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Honeywell T775 Series 2000 Selection Guide | Memphis Control Center
Selection Guide

Honeywell T775 Series 2000 Selection Guide:
The Right Model, Spec'd in 5 Steps

The T775 replaced 38 older Series 1000 models — including the now-obsolete T991A. This guide walks you through every model, every key spec, and the full T991A cross-reference so you can find your replacement fast.

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Honeywell T775 Series 2000 Electronic Stand-Alone Temperature Controller
Graphical LCD w/ backlight
Intuitive keypad + lockout
NEMA 1 or NEMA 4X enclosure
24 / 120 / 240 Vac — any voltage
PI / PID modulating control
T775 Series 2000 Replaces T991A & 37 other models

What Is the Honeywell T775 Series 2000?

The T775 Series 2000 is Honeywell's current-generation electronic stand-alone temperature controller for commercial HVAC, boiler, chiller, agricultural, and process applications. It senses temperature remotely via a wired PTC sensor and provides switched relay outputs, modulating analog outputs (0–10 Vdc, 2–10 Vdc, 4–20 mA, Series 90), or floating outputs to control dampers, valves, pumps, compressors, and other loads.

Fourteen T775 models replace 38 older Series 1000 controllers — including every T991A variant. If you're looking at a T991A right now, it's discontinued. The T775 is what you need.

Important — operating control only: The T775 is an operating control, not a limit or safety control. If your application requires a safety or limit function, a separate listed safety device is required in addition to the T775.

All T775 controllers are field-mountable in any orientation on a panel or wall. Power options are 24, 120, or 240 Vac (50/60 Hz). Every model includes a digital input for setback or disable, a built-in time clock scheduler with two settable periods per day, keypad lockout, sensor calibration, and configurable minimum off time.

How to Select the Right T775 Model

The T775 family branches into standard models (A, B, M, R) and special-application models (L, P, U, S). Answer these five questions and the right model falls out.

1

On/Off or Modulating Control?

Relay-only models (T775A, T775B) switch loads on and off based on a setpoint. Modulating models (T775M, T775R with mod outputs) provide 0–10 Vdc, 2–10 Vdc, 4–20 mA, Series 90, or floating outputs for proportional control of valves, dampers, and actuators. Most boiler and chiller valve applications need modulating output.

On/Off → T775A or T775BModulating → T775M or T775R
2

How Many Relay Outputs Do You Need?

T775 relay models range from 1 to 4 SPDT relays per base unit. The T775L and T775P can expand to 8 or 12 stages total using T775S expansion modules. Count your loads: each compressor stage, pump, boiler stage, or fan requires one relay output.

1 relay2 relays4 relaysUp to 12 stages (with T775S)
3

Do You Need Outdoor Reset?

Reset models (T775R, T775P, T775L, T775U) automatically adjust the control setpoint based on outdoor temperature — as it gets colder outside, the hot water supply setpoint rises. This is standard on boiler reset applications. If you need reset, you must use a reset-capable model and a second sensor for outdoor air temperature.

No reset → T775A, T775B, T775MReset required → T775R, T775P, T775L
4

Special Application — Boiler, Sequencer, or Universal?

Three special models cover unique use cases: T775P for multi-stage boiler control with pump output and reset; T775L for staged sequencing of chillers and multi-compressor systems; T775U for non-temperature inputs like pressure or humidity via 0–10 Vdc or 4–20 mA sensors. If none of these apply, stay with the standard A/B/M/R models.

Multi-stage boiler → T775PChiller/compressor sequencing → T775LPressure or humidity control → T775U
5

Indoor or Washdown/Wet Environment?

Most T775 models are NEMA 1 (indoor, dry). Four models (T775B2016, T775B2024, T775M2014, T775M2022) are available in NEMA 4X enclosures rated for washdown, animal confinement, pool equipment rooms, and other wet or corrosive environments. NEMA 4X models ship with the T775-SENS-WR water-resistant sensor instead of the standard sensor.

NEMA 1 — standard indoorNEMA 4X — washdown / wet

Have Your Answers? Let's Find Your Part Number.

Tell us your application, number of stages, whether you need reset, and your voltage — we'll get you to the right T775 part number fast.

Get Expert HelpCall (901) 458-2000

T775 Model Breakdown — Every Series Explained

Once you've answered the five questions, here's what each model delivers.

