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Troubleshooting Thermostats - Legacy RC series

Thermostat resets when calling for heat or cool:

 

1.       How many HVAC wires are installed on the thermostat? 

 

In a heat only or cool only application, a minimum of three wires is required.  A common wire is always required in a heat only or cool only application.

 

2.       If it is a heating and cooling application, is the common wire installed?

 

The RC-80 Thermostat was designed to work with most 4 wire HVAC systems.  The transformer common (C) is usually not required, because the RC-80 can power steal (to maintain operating power when the heating or cooling relay is engaged) from the W (heat relay), Y (cool relay), and G (fan relay).  If the heat, cool, or fan relay cannot supply 15mA to power thermostat without the relay activating, a common wire or the following procedure in this application is required.

 

Whenever feasible (if an additional wire is present or can easily be installed), it is recommended that a connection be made between the transformer common and the (C) terminal on the RC-80 Thermostat.  In new construction installations, inform the HVAC contractor to run a minimum of 5 wires between the thermostat and the HVAC system, with one connected to the transformer common.

 

Note:  The RC-80 requires an additional 3-conductor wire from the thermostat to the automation controller for communications.

 

In a scenario where the RC-80 thermostat resets when calling for heat or cool (and no common wire is present or can easily be installed), refer to procedure TN: 1 and TN: 2.

 

3.       Is the thermostat losing power when calling for heat or cool (is the HVAC transformer dropping power)?

 

All HAI RC-Series communicating thermostats require 20 to 30 volts AC to operate.  This power must be on continuously.  Any momentary dip or cut out of power will be seen as a power failure and cause the thermostat to reset and wait the minimum off time to restart.

 

Version 1.5 and earlier thermostats are AC only.  They must be powered by an AC circuit, which is standard for HVAC systems.  Versions 1.6 and later can operate from AC or DC power supplies, 20 to 30 volts.

 

If power problems are suspected, use a good voltmeter set to AC VOLTS and measure between the R wire and any of the other wires (C, W, Y, or G).  You should read between 20 and 30 volts AC.  Higher or lower voltages will cause problems.

 

Another test would be to connect a 24-volt light bulb between R and C on the thermostat, or at the HVAC system if transformer common (C) is not wired to the thermostat.  Route the wires through the air vents on the thermostat mounting plate, and install the thermostat.  If this light blinks or goes off during a call for heating or cooling, the furnace is cutting power to the thermostat and causing it to reset.  Refer to TI: 1 for illustration.

 

Most HVAC systems are designed to provide continuous power to the thermostat, since many modern thermostats require continuous power.  Cut outs, sags, etc. in the 24-volt thermostat circuits are not normal.  Check the furnace door switch, wiring connections, transformer, and HVAC controller for possible trouble.

 

Thermostat is not heating or cooling:

 

1.       What is the current temperature?  What is the current mode?  What is the desired temperature setting (press the up or down arrow key once to view the desired setting)?

 

If the current mode is off, the thermostat will not call for heat or cool.

 

In heat mode, if the desired temperature is above the current temperature the thermostat will not call for heat.

 

In cool mode, if the desired temperature is below the current temperature, the thermostat will not call for cool.

 

2.       If the thermostat should be calling for heat or cool (based on current and desired temperature settings), is the star («) lit on the thermostat display?

 

If the star is lit on the thermostat display and the heating or cooling system isn't turned on, refer to TN3.

 

3.       If the star isn't lit on the thermostat display, press the Prog key 3 times, and then press the Fan key 2 times.  Did the star appear on the display?

 

If the star appeared on the display, verify that the heating and cooling system is turned on.  If not refer to TN3.

 

If all of the segments light up (all characters that can be displayed are showing at once), this would indicate that the thermostat reset when calling for heat or cool.  Refer to topic "Thermostat resets when calling for heat or cool".

 

Note:  There are delays (the compressor start up delay and minimum on/off times) which prevent the thermostat from starting the heating and cooling equipment.  For testing purposes, these delays can be canceled.  To cancel a delay, press the Prog key 3 times, and then press the Fan key 2 times.

 

Temperature is not displayed on system console:

 

1.       How many thermostats are installed?  Does each thermostat have its own address?

 

If more than 1 thermostat is installed, each thermostat must be set to a different address.  If connected to an Omni system, each thermostat must be set to a consecutive address, starting at 1.  If connected to an OmniPro or Aegis, each thermostat must be set to a different address, but it is not necessary to address each thermostat consecutively.

 

To view the current address of a thermostat, press the Prog key three times (day will flash), then press the fan key.  The small digit on the top of the display is the item number (00-Address).  The large blinking digit in the center of the display is the value (address) of the item number.

