Pro1 T621-2 Non-Programable Thermostats Installation Manual


Pro1 T621-2 Non-Programable Thermostats 


Thermostat Application Guide

Gas or Oil Heat Yes
Electric Furnace Yes
Heat Pump (No Aux. or Emergency Heat) Yes
Heat Pump (With Aux. or Emergency Heat) Yes
Multi-Stage Systems Yes
Heat Only Systems Yes
Heat Only Systems – Floor or Wall Furnace Yes
Cool Only Systems Yes
Millivolt Yes


  • The display range of temperature … 41˚F to 95˚F (5˚C to 35˚C)
  • The control range of temperature…. 44˚F to 90˚F (7˚C to 32˚C)
  • Swing (cycle rate or differential) …… The heating is adjustable from 0.2˚ to 2.0˚
    Cooling is adjustable from 0.2˚ to 2.0˚
  • Power source …………………………………….18 to 30 VAC, NEC Class II, 50/60 Hz for hardwire Battery power from 2 AA Alkaline batteries
  • Operating ambient …………………………. 32˚F to +105˚F (0˚C to +41˚C)
  • Operating humidity ………………………… 90% non-condensing maximum
  • Dimensions of thermostat …………….. 4.7”W x 4.4”H x 1.1”D

Power Type

  • Battery Power
  • Hardwire (Common Wire)
  • Hardwire (Common Wire) with
  • Battery Backup

A trained, experienced technician must install this product.
Carefully read these instructions. You could damage this product or cause a hazardous condition if you fail to follow these instructions.

Wall Locations

The thermostat should be installed approximately 4 to 5 feet above the floor. Select an area with average temperature and good air circulation.


Do not install thermostats in locations:

  • Close to hot or cold air ducts
  • That are in direct sunlight
  • With an outside wall behind the thermostat
  • In areas that do not require conditioning
  • Where there are dead spots or drafts (in corners or behind doors)
  • Where there might be concealed chimneys or pipes

Installation Tip

Pick an installation location that is easy for the user to access. The temperature of the location should be representative of the building.

Subbase Installation

  1. Horizontal Mount
  2. Vertical Mount


For vertical mount put one screw on the top and one screw on the bottom.
For horizontal mount put one screw on the left and one screw on the right.

Installation Tip: Electrical Hazard

Failure to disconnect the power before beginning to install this product can cause electrical shock or equipment damage.

Mercury Notice

All of our products are mercury-free. However, if the product you are replacing contains mercury, dispose of it properly. Your local waste management authority can give you instructions on recycling and proper disposal or you can mail the thermostat to the address on the warranty section for proper disposal.

Installation Tips

Mount Thermostat

Align the 4 tabs on the subbase with corresponding slots on the back of the thermostat, then push gently until the thermostat snaps in place.
Battery Installation
Battery installation is recommended even if the thermostat is hardwired (C terminal connected). When the thermostat is hardwired and batteries are installed, the thermostat will activate a compressor delay of 5 minutes when the thermostat detects a power outage from the hardwired power supply.

High-quality alkaline batteries are recommended. Rechargeable batteries or low-quality batteries do not guarantee a 1-year life span.


Conventional & Heat Pump


The switch converts the thermostats between conventional and heat pump operation.
Heat Pump: Configures the thermostat for heat pump operations.
Conventional: Configures the thermostat for conventional operations.

Conventional/Heat Pump Switch

Thermostat Quick Reference

Getting to know your thermostat


  1. LCD
  2. Temperature setpoint buttons
  3. Fan switch
  4. Easy change battery door

Removing The Private Label Badge


Gently slide a screwdriver into the bottom edge of the badge. Gently turn the screwdriver counterclockwise. The badge is held on by a magnet in the well of the battery door. The badge should pry off easily. DO NOT USE FORCE.

About The Badge

All of our thermostats use the same universal magnetic badge. Visit the company website to learn more about our free private label program.

NOTE: The compressor delay feature is active if ON is flashing. The compressor will not turn on until the 5 minute delay has elapsed.


The low battery icon is displayed when the AA battery power is low. Whenever the thermostat detects low battery voltage from the AA batteries, the low battery icon will begin flashing on the screen for 21 days (if the batteries are not changed). If the batteries are not changed 22 days after the thermostat detects low battery voltage, the thermostat screen will only show the flashing battery icon until buttons are pressed. If the batteries are not changed 43 days after the thermostat detects low battery voltage, the thermostat screen will only show the flashing battery icon until buttons are pressed and the set points will offset to 85°F/29°C in cooling and 55°F/13°C in heating. At this stage, set point changes can be made temporarily but, the set points will change back to defaulted values after a 4-hour period. The thermostat will continue to perform this low battery flashing, temperature offset condition until the internal voltage threshold is reached. When the thermostat’s internal voltage threshold is reached, all relays will be opened and the thermostat will become inoperable until new batteries are installed.


Electrical Hazard

Failure to disconnect the power before beginning to install this product can cause electrical shock or equipment damage.


All components of the control system and the thermostat installation must conform to Class II circuits per the NEC Code.

  1. If you are replacing a thermostat, make note of the terminal connections on the thermostat that is being replaced. In some cases, the wiring connections will not be color coded. For example, the green wire may not be connected to the G terminal.
  2. Loosen the terminal block screws. Insert wires then retighten terminal block screws.
  3. Place nonflammable insulation into the wall opening to prevent drafts.

Installation Tip

Do not overtighten terminal block screws, as this can damage the terminal block. A damaged terminal block can keep the thermostat from fitting on the sub-base correctly or cause system operation issues.
Max Torque = 6in-lbs.

Terminal Designations

Heat Pump System 1 HEAT 1 COOL / 2 HEAT 1 COOL           Conventional System 1 HEAT 1 COOL / 2 HEAT 1 COOL

R Transformer Power Transformer Power
C Transformer Common Transformer Common
B Changeover Valve Energized in HEAT Energized in HEAT
O Changeover Valve Energized in COOL Energized in COOL
G Fan Relay Fan Relay
W/E First Stage of Emergency HEAT First Stage of HEAT
W2 Second Stage of HEAT/ EMERGENCY HEAT Second Stage of HEAT
Y First Stage of HEAT and COOL First Stage of COOL
  1. Power supply
  2. Use either O or B terminals for the changeover valve.
  3. Optional 24 VAC common connection when the thermostat is used in battery power mode.
  4. Factory-supplied jumper


Technician Setup

Tech Settings

  1. Select OFF with the System Switch.
  2. Press and hold the + and – buttons together for 3 seconds.
  3. Use the + and – to change setting for that step, press the + and – simultaneously to change between tech settings.
    To exit Tech Settings, slide the System Switch to a different position or wait approximately 20 seconds.

Pro1-T621-2-Non-Programable-Thermostats-FIG.10 Pro1-T621-2-Non-Programable-Thermostats-FIG.11


Download Manual:

Pro1 T621-2 Non-Programable Thermosts Installation Manual

other manuals:

Pro1 T621-2 Non-Programable Thermosts Operation Manual


Pro1 T621-2 Non-Programable Thermostats Installation Manual


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