Standard On/Off · Entry Level
T775A Series
Single-relay on/off controller
On/Off1 RelayNEMA 1

The T775A2009 is the simplest T775 — one SPDT relay output, one sensor input, standard NEMA 1 enclosure. It handles basic on/off temperature control for single loads like fans, pumps, or heating/cooling equipment where one setpoint controls one output. If your old T775A1001 needs replacing, this is the direct successor.

Choose the T775A when: You need simple on/off control with a single relay and single sensor, your application doesn't require modulating output or multiple stages, and NEMA 1 indoor mounting is acceptable.

T775A2009
1 SPDT
1
None
No
NEMA 1
Need a T775A2009?Request a Quote →
Standard On/Off · Multi-Relay
T775B Series
2- or 4-relay on/off controller
On/Off2 or 4 RelaysNEMA 1 & NEMA 4X

The T775B series expands the relay count to 2 or 4 SPDT outputs and adds a second sensor input. This covers multi-stage cooling towers, dual-compressor systems, two-stage heating/cooling, or any application requiring multiple switched outputs from a single controller. Four T775B models give you NEMA 1 or NEMA 4X in 2-relay or 4-relay configurations.

The T775B also supports a floating output option (eliminates two SPDT relays, used to drive floating actuators directly). Sensor B can serve as a high/low modulating limit reference on select configurations.

Choose the T775B when: You need 2–4 relay outputs for on/off staging, want NEMA 4X for wet or washdown environments, or are running a multi-stage cooling or heating system without modulating output.

T775B2016 / 2024 / 2032 / 2040
2 or 4 SPDT
2
None
No
NEMA 1 or NEMA 4X
Need a T775B model?Request a Quote →
Modulating Output · Most Specified
T775M Series
Analog modulating controller — direct T991A replacement
Modulating0–10 Vdc / 4–20 mAT991A ReplacementNEMA 1 & 4X

The T775M series is the workhorse modulating controller and the most common T991A replacement. It provides up to two independent analog outputs configurable for 0–10 Vdc, 2–10 Vdc, 4–20 mA, or Series 90 — plus up to 4 SPDT relay outputs depending on configuration. The T775M2006 (2 analog outputs, no relays, NEMA 1) is the standard direct drop-in for most T991A applications.

PI and PID control is standard on all modulating outputs, with configurable integral and derivative times and anti-integral wind-up. The modulating high/low limit feature lets Sensor A control output while Sensor B acts as a high or low limit guard — useful for freeze protection or overheat cutback on a secondary loop.

NEMA 4X variants (T775M2014, T775M2022) are available for washdown or outdoor cabinet installations.

Choose the T775M when: Your application requires proportional control of a valve, damper, or actuator via an analog signal; you're replacing a T991A; or you need PI/PID control with up to two independent modulating outputs.

T775M2006 / 2014 / 2022 / 2030 / 2048
0, 2, or 4 SPDT
Up to 2
0–10 Vdc, 2–10 Vdc, 4–20 mA, Series 90
PI / PID standard
NEMA 1 or NEMA 4X
Replacing a T991A? T775M2006 is usually the answer.Request a Quote →
Reset Option · Hot Water & Chilled Water
T775R Series
Outdoor reset controller
ResetHot Water / Chilled WaterNEMA 1

The T775R series adds outdoor reset to the standard T775 platform. Reset programming requires only four values: high and low control temperatures, and the corresponding high and low outdoor temperatures. As the outdoor temperature drops, the hot water setpoint automatically rises — saving energy by delivering only the supply temperature the building actually needs.

Five T775R models cover 2 or 4 relays, 0 or 2 analog outputs, and combinations thereof. All include two sensor inputs and reset as standard. The T775R is also used for chilled water reset — the inverse logic (as outdoor temp rises, chilled water setpoint drops) is simply the cooling mode configuration.

Choose the T775R when: Your application is hot water or chilled water reset, you're controlling a boiler or chiller with outdoor air compensation, or energy codes require supply water temperature reset.

