1.2 Shop Safety, PPE & Identifying the Truck's Power Source

Why Identification Comes First

The first task in the T7 list asks you to identify the vehicle as gasoline, diesel, alternative-fuel, or high-voltage electric powered and to verify that manufacturer safety procedures and personal protective equipment (PPE) are in use. Climate systems are now connected to every power source on a truck. An electric truck's A/C compressor and cab heater may run on a traction battery of several hundred volts. A natural-gas truck carries fuel at very high pressure behind the cab. A diesel's HVAC may depend on the air brake system or a vacuum pump. The right tools, test methods, and hazards all depend on which truck is in the bay.

How to Identify the Power Source

On electric and hybrid trucks the refrigerant circuit often cools the battery as well, through a chiller, so an HVAC complaint can come with battery-temperature warnings. Some compressor or heater tests require commands from the OEM diagnostic software rather than simple jumpers.

High-Voltage Safety Procedure

Only technicians trained on the specific platform should work on high-voltage components. The general sequence in OEM procedures is:

1. Park and secure: key off, key removed, parking brake set, wheels chocked, and the 12 V system disconnected if the procedure calls for it.
2. Isolate the high-voltage system: remove the service disconnect or follow the OEM isolation steps, then lock out and tag out.
3. Wait: allow the specified time for capacitors in inverters and motor drives to discharge.
4. Verify zero voltage: use a meter rated for the category and voltage, check it on a known live source, test the circuit, then recheck the meter on the known source (live-dead-live).
5. Wear rated PPE: insulating rubber gloves rated for the voltage (ASTM Class 0 gloves are rated 1,000 V AC), worn under leather protectors, air-tested for pinholes before each use, plus eye protection and non-conductive tools where specified.

Remember the refrigerant-oil link: an electric compressor needs the high-insulation oil its maker specifies. A recovery machine that injects ordinary PAG can create an insulation fault.

Alternative-Fuel Hazards

• CNG (compressed natural gas) is stored at up to about 3,600 psi. Natural gas is lighter than air, so a leak rises and can collect near the ceiling, where heaters and lights can ignite it. Inspect cylinder labels and brackets, never weld or grind near cylinders or lines, and follow the shop's gas-detection and ventilation rules. NFPA 30A addresses repair garages that service gaseous-fuel vehicles.
• LNG (liquefied natural gas) is cryogenic and can cause cold burns. Tanks vent vapor as they warm, so wear face and hand protection near fittings.
• Propane (LPG) is heavier than air and collects in pits, drains, and low areas. Keep ignition sources away from pits.

Refrigerant, Coolant, and Running-Engine Safety

Refrigerant work (from SAE practices summarized in ASE's Section 609 training):

• Wear safety goggles with side shields and insulated gloves. Liquid refrigerant flashing to vapor causes frostbite. Warm the affected area with lukewarm water and get medical help.
• Work in a well-ventilated area. Refrigerant vapor displaces oxygen, and R-1234yf is mildly flammable, so keep it away from sparks and flame.
• Never weld, braze, or use a torch near a charged system. Heat decomposes fluorinated refrigerants into hydrogen fluoride and other toxic gases.
• Never pressurize a system with a refrigerant-air mixture or with shop air for leak testing.
• Never add refrigerant to the high side of an operating system; pressure can back-feed into the container.

Cooling-system work: never open a hot, pressurized cooling system. Let it cool, then relieve pressure slowly with the cap's first stage or a relief valve. Coolant is toxic and must be captured, not drained on the floor.

Running-engine tests are common in T7 diagnosis, so:

• Use exhaust extraction and chock the wheels.
• Keep hands, hoses, and tools away from the engine fan. An on/off or electronically controlled fan clutch can engage without warning when A/C head pressure or engine temperature rises.
• Route gauge hoses away from belts, pulleys, and exhaust parts, and keep long hair, jewelry, and loose clothing away from belts.
• Before working under a tilted hood or cab, make sure its support is locked.
• Before working on an air-operated fan clutch or HVAC air controls, release the stored air pressure.