Michigan Mechanic Certification- HVAC
Symptoms of a failing ambient temperature switch
A bad temperature switch could cause an inoperative clutch or input problems
Typical cause of a clogged orfice tube
A clogged orifice tube is typically caused by compressor failure
Low side pressure is high and high side pressure is low
An internally faulted compressor or a stuck open expansion valve
Symptoms of an overcharged system
Both the low and high side pressures will read higher than normal
What are CFCs
CFCs are a compound that destroys the ozone layer when released into the air
How is compressor clutch cycling operated
Cycling is accomplished through the engaging and disengaging of an electromagnetic clutch which is actuated by a module, relay and or switch
Symptoms of low coolant
Engine overheating and no heat from the HVAC system
Symptoms of a clogged orifice tube
Frost forming around the restricted area
Orifice expansion tube operation
Has a valve that can vary the size of the opening to allow more or less liquid refrigerant through to the evaporator
Orifice expansion tube purpose
High pressure liquid enters, low pressure liquid leaves
Purpose of a fixed orifice tube
High pressure liquid enters, low pressure liquid leaves
What is operating pressure of high side pressure?
High pressure should be between 170psi-230psi
Compressor clutch cycling operation
If the pressure becomes too high, the compressor clutch is cycled off, and if the pressure is too low, the compressor clutch is cycled on.
Reciever drier location
Located on the high side of the system between the condenser and the evaporator
Cause of low heater output
Low coolant level, clogged heater core, leaking heater core
Purpose of a compressor
Low pressure gas enters and high pressure gas leaves
Purpose of a condenser
Low pressure gas enters and high pressure gas leaves
Purpose of a evaporator
Low pressure liquid changes into low pressure gas
What is operating pressure of low side pressure?
Low pressure should be between 20psi-40psi
Reciever drier purpose
May contain a filter or strainer to catch and trap foreign particles and dirt
Effect of moisture in the system
Moisture in the a/c system will turn to acid and destroy all the components in the system
Ambient temperature switch purpose
Monitors temperature by increasing or decreasing with resistance as temperature changes
Both low side and high side pressures are high
Overcharge, faulty restriction device or blockage of the high side
Cooling system leak diagnosis
Pressure test or dye test
Symptoms of a failing compressor
Pressures are going to be equal
R-12 background
R-12 is Freon and it destroys the ozone layer due process of releasing CFCS into the air
What replaced R-12
R-134a
What causes CFCs
R12
What replaced R134a
R1234yf
Low side pressure is low and high side pressure is high
Restriction in a line or a stuck closed expansion valve
Symptoms of a failing evaporator
Symptoms of a failed component could be a leak, sniffer test required
Symptoms of a failing condenser
Symptoms of failure or restriction are a high high-side discharge of pressures
Effect of outside temperature & humidity on a system
Temperature and pressure are directly related. The higher the ambient temp, the higher your AC pressures will be. Higher pressure's will lead to a higher outlet vent temperature. Essentially, the air conditioning system does not work as well under extreme heat and humid conditions
Heater core operation
The blower motor blows air through the heater core fins and is warmed through the principle of conduction
How will the compressor act on an overcharged system
The compressor will run for a few seconds then turn off for long periods of time
Purpose of a radiator
The purpose of the radiator is to dissipate heat that is picked up by coolant in the engine into the air passing through its fins and tubes
Purpose of the thermostat
The purpose of the thermostat is to trap the coolant in the engine until it reaches it operating temperature
Heater core hose routing
The supply hose from the heater core should run from the closed side of the thermostat to the heater core and the return hose should run from the heater core to the engine
Heater control valve purpose
This valve controls the flow of the coolant to the heater core to control the temperature of the air desired by the operator
Radiator cap testing
To test pressure test it using an adapter and a coolant pressure tester and the value marked on the pressure cap
Causes of both low side and high side pressures are low
Undercharge or restriction at either the orifice tube or expansion valve
Compressor clutch cycling testing
power and ground should be sufficient and the clutch should only have 3-5 ohms of resistance