T775R2001 / 2019 / 2027 / 2035 / 2043
0, 2, or 4 SPDT
0 or 2
2 (control + outdoor)
Yes — standard
NEMA 1
Hot water or chilled water reset? T775R is your model.Request a Quote →
Special — Multi-Stage Boiler Control
T775P2003
Boiler model with staged outputs, pump, and reset
BoilerMulti-StagePump OutputReset

The T775P2003 is purpose-built for multi-stage boiler systems. It provides 4 SPDT relay outputs (expandable to 8 or 12 with T775S modules), a dedicated pump output using the last relay, outdoor reset, and three sensor inputs (supply, return, and outdoor). Stage sequencing options include standard, first-on/first-off, or equal run time — protecting boilers from short-cycling and balancing wear across multiple units.

The T775P also includes a Digital Output alarm (low voltage) configurable for minimum, maximum, or differential temperature trips — the only base T775 model with this feature.

Choose the T775P when: You're controlling a multi-stage boiler system with a primary pump, need outdoor reset, want equal run time or first-on/first-off staging, or need built-in alarm output capability.

T775P2003
4 SPDT (+ pump output)
8 or 12 stages (T775S)
3 (supply, return, OAT)
Yes — digital low-voltage
NEMA 1
Multi-stage boiler application? T775P2003 is built for it.Request a Quote →
Special — Staged Sequencing
T775L2007
Chiller / compressor stage sequencer with reset
SequencerChiller / CompressorReset

The T775L2007 sequences multiple relay stages across one or two independent setpoints — ideal for multi-compressor chiller systems, reciprocating chiller control, or any application where you need to stage multiple loads with independently configurable heat and cool setpoints. Stage distribution between the two setpoints is freely programmable (e.g., 3 heat / 4 cool, 5 heat / 1 cool).

Up to two T775S expansion modules can be added for a total of 12 staged relay outputs. Two additional relays are available for independent on/off control if not consumed by the staged loops. Outdoor reset is included standard.

Choose the T775L when: You're sequencing multiple chiller compressor stages, need two independent heat/cool setpoints on the same system, or require up to 12 stages with flexible distribution.

T775L2007
4 base (up to 12 w/ T775S)
2 independent staged loops
Up to 2
Yes
NEMA 1
Sequencing a multi-compressor chiller? T775L2007.Request a Quote →
Special — Universal / Non-Temperature Input
T775U2006
Pressure, humidity, CO₂, or any analog input
UniversalPressure / Humidity0–10 Vdc / 4–20 mA

The T775U2006 accepts 0–10 Vdc or 4–20 mA sensor input for any process variable — pressure, humidity, CO₂, or any medium with an analog output. Compatible sensors include Honeywell H7625/H7635/H7655 humidity sensors, P7640A differential pressure transducers, and C7232/C7632 CO₂ sensors. Sensor B accepts a standard temperature input only (for reset applications).

Input range is configurable for pressure (up to ±500 PSI, ±30 in. w.c., ±3,000 Pa or kPa), humidity (0–100% RH), or temperature. This is the only T775 model that replaces the older H775 humidity and pressure controller line.

Choose the T775U when: Your controlled variable is pressure, humidity, or CO₂ rather than temperature, or you need a single controller to handle non-standard analog sensor inputs.

T775U2006
2 SPDT
2
0–10 Vdc or 4–20 mA
Temperature (PTC) only
NEMA 1
Pressure or humidity control? T775U2006.Request a Quote →
Expansion Module
T775S2008
4-relay expansion module for T775L and T775P
Expansion Only4 RelaysT775L / T775P Only

The T775S2008 is a 4-relay expansion module used only with the T775L or T775P base controllers. Up to two T775S modules can be added to bring total staged relay outputs to 8 (one T775S) or 12 (two T775S). The T775S has no standalone functionality — it only works wired to a T775L or T775P via the bus terminals.

Choose the T775S when: Your T775P boiler system exceeds 4 stages, or your T775L chiller sequencer needs more than 4 relay outputs.

T775S2008
4 SPDT per module
2 (per T775L or T775P)
No — expansion only
T775L2007, T775P2003
NEMA 1
Need more than 4 stages on a T775P or T775L?Request a Quote →

T775 Series Comparison at a Glance

Use this table to quickly confirm which model fits your application. NEMA 4X options are noted separately — all others are NEMA 1.

