I85PREP
⌘ K
Red Seal RV Service Technician study materials
Red Seal RV Service Technician study resources

Red Seal RV Service Technician: Heating, Ventilation, and Air Conditioning

Red Seal RV Service Technician · Work through your exam, one topic at a time.

All guide sections

Heating, Ventilation, and Air Conditioning

HVAC items cover rooftop air conditioners, heat pumps, DSI furnaces, thermostats, and ducting. The exam wants you to read pressures, temperatures, and amp draws as evidence, and to follow the furnace ignition sequence in order rather than guessing.

Air conditioning

  • Rooftop units are sealed systems using R-410A, with older units on R-22. Charge by weight or by superheat and subcool, never by feel.
  • Compare compressor amp draw to the nameplate RLA. A weak run capacitor raises amps and can prevent starting.
  • Delta T, the difference between return and supply air, is normally 15 to 20 degrees F at about 80 degrees F ambient and 50 percent RH. Low delta T points to airflow or charge problems; unusually high delta T points to low airflow.
  • Charging indoors requires an indoor ambient in the 70 to 95 degree F range.

Heating

  • DSI furnace sequence: thermostat calls, blower purges, sail switch proves airflow, igniter lights, flame is sensed, gas valve stays open, and high-limit and thermal cutout switches act as safety backstops.
  • Because the sail switch is in series ahead of the valve, a blower that never reaches proving speed means the valve never opens. That single chain solves most no-heat calls.
  • Heat pumps use a reversing valve, defrost control, and backup heat strips; below roughly 35 degrees F the strips carry the load.

Thermostats and ducting

  • Common colours are R for 24 V hot, Y for cool, G for fan, W for heat, and B or O for the reversing valve. Confirm against the wiring diagram before trusting colour.
  • Crushed, disconnected, or undersized ducts kill airflow. Check the filter and registers before condemning the unit.

Worked example

An R-410A unit shows 55 degrees F suction line temperature at 68 psig suction pressure. R-410A at 68 psig saturates near 40 degrees F, so superheat equals 55 minus 40, or 15 degrees F. For a fixed-orifice RV unit, 10 to 15 degrees F is acceptable, so this sits at the top of the range. Confirm indoor ambient and airflow before adding refrigerant; a dirty evaporator can mimic an undercharge.

Traps

  • Topping off a sealed system instead of finding and repairing the leak.
  • Swapping a sail switch for a limit switch because both are in the same circuit.
  • Ignoring a clogged filter when delta T is low.
  • Mixing refrigerant blends or topping R-410A with an incompatible product.