Troubleshooting Matrix

From Chapter 39 of BAS Field Fundamentals: A Field Guide for the New Technician

BAS Field Referencebasfieldreference.com

Symptom → where to start

Symptom	Start here
No BAS value at all	Network, controller, wiring, sensor power
BAS value present but incorrect	Sensor, input scaling and type, wiring, terminal
Value correct at the device, wrong on the graphic	Wiring, terminal assignment, scaling, point mapping
Command present, equipment off	Output, interface device, safety string, electrical path, equipment
Command absent when it should be present	Sequence, mode, setpoint, schedule, override, lockout
Feedback disagrees with command	Sensor, wiring, interface, mechanical position
Actuator says 100%, result is wrong	Physical actuator, coupling, linkage, damper or valve, mechanical restriction
VFD fault	Fault history first, then mechanical load, then parameters
Equipment runs but produces no result	Mechanical: flow, rotation, belt, coil, capacity
Multiple zones affected at once	Stop at the zones. Upstream air handler, static pressure, supply temperature, plant
One zone affected, neighbours fine	That box, that room, that sensor
Loop oscillates	Sensor noise, actuator stroke time, mechanical binding — tuning last
Loop never reaches setpoint	Capacity, then authority, then integral action
Alarm firing but nothing is wrong	Threshold, time delay, deadband, suppression logic
Works in HAND, not in AUTO	Control path: output, interface relay, safeties, mode, override
Intermittent, cannot reproduce	Trend it and come back. Do not guess
BAS looks entirely normal, building does not	Go verify physically. The graphic is the last thing to trust

BAS software → Controller → Signal → Interface device → Electrical circuit → Mechanical equipment → Physical result

Identify the layer first. Half-split within it second. Test third.

Is it in AUTO? HOA switches, drive keypad mode, software auto/manual.
Is there an override? At any priority, from any source, placed by anyone.
What mode is it in? Occupied, unoccupied, warm-up, emergency, holiday schedule.
Are the neighbours affected? One or many decides whether you work here or upstream.
Has anything changed? Renovation, power event, controller swap, another contractor.
Is anything alarming that you have not read? Including recently cleared.
Does the trend show when it started? A start time is a huge clue.

Every one of those is free and takes seconds. Together they resolve or redirect a large share of calls before a tool comes out of the bag.