Field Notes
Air-handler freeze stat capillary and reset access record
Before winter operation release, the record should identify the air handler, coil boundary, freeze stat model, capillary placement, support and bend condition, setpoint, manual or automatic reset type, reset access, BAS alarm response, damper and valve response evidence, exceptions, and release decision.
Direct answer
Before an air handler is released for winter operation, the freeze stat record should identify the unit, coil or mixed-air boundary protected, freeze stat manufacturer and model, manual or automatic reset type, capillary length and routing, sensing-element location, support and bend condition, setpoint shown on the device or BAS, reset button access, label status, trip or simulated alarm evidence where allowed by the commissioning plan, fan, damper, valve, pump, and BAS response evidence, exceptions, witness, and release decision.
The record should prove that freeze protection was not accepted only because a device exists in the cabinet. It should show whether the capillary is actually where the coil can see cold air, whether it is supported without damage, whether the setpoint and reset type are known, and whether a technician can reach the reset safely after a trip.
Use this as documentation guidance only. The air-handler IOM, freeze-stat manual, controls sequence, commissioning plan, BAS standard, lockout rules, electrical safety plan, owner requirements, and qualified HVAC and controls technicians control placement, wiring, testing, reset, and winter operation.
Why this record matters
Freeze stat failures are rarely paperwork-only problems. A capillary left coiled in one corner, kinked at a support, hidden behind insulation, set without a record, or unreachable for reset can turn the first cold snap into nuisance trips or coil damage.
Manufacturer sources describe low-temperature cutout controls with vapor-filled capillary sensing elements, manual or automatic reset options, model-specific mounting guidance, and wiring or control limitations. NIH and ASHRAE G36-related material show that freeze protection is part of a broader air-handler response involving dampers, heating, alarms, and sometimes shutdown.
That is why the winter-release record should connect photos, settings, and controls response. A note that says freeze stat checked does not tell the owner whether the sensing element protects the coil face or whether the operator can reset the device after a cold alarm.
Define the unit and protected boundary
Start with the air-handler tag, location, serving area, coil type, outdoor-air path, mixed-air plenum, preheat coil, chilled-water coil, heating coil, damper section, BAS point names, freeze stat device tag, drawing reference, and winter operation release boundary.
Do not treat one freeze stat as evidence for every coil in the unit unless the drawings and control sequence say that is the intended boundary. Record whether the device protects a heating coil, cooling coil, mixed-air section, 100 percent outdoor-air unit, or another defined section.
If multiple freeze stats protect the same coil face, list each device separately so missing coverage does not hide behind one accepted device.
Photograph capillary placement
Photograph the full capillary run, not only the control box. The photo set should show the start point, end point, serpentine pattern where used, distance from coil or protected face as required by the project, horizontal or downstream location where applicable, supports, penetrations, insulation openings, access doors, and the relation to outdoor-air and return-air paths.
Johnson Controls, Carrier, ACI, Dynacon, Honeywell, and INTEC materials all support treating the sensing element as the core field condition, not a decoration near the coil. Some documents call for exposure to areas likely to encounter low temperature, avoidance of kinks, support, and model-specific reset and mounting requirements.
If photos cannot show the capillary because insulation, guards, or access panels block it, the record should say what was opened, what remains hidden, and who accepted the incomplete view.
Record supports, bends, and damage risk
The record should show whether the capillary is kinked, crushed, sharply bent, rubbing on sheet metal, unsupported, sagging into a drain pan, pulled tight at the case, tied to hot surfaces, or exposed to service damage.
Manufacturer instructions commonly warn against kinks, excessive force, and poor bends. Johnson A11/A70 installation material also shows detailed element support and bend guidance. The article does not replace that guidance; it requires photos clear enough for the qualified team to verify the actual installation.
If a support or bend does not match the manual or approved detail, mark the winter release held or released only with the approving authority and correction date.
Setpoint and reset type
Record the setpoint shown on the freeze stat or BAS, the approved setpoint from the controls sequence, whether the device is manual reset or automatic reset, differential or time delay where applicable, and the person who verified the value.
Sources reviewed show a range of products and settings, including manual reset low-temperature cutout controls, factory or adjustable trip values, and time-delay freeze-stat options. NIH guidance gives an example of typical freeze-stat setpoint context for 100 percent outdoor-air AHUs, while ASHRAE G36-related material describes staged freeze-protection responses based on supply-air temperature thresholds.
