Study guide
6.2 Cooling System Tests, Radiators, Hoses & Clamps, Coolant Pumps, Flush & Refill
ASE T7 HVAC Medium/Heavy Truck
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1 Chapter 1: Exam Overview, Safety & Complaint Verification
1.1 ASE T7 Exam Format, Task List & Question Strategy 1.2 Shop Safety, PPE & Identifying the Truck's Power Source 1.3 Verifying the Complaint: Interview, Records, TSBs, Noises & Sensory Checks
2 Chapter 2: HVAC Performance Testing, Gauges & Leak Detection
2.1 Systematic HVAC Performance Testing & Diagnostic Methodology 2.2 Manifold Gauge Pressure Analysis & Diagnostic Logic 2.3 Superheat and Subcooling Analysis in Commercial Trucks 2.4 Refrigerant Leak Detection, Purity & Identification
3 Chapter 3: Refrigerant Management, Recovery, Oil & Charging
3.1 Environmental Regulations, Safety & Refrigerant Properties (R-134a & R-1234yf) 3.2 Refrigerant Recovery, Recycling & Deep Evacuation 3.3 Refrigerant Storage, Recovery-Cylinder Air Checks & Service Equipment Care 3.4 Compressor Lubricants (PAG vs. POE), System Flushing & Cleanliness 3.5 Accurate System Charging, Charge by Weight & Field Pitfalls
4 Chapter 4: Compressors, Drives, Clutches & Protection Devices
4.1 Heavy-Duty Truck Compressor Types & Operating Principles 4.2 Compressor Mountings, Drive Belts, Pulleys, Tensioners & Idlers 4.3 Magnetic Clutch Diagnosis, Air Gap Adjustment & Electrical Circuits 4.4 Compressor Failure Analysis, Protection Devices & System Cleanup
5 Chapter 5: Heat Exchangers, Metering, Storage & Refrigerant Lines
5.1 Condensers, Ram Airflow & Fan Clutch Operation 5.2 Evaporator Cores, Moisture Drainage & Freeze-Up Controls 5.3 Metering Devices: Thermal Expansion Valves (TXV) & Fixed Orifice Tubes 5.4 Refrigerant Storage & Desiccant: Receiver-Driers vs. Accumulators 5.5 Refrigerant Hoses, Lines, Fittings, Service Ports & Seals
6 Chapter 6: Engine Cooling Systems, Fans & Airflow Devices
6.1 Diesel Engine Cooling System Integration & Thermal Management 6.2 Cooling System Tests, Radiators, Hoses & Clamps, Coolant Pumps, Flush & Refill 6.3 Engine Cooling Fans, Shrouds, Grille Shutters & Electric Condenser Fans
7 Chapter 7: Cab & Sleeper Heating, Temperature Control & Window Fogging
7.1 Heater Core Diagnostics, Clogging & Integrity Testing 7.2 Coolant Flow Control: Valves, Auxiliary Pumps & Sleeper Lines 7.3 Diagnosing Outlet Air Temperature Problems & Window Fogging
8 Chapter 8: Air Distribution, Actuators & Blower Systems
8.1 Plenum Air Doors: Blend, Mode & Recirculation Control 8.2 Air-Operated (Pneumatic) HVAC Controls & Actuators 8.3 Blower Motors, Speed Resistors & Pulse-Width Modulated Modules 8.4 Duct Systems, Cabin Air Filtration & Airflow Diagnostics
9 Chapter 9: Electronic Controls, Networks, Sleeper Systems & APUs
9.1 Electronic Automatic Temperature Control (EATC) & Sensor Operations 9.2 HVAC Control System Types, Control Panels, DTCs & Module Configuration 9.3 Wiring Schematics, Clutch Relays & J1939 CAN Bus Diagnosis 9.4 Sleeper Cab Climate Systems & Auxiliary Power Unit (APU) Integration
6.2 Cooling System Tests, Radiators, Hoses & Clamps, Coolant Pumps, Flush & Refill
Key Takeaways Explain This Topic AI
ASE T7 task C3 requires testing the engine cooling system for leaks, protection level, contamination, coolant level, temperature, coolant type, and additive (conditioner) concentration.
A refractometer reads freeze protection for both ethylene and propylene glycol coolants and is more accurate than a float hydrometer.
Inadequate freeze protection can freeze and rupture heater core tubes, a common failure on sleeper heater cores and lines exposed to cold.
In a combustion-leak (block) test, test fluid that changes color from blue to yellow shows exhaust gas in the coolant from a head gasket, cracked head, or failed cooler.
Silicone heater and coolant hoses need clamps designed for silicone, such as constant-tension or lined T-bolt clamps, because standard worm clamps can cut into the hose and let it cold-flow and leak.
Last updated: September 2026
Why Cooling Service Is on an HVAC Test
The cab and sleeper heater cores are branches of the engine cooling circuit, and the A/C condenser shares the cooling package's airflow. Weak coolant, air pockets, a failing pump, or a leaking hose therefore produce HVAC complaints: no heat, cold sleeper, fogged windows, or a frozen heater core. This section covers tasks C3, C4, C5, C6, and C8. Thermostat operation and the physics of pressure caps and surge tanks are in the diesel cooling integration section, and fans are in the next section.
