Floating Point · 3-Wire · No Spring Return
HAC-34
HAC-34
Belimo CMB24-3-T
Inline Damper
3-Wire Open / Stop / Close · 24 Vac/dc · DDC Floating Point · 6"–20"
- ✓3-wire floating point — Open / Stop / Close incremental positioning
- ✓No spring return — holds last blade position on power loss
- ✓24 Vac or 24 Vdc supply voltage
- ✓End switch available on all sizes for BAS position confirmation
- ✓Heat bypass (−H) available on all sizes — confirm pricing with wholesaler
- ✓Compatible with Johnson Controls, Siemens, Honeywell, Automated Logic, and other BAS platforms with floating point outputs
- ✓Factory-mounted Belimo CMB24-3-T — ships ready to install
Is this the right product?
✔ Right product if
Your DDC controller has a 3-wire floating point output (Open / Stop / Close) and needs incremental blade positioning on a fresh air, ventilation, or zone damper in sizes 6"–20".
✗ Not this product if
On/off 2-wire control → use HAC-40 (TFB24)
Analog 2–10 VDC → use HAC-43 (TFB24-SR-T)
Spring return fail-safe required → CMB24-3-T holds last position. Use HAC-40 (on/off) or HAC-43 (modulating).
Analog 2–10 VDC → use HAC-43 (TFB24-SR-T)
Spring return fail-safe required → CMB24-3-T holds last position. Use HAC-40 (on/off) or HAC-43 (modulating).
What It Does
3-wire Open / Stop / Close. DDC floating point output. Holds last position on power loss — no spring return.
NO SPRING RETURN — Blade Holds Last Position on Power Loss
The CMB24-3-T has no spring return. On power loss the blade stays wherever it was — it does not move to a defined open or closed fail-safe position. If your application requires the damper to seal or open on power loss, use a spring return product: HAC-40 (TFB24) for on/off, or HAC-43 (TFB24-SR-T) for modulating.
The HAC-34 pairs Hoyme's inline damper body with the Belimo CMB24-3-T 3-wire floating point actuator. Three control wires — Open, Stop, Close — give the DDC controller direct incremental positioning of the damper blade. While the Open wire is energized, the blade moves toward open. While the Close wire is energized, the blade moves toward closed. When neither is energized, the blade holds its current position.
3-Wire Control — How It Works
OPEN
Energized → blade moves toward open while wire is energized
CLOSE
Energized → blade moves toward closed while wire is energized
STOP
Neither energized → blade holds current position
How floating point differs from analog (2–10 VDC): Analog tracking is continuous — the actuator follows the signal level directly. Floating point is incremental — the DDC controller pulses the Open or Close wire for a timed duration to move the blade a proportional amount, and builds a model of blade position from cumulative pulse time. Which one the system uses depends on the DDC output card, not the damper. The HAC-34 is the product when the DDC has floating point outputs (Open/Close terminal pair) assigned to the damper. If the DDC uses 2–10 VDC analog outputs, use the HAC-43 (TFB24-SR-T).
Belimo Series — Control Type Selector
All Belimo-actuated HAC variants on a single Hoyme inline damper body. Select by control type and voltage.
| Model | Actuator | Control Type | Voltage | Spring Return | Link |
|---|---|---|---|---|---|
| HAC-40 | TFB24 | On/Off | 24 Vac/dc | Yes | View |
| HAC-44 | TFB120 | On/Off | 100–240 Vac | Yes | View |
| HAC-43 | TFB24-SR-T | Modulating 2–10 VDC | 24 Vac/dc | Yes | View |
| HAC-60 | LMB24-SR-T | Modulating 2–10 VDC | 24 Vac/dc | No — holds last | View |
| HAC-34 ← You are here | CMB24-3-T | Floating point 3-wire | 24 Vac/dc | No — holds last | — |
| HAC-30 | LMB24-3-T | Floating point 3-wire | 24 Vac/dc | No — holds last | View |
| HAC-35 | CMB120-3 | Floating point 3-wire | 100–230 Vac | No — holds last | View |
| HAC-70 | LMX120-3 | Floating point 3-wire | 100–230 Vac | No — holds last | View |
| HAC-90 | FSLF24 US | Fire & Smoke (UL 555S) | 24 Vac | Yes | View |
| HAC-80 | FSLF120 US | Fire & Smoke (UL 555S) | 120 Vac | Yes | View |
Configuration Guide
Select size, end switch, and heat bypass. Confirm 3-wire terminal assignments with the DDC controls designer before wiring.
