When “Hand-Off-Auto” Isn’t Really Auto: Hidden Override Traps
- Alex Khachaturian
- Oct 20
- 10 min read
Updated: Oct 21
Promise: Stop chasing phantom “Auto” modes. In 10 minutes, you’ll know exactly where hidden overrides live, and how to clear them safely and fast.
TL;DR
“Auto” lies whenever something upstream has a higher say (priority arrays, hardwired HOA, VFD Local, bypass mode, safeties, min/max clamps).
Start at the wire, then the drive, then the controller, then the network. Verify before you touch.
Build a repeatable HOA triage: Status → Source → Priority → Proof. Document clears, leave breadcrumbs.
Key Takeaways
Auto ≠ Authority. The ‘A’ on a switch only works when nothing above it is asserting control.
BACnet priority arrays decide winners. Anything at a higher priority than your program’s output wins every time.
Hardware beats software. HOA stations, VFD panels/bypass packages, safeties, and jumpers will trump trending logic.
Standardize the hunt. Same checks, same order, every call, your callback rate drops and your confidence spikes.
Bread crumbs = credibility. Photos + amps + PA clears + device IDs end debates.
Quick Links
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The Tiny Door, the Wasps, and the Six VFDs
Since day one I was stuck chasing and fixing forgotten “problems from the past.” It took some time but I eventually acclimated to the small “city” that is NASA’s Jet Propulsion Laboratory, and started exploring in my government issued golf cart. My target; Six failed VFDs in Building aptly labeled “building 279”. This place was full of forgotten rooms: boiler spaces behind repurposed blast doors, undercut tunnels in the hillside, Cold War-era fallout shelters exactly what you would expect them to look like. However, for a site that sends robots to other planets, the BAS left a lot to be desired. I made myself a promise: fix one thing at a time. Small good decisions would win!
One day I found a hatch in a wall, half-hidden by ductwork, guarded by a wasp nest. I squeezed through into a two-foot-wide, seven-foot-tall ring corridor that wrapped the entire building. Obviously this was where they were hiding the aliens.
As I ventured around seemingly endless corridors ducking under pipes and frayed insulation, I found what I was looking for. Buried in that mezzanine were six VFDs for fans that had been alarming on my console since day one, ignored, forgotten, still humming on and off since the 1950s. Graphics said Hand-Off-Auto: Auto. The building said otherwise.
A little knowledge, a little rewiring, and a little luck (which is just preparedness cashing its checks) later, I had the truth: several drives were sitting in Local, safeties were half-bypassed, and a couple of status proofs were never wired back. Clear the locals, fix the proof chain, return the drives to Remote/Auto, trend to verify, document the breadcrumbs. The “failed to start” ghost alarms I was told I would never fix don’t bother vanished.
What this taught me (and why it matters for ‘Hand-Off-Auto’):
Wire beats web. The VFD faceplate told the truth the graphic couldn’t.
Local vs Remote decides the winner. If the drive is in Local, your BAS is a spectator.
Proofs are part of control. No AUX/DP proof, no run, no matter what the command says.
Document the fix. Photos, amperage, priority clears, device IDs, leave breadcrumbs for the next tech (even if it’s you in six months).
Quick Win: 90-Second HOA Reality Check
Go physical first: Find the real devices, even if they’re in “impossible” spots (mezzanines, behind ductwork, ring corridors).
VFD truth test: Check the faceplate. If it says Local, your BAS is a spectator. Put it in Remote/Auto and confirm speed source.
Safeties & proof: Freezestat, smoke, HP/LP, door interlocks, closed? Does the AUX/DP proof make when commanded?
Match command to current: If BAS says RUN but clamp meter reads 0 A, the block is upstream. Keep walking.
You’ll catch most “Auto but dead” cases right here, exactly like those six VFDs.
Recommended Gear
Playbook: Restore True Auto (Hand-Off-Auto)
Outcome: Prove who’s really in control and return equipment to true Auto, safely, verifiably, and with clean documentation.
1) Start Physical: “Wire Beats Web”
Hidden access reality: Expect controls hardware in non-obvious locations (mezzanines, behind panels, ring corridors). Bring a headlamp and camera.
HOA station (panel/MCC): OFF, HAND, or AUTO? Photograph it.
VFD faceplate: Local vs Remote; speed source; run permissive; fault codes; min/max limits.
Bypass package state: Note DRIVE / BYPASS / OFF selector, lamp status, and which contactor is pulled in. Photograph before/after.
Safeties: Freezestat, smoke, HP/LP, door interlocks, test continuity if needed.
Manual valves/dampers: Tagged open/closed? End switches present and functional?
Jumpers & bypasses: Any “temporary” jumpers that became permanent? Tag and remove with permission.
2) Verify Power & Proof
Control power: 24 V or 120 V present where the output originates?
Aux/Proving: Many sequences require Proven On. If AUX is miswired, you’ll see start → dropout.
Interlocks: Exhaust fans, isolation dampers, or differential pressure proving may be gating your start.
3) Controller Reality Check
Output object: Is the BAS actually commanding ON (or a non-zero analog)?
