Honeywell T991A1012 Proportional Temperature Controller

Product Description

The HONEYWELL T991A1012 is a proportional temperature controller designed for precise modulating control in HVAC and building automation applications. It uses a capillary-and-bulb sensing element to detect temperature changes and modulate a controlled device output in proportion to the deviation from setpoint rather than switching fully on or off. This proportional action reduces temperature swings and improves system stability. The unit features a 4.1875-inch bulb length and a 20-foot capillary, giving technicians flexible placement of the sensing element relative to the controller body. Licensed HVAC technicians and building automation specialists are the primary installers.

The T991A1012 is suited for residential and light commercial HVAC systems where proportional temperature control is preferred over simple two-position switching. Typical applications include duct-mounted or immersion sensing in air handling units, fan coil units, and similar hydronic or forced-air systems. The 20-foot capillary allows the sensing bulb to be positioned at a remote location while the controller body mounts in an accessible panel or wall enclosure.

Key Features

• Proportional control action minimizes temperature overshoot and reduces cycling
• 4.1875-inch sensing bulb length for reliable thermal response
• 20-foot capillary allows remote bulb placement away from the controller body
• Capillary-and-bulb sensing element eliminates need for separate temperature sensor wiring
• Compact form factor suitable for panel or enclosure mounting

Compatibility

Designed as an OEM-style proportional temperature controller for use in residential and light commercial HVAC systems requiring capillary-bulb modulating control.

Installation Notes

Installation should be performed by a licensed HVAC technician familiar with low-voltage control circuits and local mechanical codes. Disconnect and lock out all power to the system before wiring or mounting the controller. Route the capillary carefully to avoid sharp bends, kinks, or contact with hot surfaces that could damage the sensing element or affect calibration. Verify the sensing bulb is fully inserted and secured in the sensing well or duct fitting before restoring power and commissioning the control loop.