HVAC and Engine Cooling Service, Diagnosis and Repair
42%of exam
Service and test conditionsRefrigerant and lubricant selectionEngine cooling and heatingPerformance verification
Refrigeration System Component Diagnosis and Repair
20%of exam
Compressors and protectionMetering and heat exchangersHoses, seals and drainsRefrigerant-path integrity
Operating Systems and Related Controls Diagnosis and Repair
38%of exam
Blowers and drive circuitsDoors and vacuum controlsSensors, networks and calibrationCommand versus response
Quick Facts
- Exam
- ASE A7 Heating and A/C
- Initial Test
- 60 total; 50 scored
- Initial Time
- 75 minutes
- Recertification
- 25 questions; 30 minutes
- Official Domains
- 42% / 20% / 38%
- Work Experience
- 2 years; approved training may count
- Retake
- Wait 30 full days
- Validity
- 5 years
Heat Requires Two Flows
Coolant carries heat; cabin air receives it.
Check coolant circulationCheck door and airflow
Refrigerant Identity versus Appearance
Identification
- Use appropriate refrigerant identifier
- Confirm specified refrigerant before recovery
Appearance
- Container colour is insufficient
- Do not mix based on assumptions
Identify and segregate before service
Pressure Complaint Investigation
- Gauge readings appear abnormal→Verify specified operating conditions
- Condenser pressure excessive→Check airflow, charge and contamination
- Suction low, cooling weak→Investigate charge, restrictions and airflow
- Charge quantity uncertain→Recover and follow specified mass procedure
- Repair complete→Recheck performance under complaint conditions
System Performance and Refrigerant Service
- Test conditions
- Match OEM ambient/load settings
- Pressure pattern
- Evidence, not a unique diagnosis
- Refrigerant identity
- Identify before recovery
- Charge quantity
- Use specified refrigerant mass
- Evacuation
- Remove air/moisture; follow equipment procedure
- Leak testing
- Use compatible approved detection method
- Superheat
- Vapour temperature − local saturation temperature
- Subcooling
- Local saturation temperature − liquid temperature
- Temperature example
- 12°C−3°C=9K; example, not target
Identify Before Connecting
Identify refrigerant, equipment, lubricant and vehicle procedure.
Prevent contaminationPreserve specified chargeVerify repair under test conditions
Oil Family versus Approved Specification
Oil family
- PAG or POE describes base chemistry
- Does not prove compressor compatibility
Approved specification
- Exact OEM oil and quantity
- Preserves intended lubrication and insulation
Select by specification, not family alone
No-Heat Investigation
- Engine warms unusually slowly→Check thermostat and temperature data
- Engine temperature normal→Check coolant level and flow safely
- Heater-flow evidence abnormal→Test valve, pump and restrictions
- Heat source available→Check blend door and airflow
- Service completed→Bleed as specified; verify cabin heat
Refrigerant and Lubricant Decisions
- Section 609
- Separate credential for compensated MVAC service
- ASE A7
- Does not confer Section 609 certification
- Recovery equipment
- Use approved refrigerant-compatible equipment
- Contaminated refrigerant
- Segregate; follow disposal/reclamation procedure
- Compressor lubricant
- Exact OEM specification and quantity
- Electric compressor oil
- Base family alone proves nothing
Coolant Flow versus Air Mixing
Coolant-side fault
- Insufficient heat reaches heater core
- Test valves, pumps and flow
Air-side fault
- Heat source may be adequate
- Test doors, ducts and airflow
Test both sides before replacement
Engine Cooling and Cabin Heating
- Hot pressure cap
- Never open a hot pressurised system
- Coolant selection
- Use approved chemistry and concentration
- Pressure testing
- Stay within specified test pressure
- Thermostat
- Compare warm-up with service specification
- Fan and shutters
- Check command, movement and airflow
- Coolant filling
- Use specified fill/bleed procedure
Heat Flow and Safe Service
- Heater flow
- Check valves, pumps and restrictions
- Hose temperature difference
- Not proof of a blocked core
- Cabin airflow
- Inspect filter, ducts and outlets
- Coolant corrosion
- Check chemistry, grounds and OEM tests
- Electric heater/compressor
- Apply vehicle-specific HV safety procedure
- Dashboard access
- Apply vehicle-specific SRS precautions
TXV Force Balance
Bulb opens; evaporator pressure and spring oppose.