Application limits: Minimum off time, post-purge, lockouts“not running yet” ≠ “never runs.”
Local HMI overrides: Some controllers have a local override that never made it back to graphics.
4) Network Truth (Where “Auto” Lies)
BACnet Priority Array: Read Priority_Array and Relinquish_Default. If a value exists at a higher priority than your program, your command is ignored.
Usual suspects: Manual_Operator writes (leftover forces), Schedules, Alarm/Reset actions, global clamping/load shed.
Schedules & holidays: Is an exception schedule active? Sunday holiday on a Tuesday will ruin your day.
Global strategies: Minimum speed floors, smoke sequences, freeze protection, or supervisory trims applied above the controller.
5) Graphics ≠ Ground Truth
Audit binding: Make sure the pretty tag points to the real object. Legacy jobs often bind new graphics to retired points.
Expose proof: If your graphic shows command only, add the Proven point side-by-side.
6) Prove the Fix
Command → Feedback → Proof: Start the fan, watch current rise, verify status closes.
Trend 15 minutes: Catch oscillations, lockouts, or min-off timers that a snapshot misses.
Remove forces: Clear to Null at higher priorities; confirm Relinquish_Default.
Document: Photos, amperage, PA slots cleared, device IDs, MACs, locations.
Bypass Drives 101: What, Why, and How They Hijack “Auto”
What a bypass drive is:
A VFD with a built-in bypass starter so the motor can run across-the-line (full speed) if the drive or its controls fail. The bypass package is a small power center: disconnect/fuses, contactors, overloads, and selector switches that let you choose DRIVE or BYPASS (and sometimes OFF).
Why they exist:
Keep-air-moving mission: Critical fans must run even if the VFD dies.
Service continuity: Keep the building occupied while you diagnose/replace a drive.
Life-safety/specs: Many designs require a drive-independent run path for smoke control or emergency modes.
How they behave:
Drive Mode: Normal VFD operation; BAS (or local pot) sets speed.
Auto Bypass: If the VFD faults, logic automatically transfers to an across-the-line starter at 60 Hz.
Manual Bypass: A human flips to BYPASS (often keyed). Motor runs full speed regardless of BAS speed commands.
Topologies:
2-Contactor bypass: Drive vs Bypass (mechanically interlocked).
3-Contactor bypass: Adds a Drive Isolation contactor for larger motors.
Both include overload protection and typically a separate HOA for bypass.
Authority changes:
In Drive, your speed command is king.
In Bypass, there is no speed control, your “30%” becomes start/stop permissive only. Proofs should still report, but retrofits can be messy.
Spot it fast:
Panel lamps/switch labels, which contactor is in, FLA-ish clamp current even at “30% command,” VFD keypad says “Bypass Active.”
Use it wisely:
Drive failed? Use bypass to keep air on. Don’t use it as a convenience to “get more air.” Energy and wear costs spike.
Commissioning tips:
Label modes plainly, trend “Bypass Active,” exercise Drive→Bypass→Drive transfer, and prove proofs in both paths.
Service pitfalls:
Don’t tune a PID while in bypass; always return selector to DRIVE and log it; verify smoke/fire interlocks hold in both paths.
When VFDs Wreck RS-485: Shielding, Grounding & the Scope Check
Your graphic says Auto, your program looks right, but the device ignores you, or replies once every few minutes. Before you rewrite code, check the wires. VFDs are noisy neighbors. Poor shielding/grounding around VFD output leads can spray common-mode and differential noise onto nearby RS-485 (BACnet MS/TP) trunks and make “Auto” look unresponsive.
What goes wrong
Parallel runs: RS-485 trunk laid in the same tray or conduit as VFD motor leads or line side, induced noise corrupts packets.
Floating shields: Shield/drain not bonded properly (or bonded at both ends creating ground loops).
Bad terminations/biasing: Missing 120 Ω ends or weak bias resistors make the bus more susceptible to noise.
Star topology & stubs: Tees and long drops reflect signals; noise exploits those reflections.
Unisolated interfaces: Non-isolated converters/controllers conduct drive hash straight into your laptop/tool.
How it looks on the BAS
Random offline/online flapping or rising “Retry Count.”
Commands that “don’t take” unless you spam them.
Stale priorities: You “cleared” a force, but the device never saw it. That’s how “Auto” lies without any malicious override.
Fast fixes that actually work
Separation: Keep RS-485 at least 12 in (300 mm) away from motor leads; cross at 90°.
Shielding: Use twisted pair with drain (e.g., 22AWG, foil shield). Bond shield at one end only (typically the controller or panel ground bar).
Termination & bias: 120 Ω at both physical ends; proper network-level bias (one location).
No stars: Daisy-chain the trunk; keep stubs < 12 in where possible.
Isolate: Use opto-isolated 485 adapters; add ferrites to noisy sections; avoid sharing VFD power with controls power.
Reroute: If a trunk shares a tray with VFD leads, move it. Cheap re-pulls beat endless “software” fixes.
Prove it with a scope (and why your PicoScope pays for itself)
In our deep dive “BAS Communication Wires: The Tool You Didn’t Know You Needed,” we show how to clip a PicoScope or portable scope across +/– and earth to see:
Differential pair quality (clean square-ish vs fuzzy).