Do not set a value from this article. The record should show the actual value and the document that controls it.
Reset access and labeling
Photograph the reset access with the access door open and closed where safe and allowed. Show whether a technician can identify the freeze stat, reach the reset button, read the label, and reset without reaching through moving parts, energized compartments, blocked platforms, or sealed insulation.
Manual-reset devices are only useful if the team can find and reach them after a trip. The record should include label text, device tag, access panel tag, lockout or service note, and whether a ladder, platform, or tool is required.
If the reset is inside a control compartment, behind a panel that requires electrical access, or above a ceiling with no safe access path, record the access hold before winter release.
Trip, alarm, and response evidence
Where the commissioning plan allows a trip or simulated alarm, record the method used by qualified staff, device ID, trip or alarm time, BAS point, fan command, outdoor-air damper command, heating valve response, pump or heating request, alarm priority, manual reset status, and return-to-normal evidence.
NIH and ASHRAE G36-related material show that freeze protection often needs more than a local switch. Dampers, heating requests, alarms, and shutdown or staged response may be part of the accepted sequence.
If the sequence is not tested during the release window, record the reason, the previous test evidence used, and what condition must be met before winter operation.
BAS trend and outdoor-air context
Attach or reference a BAS trend showing relevant points before release: outdoor air temperature, mixed air temperature, supply air temperature, freeze stat status, outdoor-air damper command and feedback where available, heating valve command, fan status, and alarm status.
The trend should match the photo record. If the capillary is downstream of a coil but the BAS point names suggest a different section, resolve the mismatch before release.
For units with economizers, 100 percent outdoor-air operation, or known stratification risk, record the owner-approved winter mode and any restrictions on outdoor-air operation.
Release table
Use a compact table so operations, controls, TAB, commissioning, and service teams review the same evidence.
| Record field | What to capture | Why it matters |
|---|---|---|
| Unit boundary | AHU tag, coil, mixed-air section, BAS points, serving area | Defines what is being released |
| Device identity | Freeze stat tag, manufacturer, model, reset type, capillary length | Ties the record to the installed device |
| Capillary placement | Full run, serpentine pattern, protected face, access panels, hidden sections | Shows whether cold air can be sensed |
| Support and bends | Clips, brackets, bends, kinks, rubbing, sagging, penetrations | Protects the sensing element |
| Setpoint | Device value, sequence value, differential or time delay, verifier | Prevents undocumented adjustments |
| Reset access | Button location, label, access path, safety restriction, platform need | Shows the device can be restored safely |
| Sequence evidence | BAS alarm, fan, dampers, valves, heat request, reset, trend | Confirms the control response used for release |
| Decision | Release, release with restriction, hold, retest, owner | Defines winter operation status |
Before-release checklist
Run this checklist before winter operation release.
- AHU tag, coil boundary, serving area, and BAS point names are recorded.
- Freeze stat tag, manufacturer, model, reset type, and capillary length are recorded.
- Full capillary run is photographed from start to end.
- Sensing element placement is tied to the coil or mixed-air section it protects.
- Supports, bends, penetrations, insulation openings, and damage risks are photographed.
- Setpoint and controlling sequence value are recorded.
- Manual reset button or automatic reset status is documented.
- Reset access, label, access door, and service path are photographed.
- Trip, simulated alarm, or prior accepted test evidence is attached where required.
- BAS trend, damper response, valve response, fan status, alarm, exceptions, and release decision are recorded.
Weak versus strong record
Weak record: Freeze stat checked, set at 38 F, AHU ready for winter.
Strong record: AHU-4 serving Level 3 east was reviewed under winter release WR-31. Photos show freeze stat FZ-AHU4-1, Johnson low-limit control, manual reset, 20 ft capillary routed in a horizontal serpentine pattern across the downstream face of the preheat coil. Clips support the element at each bend and intermediate runs, with no kinks or rubbing at the casing penetration. Device setpoint photo shows 38 F, matching controls sequence CS-4 revision 7. Reset button is labeled inside access door AD-4-2 and reachable from the service platform without entering the fan section. BAS trend from 7:10 a.m. to 7:25 a.m. shows freeze alarm simulation accepted by the commissioning lead, fan command off, outdoor-air damper closed, heating valve command open, alarm received, and manual reset returned to normal. Release is approved for winter occupied mode only; economizer high-outdoor-air mode remains locked pending mixed-air stratification review.
