Ambulance HVAC Troubleshooting: Blower Motors

Welcome back to our HVAC series! This post covers a variety of blower motor issues with their possible causes and solutions. For other basic maintenance and remedies, check out Ambulance HVAC Troubleshooting: Common Issues with Simple Fixes.

If the main unit blower motor is not operating…

Follow the troubleshooting protocol below. There a several possible causes. Here’s what to look for and how to address each issue.

Blown Circuit Breaker: Inspect the circuit breaker for evidence of a trip or damaged wires, then reset the breaker or repair any compromised wiring.
Broken Wiring or Bad Connection: Check that the fan motor is properly grounded, and connectors are intact. Repair or replace any wiring or connectors that are amiss.
Fan Motor Malfunction: Use a circuit tester to check the lead wires from the motor. If there is a negative reading, the wires will need to be replaced.
Broken Resistor Wiring: Use a circuit tester to check the resistor. If there is a negative reading, the wiring will need to be replaced.
Fan Motor Switch Malfunction: Operate the fan switches in sequence. If the fan does not operate, replace the motor switch.

If the blower motor operates normally, but there is little to no airflow…

Look into these four areas and make repairs and replacements as indicated.

Evaporator Inlet Obstruction: Check the blower inlet and remove any obstructions and clean the inlet.
Air Leak: Check the cooling unit case joints. Repair or adjust any joints that are loose or broken.
Defective Thermostat Switch (Frozen Evap): Use a circuit tester to check the thermostat switch and replace it if the switch is faulty.
Duct Hose is Off, Crushed, or Torn: Inspect the duct hose to ensure it’s securely attached and intact. If the hose is in good shape, reattach it. If the hose has minor tears, a repair may be sufficient. If there is significant damage, it’s best to replace the hose with a new one.