Cooling System Tests (C3)
Test Tool or Method What It Tells You
Coolant level Surge tank marks (check cold), low-coolant sensor Low level starves heater cores first because they sit high
Freeze protection Refractometer with ethylene glycol (EG) and propylene glycol (PG) scales Freeze point; hydrometers read PG poorly and need temperature correction
Coolant type Label, maintenance records, test strips Conventional, NOAT, or OAT. Color alone is not reliable
Additive (conditioner) concentration Test strips for nitrite (and molybdate) Whether supplemental coolant additive (SCA) must be added or held back
Contamination Look, smell, oil test, fuel test, sediment Oil film (oil cooler), fuel odor (injector sleeve or cup leaks on some engines), rust, scale, sludge from mixed coolants
Combustion leak Block tester with color-change fluid; bubbles in the surge tank Exhaust gas in coolant from a head gasket, cracked head, or failed EGR cooler
Pressure test Hand pump on the fill neck, to the cap rating External leaks at hoses, pump, and radiator; a drop with no external leak points to an internal leak
Temperature Scan tool coolant temperature compared with an infrared or contact thermometer Thermostat operation, sensor accuracy, hot spots
Stray voltage Digital multimeter from coolant to engine ground Measurable voltage, especially rising when electrical loads switch on, indicates a poor ground or leakage
Additive balance: conventional and NOAT coolants depend on nitrite (and often molybdate) to protect wet cylinder liners from cavitation. Test with the strips specified for that coolant, then add SCA or install the correct filter per the chart. Do not simply add SCA each service, because over-concentration causes silicate dropout and deposits that plug heater cores. Fully formulated OAT coolants use different test methods and extender products; follow the coolant maker's instructions.
Freeze damage: when freeze protection is inadequate, coolant can freeze in the coldest, highest, and most exposed places. Those are sleeper heater cores, under-cab heater lines, and auxiliary heater circuits. Expanding ice splits heater core tubes and cracks housings. Ruptured heater core tubes after a cold snap point to incorrect coolant protection, not a bad heater valve.
Hoses, Lines, Fittings, and Clamps (C4)
Inspect hoses by squeezing them near the ends with the engine cool. Replace hoses that are soft or spongy, hard and cracked, swollen, or oil-soaked.
Electrochemical degradation (ECD): an electrical potential between the coolant, engine, and radiator can attack a rubber hose from the inside, usually within a couple of inches of the ends. You may feel gaps or channels inside when squeezing near the fitting. Replace affected hoses with ECD-resistant EPDM hose and correct the grounding.
Silicone hoses are common on heavy trucks. They last long but "cold-flow" under standard worm clamps, which can bite into the surface. Use constant-tension (spring or Belleville washer) clamps or lined T-bolt clamps as specified, and torque them to the clamp maker's value.
Heater lines to the sleeper may be long hoses, steel tubes, or a mix, with quick-connect fittings. Check for chafing along the frame, secure the clamps, and inspect plastic quick-connect latches and O-rings.
After replacing hoses, pressure test the system and recheck clamp torque after the first heat cycle if the clamp maker calls for it.
Radiator, Pressure Cap, Surge Tank, and Mountings (C5)
Radiator: inspect for debris packed between the cores, bent or corroded fins, and leaks at tube-to-header joints and at plastic tank crimp seams. With the engine hot, an infrared scan (or a contact thermometer) across the core finds cold bands , which are plugged tubes. A radiator that runs cool at the bottom while the engine overheats under load is restricted.
Pressure and fill caps: test the pressure valve at its rating and check the vacuum valve, as described in the diesel cooling integration section. Use only the rated cap.
Surge (expansion) tank: look for cracks, especially at mounts and fittings. Check the deaeration and fill lines for kinks, and confirm the level sensor works.
Mountings: truck radiators and cooling modules sit on rubber isolators and brackets that absorb frame twist and vibration. Worn or missing isolators, broken brackets, or loose tie rods let the module move, which cracks tanks, chafes hoses, and opens gaps in the air seals. Replace isolators and restore every seal and brace after service.
Coolant Pumps and Drives (C6)
Engine coolant pumps may be belt-driven or gear-driven . Auxiliary electric pumps are used for sleeper heat, APU coolant loops, and some coolers.
Weep hole: the seal vents through a weep hole. A small stain may be normal per the OEM, but active dripping or a steady trail means the seal has failed.
Bearing: check for shaft play and noise. For belt-driven pumps, check the belt as described in the compressor drive section.
Impeller erosion or slippage reduces flow without external symptoms. Watch for poor heat at idle, especially in the sleeper, with normal-looking temperatures on the highway.
For electric auxiliary pumps, check voltage and ground under load and the pump's current draw, as covered in the coolant flow control section.
Flushing, Refilling, and Bleeding (C8)
When: contaminated coolant (oil, fuel, rust, mixed types), the wrong coolant, or a scheduled change.
Drain completely: radiator drain, engine block drains, and low points in heater lines. Capture and recycle or dispose of the coolant as regulations require.
Flush with an approved cleaner if there is scale, sludge, or oil contamination, then rinse. Remove heater cores from the flush path if they are plugged, and back-flush them separately at low pressure.
Filters: install the correct coolant filter, charged or blank as the coolant type requires.
Refill with the OEM-approved coolant at the right concentration, premixed with clean water. Fill slowly or use a vacuum refill tool , with heater valves open and the HVAC set to full heat so the heater circuits fill.
Bleed air at the vent plugs and petcocks, including high sleeper cores. Run the engine to operating temperature with heater valves open and any auxiliary pump running.
Verify: recheck the level cold, pressure-test, confirm heater hose temperatures, and confirm the protection level with a refractometer.