporator Low refrigerant charge- leaks

12 Types of Low Pressure switches

13 Types of Low Pressure switches

14 Types of Low Pressure switches

15 Low Ambient Control Cycles condenser fan On and Off Runs system at Design pressure -when outside ambient temp. are low -found in some residential units -usually found in commercial systems Cycles condenser fan On and Off Runs system at Design pressure -when outside ambient temp. are low -found in some residential units -usually found in commercial systems

16 Low Ambient Control cont… Wired in line side only -best to wire after “C” on condenser fan Closes on pressure rise (250 psig) Opens on pressure drop (200 psig) -50 psig differential Wired in line side only -best to wire after “C” on condenser fan Closes on pressure rise (250 psig) Opens on pressure drop (200 psig) -50 psig differential

17 Low Ambient Control cont… There are different types of LAC’s: pressure sensing condenser discharge air sensing liquid line sensor There are different types of LAC’s: pressure sensing condenser discharge air sensing liquid line sensor

18 Low Ambient Control cont… Function LAC provides: High condensing pressure Good refrigerant flow Keeping low side temp above freezing Function LAC provides: High condensing pressure Good refrigerant flow Keeping low side temp above freezing

19 Sail Switch Mechanical switch that proves air flow Located in ductwork Switch is open when no airflow is present Will close when fan comes on Prevents freezing of evaporator coil due if indoor airflow is not established. Wired in “Y” circuit Mechanical switch that proves air flow Located in ductwork Switch is open when no airflow is present Will close when fan comes on Prevents freezing of evaporator coil due if indoor airflow is not established. Wired in “Y” circuit

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