Honeywell T775 Series 2000 Model Comparison
FeatureT775AT775BT775MT775RT775PT775LT775U
Primary UseBasic on/offMulti-relay on/offModulating controlReset + mod/relayMulti-stage boilerChiller sequencingPressure / humidity
Relay Outputs12 or 40, 2, or 40, 2, or 44 (+pump)42
Analog OutputsNoneNoneUp to 20 or 2NoneNone2
Outdoor Reset✗✗✗✓✓✓✓
Expandable (T775S)✗✗✗✗✓ to 12✓ to 12✗
Alarm Output (DO)✗✗✗✗✓✗✗
Non-Temp Sensor✗✗✗✗✗✗✓ (4–20mA / 0–10V)
NEMA 4X Option✗✓✓✗✗✗✗
T991A Replacement——✓ PrimarySome models———
Sensor Inputs1222322

T991A to T775 Cross-Reference

The T991A is fully discontinued. Below are the confirmed Honeywell replacements. If your T991A model number isn't listed, call us — we'll look it up against the official cross-reference.

T991A obsolete to T775 replacement cross-reference
Obsolete ModelDescriptionT775 Replacement
T991A1012Proportional temp controller, 55–175°F, 5 ft capillary, Series 90T775M2006
T991A1061Proportional temp controller, 55–175°F, Series 90, 5 ft capillaryT775M2006
T991A1079Proportional temp controller, 55–175°F, Series 90T775M2006
T991A1194Proportional temp controller, 55–175°F, 5 ft capillaryT775M2006
T991A1244Proportional temp controller, 55–175°F, 5 ft capillaryT775M2006
T991A1350Proportional temp controller, 24' copper averaging elementT775M2006
T991A1764Proportional temp controller, Series 90 outputT775M2006

Note on Series 90 output: T991A controllers with a 135-ohm Series 90 potentiometer output connect to Series 90 actuators. The T775M supports Series 90 output — you will need the included 340-ohm resistor connected across terminals R and W per the T775 wiring diagram. Verify the actuator is still Series 90 compatible before completing replacement.

Application Matching Guide

Match your real-world scenario to the right T775 model. If your application spans multiple scenarios, call us.

Hot Water Reset — Boiler Supply Temp

Outdoor air sensor adjusts supply water setpoint as outside temperature drops. Standard on boiler systems for energy codes and efficiency.

→ T775R Series or T775P2003

Multi-Stage Boiler Control

4–12 staged boiler outputs with primary pump relay, equal run time sequencing, outdoor reset, and optional alarm output.

→ T775P2003 + T775S2008 (if >4 stages)

Valve or Damper Modulation

Proportional control of a hot water valve, chilled water valve, or air damper via 0–10 Vdc, 2–10 Vdc, 4–20 mA, or Series 90 signal.

→ T775M Series

Multi-Compressor Chiller Sequencing

Multiple reciprocating or scroll compressor stages with two independent setpoints, chilled water reset, and flexible stage-count distribution.

→ T775L2007 + T775S2008 (if >4 stages)

Cooling Tower or Condenser Fan Staging

On/off staging of multiple condenser fans or cooling tower fan stages from a single controller with setpoint and differential configuration.

→ T775B Series (2 or 4 relays)

Washdown or Animal Confinement Environment

Installations in poultry houses, hog confinement, swimming pool mechanical rooms, or washdown areas requiring water-resistant enclosures.

→ T775B2016, T775B2024, T775M2014, or T775M2022 (NEMA 4X)

Pressure or Humidity Control

Duct static pressure, differential pressure, or relative humidity control using a 0–10 Vdc or 4–20 mA analog sensor. Also compatible with Honeywell CO₂ sensors (output displayed in % rather than ppm).

→ T775U2006

Replacing a T991A or Other Series 1000 Controller

Have a T991A part number from the nameplate? We'll cross-reference it directly. Don't have the number — pipe size, media, voltage, and output type is enough to get you to the right T775.

→ Call (901) 458-2000

Not Sure Which T775 You Need?

Tell us your application — number of stages, whether you need reset, your sensor type, and your control signal — and we'll ID the right part number and ship it same day if it's in stock.

Request a Quote(901) 458-2000

Key Specifications — All T775 Models

These specifications apply across the T775 Series 2000 family unless otherwise noted.