| Variant Code | End Switch | Heat Bypass | Part Number Example (10") |
|---|---|---|---|
| OPP | No end switch | No bypass | HAC-1034-OPP |
| OPP-H | No end switch | 10% bypass | HAC-1034-OPP-H |
| SPP | End switch included | No bypass | HAC-1034-SPP |
| SPP-H | End switch included | 10% bypass | HAC-1034-SPP-H |
−H Pricing Anomaly — Confirm Before Ordering: The −H heat bypass variants are priced lower than the standard (non-bypass) variants at each size. This is unusual. Confirm with your wholesaler or Hoyme directly that the correct variant is being selected. Do not assume −H is always the lower-cost option — the price difference may reflect a blade configuration rather than a conventional add-on.
−H Heat Bypass — Hot Air Zone Control Only: Do not specify −H on fresh air intake, make-up air, or ventilation applications. The 10% bypass allows continuous outdoor air infiltration when the damper is commanded closed. Specify −H only on hot air supply duct zone control applications.
Part Number Decoder
HAC-1434-SPP
HAC
Product family: universal inline air control damper
14
Size (2-digit): 06=6", 08=8", 10=10", 12=12", 14=14", 16=16", 18=18", 20=20"
34
Motor code: Belimo CMB24-3-T, 3-wire floating point, 24 Vac/dc, no spring return
O / S
End switch: O = no end switch | S = end switch included
PP
Floating point action code for CMB24-3-T 3-wire architecture
-H
Optional: 10% heat bypass. Hot air zone control only. Confirm pricing with wholesaler.
Key Specs
Sizes
6", 8", 10", 12", 14", 16", 18", 20"
Actuator
Belimo CMB24-3-T
Control Wires
3-wire: Open / Stop / Close
Supply Voltage
24 Vac or 24 Vdc
Fail-Safe
Holds last position — no spring return
End Switch
Optional (S prefix)
Relay
Not available
Heat Bypass
Optional (−H) — confirm pricing
CSA Status
Confirm with Hoyme
Warranty
2-yr electrical / 10-yr mechanical
Common Questions from the Counter
Answers to what comes up most when specifying the HAC-34.
What's the difference between floating point and on/off — and how do I know which one my DDC uses?
On/off uses 2 wires: one wire energized opens (or closes) the damper, wire de-energized springs to fail-safe. Floating point uses 3 wires: one wire moves the blade toward open while energized, a second moves the blade toward closed while energized, and when neither is energized the blade holds its position. Check your DDC output card spec — if the card has terminal pairs labeled Open/Close (or CW/CCW) that pulse to position the actuator incrementally, that's floating point. If it has a single switched output, that's on/off. If it has a 0–10 VDC analog output, that's modulating.
What happens to the damper blade on power loss?
The blade holds its last position — wherever it was when power went out. The CMB24-3-T has no spring return. If the damper was 40% open when power failed, it stays at 40% open. If this is not acceptable, use a spring return actuator: HAC-40 (TFB24) for on/off spring return, or HAC-43 (TFB24-SR-T) for modulating spring return.
Why is the −H heat bypass variant priced lower than standard at some sizes?
This is a pricing anomaly worth confirming with your wholesaler or Hoyme directly before ordering. The −H suffix indicates the 10% heat bypass blade configuration. The price difference may reflect a blade material or configuration difference rather than a conventional add-on pricing structure. Do not assume −H is always the lower-cost option — confirm the correct variant for your application before ordering.
Does the end switch help with position accuracy on a floating point system?
Yes, in a specific way. Floating point DDC controllers infer blade position from the cumulative time they've spent pulsing Open or Close — it's a model of position, not a direct measurement. Over time, if a pulse is missed or the actuator slips, the controller's model can drift from actual position. The end switch provides a definitive position confirmation at the fully open or fully closed position — when the end switch closes, the DDC knows with certainty where the blade is and can recalibrate its position model.
Can I use the HAC-34 on a fresh air intake application?
Yes — for the standard (non-H) variant on a fresh air intake where the DDC uses floating point outputs and holds-last-position on power loss is acceptable for the application. Confirm with the mechanical engineer that the holds-last-position behavior is acceptable for the specific fresh air intake design. If the damper must close and seal on power loss, use a spring return product instead.
Ready to Order
HAC-34 — Belimo CMB24-3-T Inline Damper
Select your size, end switch (OPP/SPP), and heat bypass option — then add to cart. Confirm −H pricing with your wholesaler before ordering.
Configure & Order →
Size · End Switch · Heat Bypass
Need help specifying the HAC-34?
Technical support available through your Hoyme wholesaler or direct.