JL
HEATING
&
AIR
Field Diagnostic
Checklist
HVAC Field Diagnostic Checklist
Tap each item to check it off. Fill in job info, then hit Send.
Job Info
Tech Name
Date
Customer / Address
Unit #
Work Order #
Notes / Findings
❄️
No Cool
0 / 17
▾
Thermostat / Controls
Thermostat set to COOL, fan to AUTO
Set point is below current room temp
Check for blank screen or dead batteries
Power & Safety
Disconnect at outdoor unit is seated and ON
Breaker for condenser — not tripped
Breaker for air handler / furnace — not tripped
Float switch or secondary drain pan — tripped?
Indoor Unit
Indoor blower motor running? (feel vents for airflow)
Evaporator coil — iced over?
Filter — dirty / clogged?
TXV / metering device — check temps across it
Drain line — clogged causing float lockout?
Outdoor Unit
Condenser fan spinning?
Compressor humming / running?
Suction line cold and sweating?
Condenser coil — heavily fouled or blocked?
Visible ice on lines or coil?
TIP:
Check the filter and float switch first — clears the majority of no-cool calls before touching the refrigerant circuit.
🔥
No Heat
0 / 15
▾
Thermostat / Controls
Thermostat set to HEAT, fan to AUTO
Set point is above current room temp
Check for blank screen or dead batteries
Power & Safety
Breaker not tripped
Door safety switch on furnace fully engaged
Rollout switch or high limit — tripped / open?
Check error codes on furnace board (count LED flashes)
Gas Furnace
Gas supply valve open at furnace
Gas pressure in spec: 3.5" WC LP / 7" WC NG at manifold
Ignitor glowing? (hot surface ignitor)
Flame sensor — dirty? Check µA reading
Inducer motor running before ignition attempt?
Vent / flue — blocked, disconnected, or condensate backed up?
Heat Pump
Reversing valve shifting to heat mode?
Defrost board functioning? (check terminals)
Aux / emergency heat strips energizing when outdoor temps are low?
Check refrigerant pressures — low charge = poor heat output
TIP:
Count the LED flash code on the furnace board first — it will usually point you straight to the fault before any testing.
💨
Weak Airflow
0 / 12
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Filter & Coil
Filter — clogged? (most common cause)
Evaporator coil — iced over or heavily fouled?
Blower wheel — caked with dirt / debris?
Blower
Blower running at correct speed?
Blower capacitor — test with meter
Belt drive (older unit) — belt slipping or broken?
Blower motor amp draw in spec?
Ductwork
Supply plenum — any disconnected or collapsed duct?
Return air — single small return choking the system?
Flex duct — kinked, crushed, or over-long runs?
Dampers — manually closed or stuck?
Static Pressure
Measure total external static — above 0.5" WC is a red flag
Oversized coil or undersized duct for the equipment?
TIP:
A dirty filter causes weak airflow more than anything else. If static is over 0.5" WC, dig into the duct system.
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