Common-mode bursts when the VFD ramps.
Reflections from bad terminations.
If noise spikes align with VFD acceleration or PWM switching, you just found the villain. Capture a screenshot, add it to the WO, and reroute/terminate/bond accordingly.
Communication noise mimics overrides, you command “Auto,” but the device never hears you, or your Priority_Array writes don’t land. Clean the bus, then re-test your “Auto.”
Troubleshooting (Symptom → Cause → Fix)
Symptom: “Graphic shows Auto + Run, but fan is off.”
Cause: VFD set to Local or panel HOA not in Auto.
Fix: Set VFD to Remote/Auto; place HOA to Auto. Verify proof and amps.
Symptom: Fan ignores my speed command and sounds like a jet.
Cause: Bypass is active (manual or auto). Motor is across-the-line at 60 Hz.
Fix: Return selector to DRIVE, clear any drive faults, verify permissives, and retest. Trend Bypass Active.
Symptom: Command toggles on then drops.
Cause: Proof chain open (AUX not made, DP switch mis-set, freezestat open).
Fix: Verify interlocks; correct switch settings; restore proof input; re-enable sequence.
Symptom: Speed stuck at 40% no matter what.
Cause: Global minimum speed clamp or safety floor in supervisory logic.
Fix: Temporarily lower min floor for test; document reason; restore after validation.
Symptom: BAS shows 100% command; field reads 0–2 mA/0 V.
Cause: Analog output miswired or output forced elsewhere at a higher priority.
Fix: Check wiring/calibrate AO; clear Priority_Array writes; re-test.
Symptom: Device keeps going offline/online; commands don’t ‘stick.
Cause: RS-485 noise from nearby VFD leads; bad termination/bias; shield bonded wrong.
Fix: Separate trunk from VFD cabling; correct terminations; single-end shield bond; use isolated 485; verify with PicoScope.
Symptom: Heat never starts on schedule.
Cause: Holiday/exception schedule active; time sync mismatch.
Fix: Correct NTP/time source; remove wrong exception; verify with a test event.
Symptom: My force won’t clear.
Cause: Multiple writers at different priorities; you cleared 16, someone wrote at 8.
Fix: Null every active slot above program priority; coordinate with other systems.
FAQ
Does “Auto” always mean the BAS is driving?
No. “Auto” is a mode selection. The authority might be the VFD, a bypass, a safety chain, or a higher BACnet priority.
How do I know if a bypass panel is active?
Look for a BYPASS lamp or selector, listen/see which contactor is in, and compare amps to expected load. Full-speed sound at “30% command” = bypass.
Where do BACnet overrides hide?
In the Priority_Array. Anything at a higher slot than the application output wins. Clear to Null, don’t just write zeros.
Why does my fan show RUN but proof is false?
Some graphics show command status, not proof. Expose the Proven On point and fix the proof chain.
Can bad RS-485 wiring make Auto look broken?
Yes. Noise and reflections cause missed packets and stale writes. Fix shielding, terminations, and topology; verify with a scope.
Is trending necessary for HOA issues?
Yes, 10–15 minutes exposes lockouts, min-off timers, and schedule interactions that screenshots miss.
What if the client insists on a temporary bypass?
Document risk, set a clear revert plan with a time box, label any physical changes, and schedule a follow-up to remove the bypass.
Field Checklist (Print This)
□ Locate the hardware (mezzanines/hidden corridors/behind ductwork) and photograph access path
□ Panel/MCC HOA: OFF / HAND / AUTO (photo)
□ VFD: Remote/Auto, correct speed source, no faults (photo of faceplate)
□ Bypass package: Selector at DRIVE / BYPASS / OFF; lamps match; contactor positions photographed
□ Safeties: Freezestat, smoke, HP/LP, interlocks = closed
□ Proofs: Fan AUX / DP switch returns True when started
□ Controller Output: Commanded state matches sequence
□ Priority Array: All higher slots Null; program has authority
□ Schedules: Weekly + exceptions correct; controller/server time in sync
□ Amps vs Command: Clamp meter value matches expected state
□ RS-485 bus health: 120 Ω termination both ends; single-end shield bond; no stars; clear of VFD motor leads; optional quick scope capture
□ Trend 15 minutes; attach photos and notes (device IDs, MACs, locations)
□ Clear any forces; leave breadcrumbs in WO
Results & ROI
A standardized HOA Override Hunt typically:
Cuts average triage time from 60+ minutes to 15–20 minutes.
Reduces repeat truck rolls for the same complaint by 30–50%.
Prevents unnecessary parts/labor (e.g., motors/VFDs) and protects warranty claims.
Increases client trust, your documentation shows cause → fix → proof in one concise note.
Wrap-Up
One action tonight: Add two lines to your pocket HOA Override Hunt card, “Check Bypass selector” and “Scope the RS-485 if devices ignore commands.” Tomorrow, use it before you open the laptop.
The day I stopped trusting the “A” on the graphic, and started proving the real authority, was the day my callbacks dropped and my confidence spiked.
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