Applies to mechanical TXVElectronic valves use commanded control
TXV versus Fixed Orifice
TXV
- Modulates refrigerant flow
- Commonly paired with receiver-drier
Fixed orifice
- Opening does not modulate
- Commonly paired with suction accumulator
Confirm the actual system design
Component Test Selection
- Pulley rotates, cooling weak→Identify clutch or displacement control
- Compressor debris discovered→Follow component contamination replacement guidance
- Water enters cabin→Check evaporator drain and coolant clues
- Refrigerant leak found→Repair compatible fittings and seals
- Component replaced→Balance specified oil; leak-test system
Compression and Component Protection
- Compressor function
- Raises vapour pressure; drives circulation
- Variable displacement
- Compare command with pressure response
- Clutch diagnosis
- Use specified gap and electrical tests
- Drive coupling
- Inspect belt and breakaway coupling
- Protection devices
- Test; never bypass safety protection
- Oil balance
- Follow replacement-component oil procedure
Heat Exchangers and Metering
- Condenser
- Rejects heat; check airflow and contamination
- Evaporator
- Absorbs heat; check airflow and drain
- Receiver-drier
- Commonly liquid/high side with TXV
- Accumulator
- Commonly suction/low side with orifice
- TXV
- Regulates evaporator-outlet superheat
- Fixed orifice
- Fixed opening; inspect contamination/screens
- Hoses and seals
- Use specified compatible parts
Command versus Response
Requested, supplied, commanded, moved: compare each link.
Scan data shows requestLoaded tests verify deliveryFeedback confirms response
Resistor versus Electronic Blower
Resistor control
- Discrete resistance paths
- High may bypass resistor network
Electronic control
- Module varies motor output
- Diagnose command and loaded circuits
Use the correct wiring diagram
Command versus Actual Response
- Blower command changes only→Test loaded supply, ground and output
- Actuator moves, temperature unchanged→Inspect door/linkage and heat source
- Modes change under acceleration→Test vacuum reservoir and check valve
- Sensor reading implausible→Check circuit and actual temperature
- Module fails communication→Check power, grounds and network
Blower and Load-Circuit Tests
- Voltage drop
- Measure while circuit carries load
- Unloaded voltage
- May conceal a resistive connection
- Resistor blower
- Check selected speed paths
- Electronic blower
- Compare command and module output
- Motor supply
- Check power and ground under load
- Thermal protection
- Find cause before replacing failed protection
- Command versus response
- Scan command does not prove movement
Open versus Ground-Short NTC
Open circuit
- Specified pull-up circuit reads high
- Check connector and continuity
Short to sensor ground
- Specified pull-up circuit reads low
- Check harness and sensor isolation
Confirm circuit before interpreting voltage
Actuators and Air Distribution
- Blend door
- Controls air-mix temperature
- Mode door
- Selects cabin outlet paths
- Recirculation door
- Selects cabin or outside air
- Mechanical cable
- Verify attachment and full travel
- Actuator feedback
- Compare actual and commanded position
- Door calibration
- Run specified relearn after applicable repairs
- Duct leakage
- Air escapes before reaching outlet
Vacuum and Electrical Controls
- Vacuum supply
- Check source under complaint conditions
- Reservoir
- Stores vacuum during supply changes
- Check valve
- Retains vacuum in intended direction
- Vacuum actuator
- Check hose and diaphragm integrity
- Clutch suppression diode
- Respect circuit polarity and protection
- Fan control
- Compare command with loaded-circuit response
- Control panel
- Verify inputs before replacing module
Sensors and Network Diagnosis
- NTC sensor
- Resistance falls as temperature rises
- Pull-up NTC circuit
- Open tends high; ground-short tends low
- Temperature data
- Compare readings with actual conditions
- Sunload input
- Adjusts comfort demand for solar heat
- No communication
- Check power, grounds and network
- Replacement module
- May need coding and calibration
- Repair verification
- Reproduce complaint; check actual performance
Common Traps
Pressure Pattern
A clue needing further tests ≠ Unique proof of compressor failure
Electric Compressor Oil
Exact approved specification ≠ Any oil labelled POE is suitable
Vacuum Hold
One part of prescribed testing ≠ Proof of no pressure-side leak
Coolant Voltage
OEM diagnostic procedure and context ≠ One cutoff condemns every vehicle
Blower High Only
Verify actual resistor-circuit design ≠ Replace resistor in every system
HV and SRS Safety
Complete vehicle-specific disable procedures ≠ Low-voltage disconnect guarantees safety
Last Minute
- 1.60 total; 50 scored; 75 minutes
- 2.Official domains: 42%, 20%, 38%
- 3.A7 does not grant Section 609
- 4.Identify refrigerant before recovery
- 5.Use specified charge mass and oil
- 6.Pressure patterns require corroboration
- 7.No universal evacuation time or target
- 8.Cool engine before opening cooling system
- 9.Match wiring diagram to blower design
- 10.Compare commanded and actual positions
- 11.Relearn modules and actuators as required
- 12.Verify repaired system under complaint conditions
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