 

2.       Is the communication mode properly set to System mode?

 

The thermostat can communicate in several different modes.  When connected to an automation system (Omni, OmniPro, Aegis. etc.), the communication mode must be set to 1 (System mode, 100 baud).

 

To view the current communication mode of a thermostat, press the Prog key three times (day will flash), press the fan key, then press the Prog once more.  The small digit on the top of the display is the item number (01-Communication mode).  The large blinking digit in the center of the display is the value (communication mode) of the item number.

 

3.       Is the automation system properly configured for thermostats?

 

On an Omni system, under Setup | Installer | Temperature, you must specify the number of thermostats that are connected (each must have a consecutive address).  Up to four thermostats can be connected to an Omni system.

 

On an OmniPro and Aegis system, under Setup | Installer | Temperature, you must specify the thermostat type for each thermostat.  When thermostats are used, they must be configured to the applicable thermostat type.

 

To view the status (temperature and other settings) of a thermostat at a console, from the top-level display or from the main menu, press the 5 (TEMP) key on the console keypad.

 

You will be prompted with the first named temperature zone (i.e. Upstairs).  The temperature zone can be specified by entering the temperature zone number followed by the ' # ' key, or by pressing the arrow keys to scroll through the list of temperature zones.  Press the ' # ' key when the desired temperature zone is shown. 

 

                  TEMPERATURE ZONE:

                  ENTER TEMPERATURE ZONE ¯

 

After the ' # ' key is pressed, a menu appropriate for the type of temperature zone is shown.  Press  ' # ' to view status. 

 

                  Upstairs      TEMP: 78

                  HEAT: 70      COOL: 78  ¯

 

4.       Is the temperature display correct?

 

5.       If not, can you send a command to the thermostat?

 

To send a command to the thermostat from the status display on the console, press the ' * ' key.  A menu presenting options appropriate for that type of thermostat is displayed.

 

                  Upstairs

                  1=MODE  2=HEAT  3=COOL ¯

 

Press the 1 (MODE) key to change system mode on a thermostat. 

 

                                                Upstairs MODE          

                  0=OFF   1=HEAT  2=COOL ¯

           

                  Upstairs MODE

                  3=AUTO                 ­

 

From the console, change the thermostat mode.  If the thermostat is currently displaying "AUTO" mode, change the mode to "OFF" mode.

 

6.       Did the thermostat change mode?

 

After the command is sent from the system, the thermostat mode should change to the selected mode.  Also, "REMOTE" should be displayed on the thermostat, signifying the thermostat received a command from the remote system.

 

If the thermostat did receive the remote command and is now properly displaying the proper mode and the "REMOTE" icon, check for proper thermostat communication wiring.

 

Remove the thermostat face from the base.  Observe the thermostat communication cable.  The black and red conductor on the communication cable should be spliced together.  The black and red conductor must be grounded back at the controller.  This is a common problem with thermostat installations.  If the red conductor isn't properly grounded, the thermostat can receive commands from the system, however it can not send the proper information back to the system. 

 

7.       If the thermostat did not receive the command, check the output by connecting a 12-volt light bulb between Output 8 and Ground.  Is the light flickering on and off?  If a 12-volt light bulb is not available, use a DC voltmeter.  Can you see a transition between 0 and 12 volts?

 

If the bulb doesn't flicker or the meter doesn't show a transition, the chip U31 (UND2981) that drives the outputs is suspect.  Replace U31 and confirm that the temperature is properly displayed.

 

Note:      U31 drives all 8 outputs.  A maximum of 100 mA can be drawn from each output.  If anything connected to any output draws more than 100 mA, the chip can be destroyed causing all outputs not to function.

 

The air conditioner starts before the desired setting:

 

1.       In cool mode, why does the air conditioner start before the temperature reaches the desired setting?

 

Check the cooling anticipator.  This item adjusts the tendency of the thermostat to run the cooling system to refresh and dehumidify the air before the temperature rises to the desired cool setting.  A setting of 0 will disable this feature.

 

0                      No anticipation

 

3-5                   Normal anticipation

 

10                    Maximum anticipation

 

The recommended setting for most forced air cooling systems is 4.  A lower number will decrease the tendency to run the cooling system below the cooling setting.  A lower setting of 2 or 3 may be desired in dry climates. 

 

The default setting is 4.

 

      Note:        HAI thermostats automatically set the maximum cycles per hour by using a "Cooling minimum on/off time".  This is used to limit the on and off times of the cooling system.  When the cooling system starts, it must remain on for the minimum time set by this item.  When the cooling system turns off, it must remain off for a minimum time set by this item.  This item takes priority over the cooling anticipator.