The strong record ties device identity, placement, setpoint, reset access, BAS response, and release limits together.
Common mistakes
The most common mistake is photographing the control box while leaving the capillary hidden. The sensing element is the field condition that protects the coil.
Another mistake is recording only a setpoint without the controlling sequence, reset type, or access path. A manual-reset device behind a blocked access panel can still fail the release record.
Other mistakes include kinked capillary tubing, loose supports, capillary bunched in one corner, no photos at bends, unlabeled reset buttons, no BAS point names, no alarm evidence, no damper or valve response, and no retest rule after insulation or access panels are reworked.
When to hold winter release
Hold release if the capillary is hidden, kinked, unsupported, damaged, not routed across the protected face, installed where cold air cannot reasonably reach it, or missing from part of the coil face that needs protection.
Also hold if the setpoint is unknown, the reset type is unknown, the reset button is inaccessible, the BAS point cannot be matched to the device, the alarm does not report, the fan, damper, valve, or heating response does not match the sequence, or the commissioning plan requires a test that has not been accepted.
The hold note should name the AHU, freeze stat tag, missing evidence, correction owner, required retest or photo, and whether the unit can run in a restricted winter mode.
Owner handoff
The owner handoff should include capillary photos, device label photos, setpoint photo, sequence reference, BAS trend, reset access photo, alarm receipt, fan/damper/valve response evidence, exceptions, winter mode restrictions, and retest triggers.
Keep the record with commissioning files, controls submittals, BAS graphics, TAB reports, O&M manuals, seasonal startup reports, and preventive maintenance records.
If insulation, access doors, coil sections, dampers, or control wiring are changed later, the record should define who reopens the release.
Questions before winter operation
Which coil or mixed-air section does this freeze stat protect? Where is the entire sensing element? What value is it set to, and what sequence requires that value?
Can a technician reach the reset safely after a trip? What BAS alarm appears? What fan, damper, valve, pump, and heating requests happen when the device trips or the alarm is simulated?
What condition cancels the release and forces retest?
Compliance and safety limits
This article does not select a freeze stat, set a trip value, route capillary tubing, test a safety circuit, reset a manual-reset device, authorize winter operation, or replace commissioning. It is a record structure for preserving placement, setpoint, reset access, sequence, exception, and release evidence.
The air-handler manual, freeze-stat instructions, BAS sequence, commissioning plan, electrical safety controls, lockout rules, owner standards, and qualified HVAC and controls technicians control the work. If those documents conflict with this checklist, use the controlling requirement and record the decision.
Do not enter fan sections, open energized compartments, move capillary tubing, simulate alarms, reset safety devices, or override controls outside qualified authority.
Sources checked
- Johnson Controls, A70 Series Low and High Temperature Limit ControlsUsed for low-temperature limit control, manual reset, mounting, and capillary placement context.
- Johnson Controls, A11 Series Low Temperature Cutout Control InstallationUsed for sensing element support, bend, placement, and access detail context.
- Carrier, Freeze Stats Installation and OperationUsed for vapor-charged capillary, manual/automatic reset, and low-temperature cutout context.
- Automation Components, Freeze Stats Series InstallationUsed for HVAC freeze-stat application, setpoint, reset, and capillary context.
- DynaCon, 2xSPDT Freezestat Installation GuideUsed for capillary handling, serpentine placement, downstream coil location, and support context.
- Honeywell Building Automation, A/FLS Series Freeze StatUsed for vapor-charged capillary and low-temperature cutout application context.
- INTEC Controls, Low-Temperature Cut-Out Capillary ThermostatsUsed for low-temperature cutout thermostat, capillary length, reset, and setpoint context.
- Trane Technologies, Outdoor Air Handling Units CatalogUsed for time-delay freeze-stat option and setpoint-range context.
- NIH ORF, Heating and Cooling Coil Freeze Protection DesignUsed for 100 percent outside-air AHU freeze-protection placement, distribution, reset, and sequence context.
- Trane Support, Freeze Stat GRAAUsed for freeze-stat sensing element location, temperature, and time-dial context.
- LBNL, ASHRAE G36 AHU Freeze Protection Sequence ReferenceUsed for staged AHU freeze-protection sequence and alarm response context.
- Johnson Controls, A70 Series Temperature Controls for Trane ApplicationsUsed for coil freeze detection and HVAC application context.
- Trane, Performance Climate Changer Air Handler IOMUsed for air-handler controls, safety, and service context.