SpecificationValue
Power Supply24, 120, or 240 Vac; 50/60 Hz
Power Consumption8 VA max @ 60 Hz; 10 VA max @ 50 Hz
Operating Ambient-40° to 140°F (-40° to 60°C) @ 60 Hz
Relay Rating (120 Vac)1/2 hp; 9.8 AFL, 58.8 ALR; 125 VA pilot duty
Relay Rating (240 Vac)1/2 hp; 4.9 AFL, 29.4 ALR; 125 VA pilot duty
Relay Rating (24 Vac)10A resistive
Analog Output Options0–10 Vdc (min 2,000Ω load), 2–10 Vdc, 4–20 mA (max 600Ω), Series 90, Floating
Sensor Type1,097Ω PTC @ 77°F (25°C)
Setpoint Range-40° to 248°F (-40° to 120°C)
Sensor Accuracy±1°F @ 77°F ambient (standard sensor)
Sensor Calibration±10°F / ±10% of range for non-temp sensors
Time ClockTwo settable periods per day, all models
Volatile MemoryDate/time retained 24 hours after power loss; all other settings permanent
Dimensions8-5/32" H × 4-13/32" W × 2-15/16" D
ApprovalsUL 60730-1, CuL, CE, C-tick

Frequently Asked Questions

Is the T991A really obsolete? Can I still get one?
Yes — Honeywell has discontinued the entire T991A line. New units are no longer manufactured. Some distributors may have old stock, but those are end-of-line units with no manufacturer warranty or support. The correct replacement is the T775M2006 for most T991A applications. We stock the T775M2006 and can ship same day.
What's the difference between the T775A, T775B, T775M, and T775R?
The letters define the feature set: A = basic on/off, 1 relay. B = on/off, 2–4 relays. M = modulating analog output (0–10 Vdc, 2–10 Vdc, 4–20 mA, or Series 90). R = modulating or relay with outdoor reset for hot water or chilled water applications. If you need to proportionally control a valve or damper, you need an M or R model. If you're just switching loads on and off, A or B covers it.
What sensor does the T775 use and where do I get it?
All T775 temperature inputs use a 1,097-ohm PTC sensor at 77°F. The standard sensor (50021579-001) is included with non-NEMA 4X models; NEMA 4X models include the T775-SENS-WR water-resistant sensor. Other compatible sensors include duct averaging sensors (C7031J2009, C7100D1001), immersion sensors (C7031D2003), outdoor air temperature sensors (T775-SENS-OAT), and room sensors (C7130B1009). We stock the common sensor types — call us for availability.
Can the T775 work with Series 90 actuators?
Yes. The T775M's Series 90 output mode is specifically designed for Series 90 actuators. You will need to install the included 340-ohm resistor across terminals R and W as described in the T775 installation instructions. This makes the T775M a direct functional replacement for T991A controllers that drove Series 90 actuators — the wiring terminals differ, so follow the T775 I&M sheet for the correct connection.
What's the difference between T775P and T775L for boiler/chiller applications?
The T775P is specifically designed for boilers: it has a dedicated pump output (using the last relay), three sensor inputs (supply, return, outdoor), equal run time / first-on first-off staging, and a built-in alarm output. The T775L is designed for chillers and multi-compressor systems: it sequences stages across two independent setpoints (heat and cool) with freely configurable stage distribution. For a boiler with multiple stages and a primary pump, use the T775P. For a multi-compressor chiller or reciprocating chiller, use the T775L.
Do I need a T775S expansion module?
Only if you're using a T775P or T775L base controller and need more than 4 staged relays. One T775S adds 4 relays (total 8 stages); two T775S modules add 8 relays (total 12 stages). The T775S has no independent function — it must be wired to a T775P or T775L. For any other T775 model, the T775S is not compatible.
Memphis Control Center stocks T775 controllers?
Yes — we're an authorized Honeywell distributor and stock the most common T775 configurations including T775M2006, T775B2032, T775B2040, T775P2003, and T775R2001. We ship same-day on in-stock orders placed by 2 PM CT. Call us at (901) 458-2000 with your application details and we'll confirm availability and get it out fast.

Need a T775 or a T991A Replacement?

Memphis Control Center is an authorized Honeywell distributor with T775 Series 2000 controllers in stock. Same-day shipping on in-stock orders by 2 PM CT. We'll cross-reference your T991A and get you the right T775 fast.

Request a Quote Shop Honeywell Controls Call (901) 458-2000
Authorized Honeywell Distributor Free ground shipping Ships from Memphis Same-day on in-stock orders

For emergencies, outside of business hours, call #901-604-7069