 

Temperature settings change involuntarily:

 

1.       Is the thermostat's internal "clock-programming" enabled?

 

The RC-Series Thermostats are pre-programmed at the factory with energy saving settings in order to gain certification under the EPA Energy Star program.  When used with a HAI automation system, the thermostat should be set as  "non-programmable" (See Setup Item 03 - "Display Options").

 

      03     Display options

 

      The thermostat can be configured to display the following attributes:

 

       0       Celsius                   am/pm time format                programmable

 

       1       Fahrenheit             am/pm time format                programmable

 

       2       Celsius                   24-hour time format              programmable

 

       3       Fahrenheit             24-hour time format              programmable

 

       4       Celsius                   am/pm time format                non-programmable              

 

       5       Fahrenheit             am/pm time format                non-programmable

 

       6       Celsius                   24-hour time format              non-programmable

 

       7       Fahrenheit             24-hour time format              non-programmable

 

When connected to the HAI system, the internal "clock-programs" will interfere with the automatic event scheduling (automation programs) of the HAI system.  All programming schedules of the thermostat can be duplicated by HAI system but with much more flexibility and a greater level of sophistication.  You are not limited to the number of programming changes that can be scheduled beyond the total program capacity of the HAI system.


 

 

We strongly recommended that you disable the internal "clock-programming" when connected to a HAI system.

 

2.       Are heat and cool settings overlapping?

 

The heat setting is always lower than the cool setting.  There is a minimum 3-degree difference between the heat and cool setting.  If the cool setting is set lower than the current heat setting, the heat setting will automatically be lowered to maintain the 3-degree difference.  If the heat setting is set higher than the current cool setting, the cool setting will automatically be raised to maintain the 3-degree difference.

 

Check the programs that affect the heat and cool settings.  Make sure that the desired heat and cool settings maintain a 3-degree difference.  For example:

 

7:00 AM MTWTFSS: TSTAT1 HEAT 75

7:00 AM MTWTFSS: TSTAT1 COOL 76

 

At 7:00 AM, the heat setting will be set to 75.  Immediately after that program, the cool setting will be set to 76.  When this happens, the heat setting will automatically be bumped down to 73 to maintain the 3-degree difference.  This may give the appearance of the heat setting involuntarily changing.

 

Outdoor temperature is not displayed on the thermostat:

 

1.       Is an HAI Outdoor Temperature Sensor connected to the controller?

 

To send the outdoor temperature to the RC-Series Thermostat, an HAI Outdoor Temperature Sensor must be connected to a zone input on the HAI controller.  Check for proper connection and that the zone is properly configured an Outdoor Temperature Zone (Type 81).

 

2.       Is the Outdoor Temperature displayed on the system console?

 

If the Outdoor Temperature Sensor is properly connected, properly configured, and is properly functioning, the temperature can be display at the system console.  To display the temperature of an Outdoor Temperature Sensor at a console, press the 5 (TEMP) key on the console keypad.

 

You will be prompted with the first named temperature zone (i.e. Upstairs).  The temperature zone can be specified by entering the temperature zone number followed by the ' # ' key, or by pressing the arrow keys to scroll through the list of temperature zones.  Press the ' # ' key when the desired temperature zone is shown. 

 

            TEMPERATURE ZONE:

            ENTER TEMPERATURE ZONE ¯

 

After the ' # ' key is pressed, a menu appropriate for the type of temperature zone is shown.  Press the ' # ' key to view status. 

 

            OUTDOOR TEMP  TEMP: 78

                  LOW : 40      HIGH: 95  ¯

 

If the temperature isn't displayed, check the wiring and zone definition.  Try connecting the sensor to another zone (don't forget to configure the new zone to Type 81).  If the console still doesn't display the temperature, the Outdoor Temperature Sensor is defective.  Return the Outdoor Temperature Sensor for repair.

 

3.       If the outdoor temperature is displayed at the console, can you send commands to the thermostat?

 

From the console, use the temperature menu to send a command to the thermostat.  For instance, if the current mode of the thermostat is Cool, use the console to change the mode to Off.


 

 

4.       If the thermostat responds to commands from the console, are any other zones configured as an "Outdoor Temperature Sensor"?

 

If any other zone (a zone preceding the zone where the temperature sensor is actually connected) is configured as Outdoor Temperature, the controller will attempt to send the temperature from the first configured zone.  If nothing is connected to zone configured as an Outdoor Temperature, the outdoor temperature will not be sent to the thermostat.

 

At the console, check each zone type.  If any zone (other than the zone where the temperature sensor is connected) is configured as an Outdoor Temperature, change the zone type.

 

 

 

 


 

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