Using a Standard Thermostat with a Communicating System for Emergency Operation

On rare occasions the infinity wall controllers fail. Sometimes, this failure is after hours and the supply house is closed. Periodically, homeowners do not want to purchase another wall controller due to cost and they researched their unit on the web and read that a “regular or standard” thermostat will work their Infinity system.

I have to say first, that it is highly recommended that Infinity series equipment be used with an Infinity wall control; this way all the features of the unit the customer initially bought can be utilized and when there is a malfunction it is communicated to all the equipment to better protect against further damage. The installation manual provided from Carrier for the FE4A/FE5A does NOT show an option for wiring a standard Thermostat nor Thermidistat to the fan coil, only an Infinity wall controller. Furthermore, ALL the manuals for outdoor Infinity equipment state that an Infinity wall controller MUST be used. All manuals do say however that a standard thermostat can be used to control the unit’s control boards using emergency operation modes. There is NO guarantee that it will work indefinitely because the terminals that will be used to wire the board are intended to be outputs for a non-communicating outdoor unit not inputs from a thermostat. If the unit is being ran in emergency operation with a standard thermostat then there will be no control of humidity, no air flow staging, and the unit will not provide the level of efficiency nor comfort that they were receiving with the Infinity wall controller. Carrier states in the FE4A/FE5A manual “(Emergency mode) should only be activated when User Interface cannot be replaced immediately”.

If through troubleshooting it is found that the wall controller is faulty and must be replaced, the wall controller should be changed and replaced with a newer model. If it happens to be after hours, on the weekend, a holiday, or the wall controller is not available, then the indoor and outdoor control boards will allow emergency heating and cooling operations using a standard thermostat. If the FE4A/FE5A control board does not have communication with a wall controller for a period exceeding two minutes then the unit will flash a code 16, system communication fault.

To utilize this emergency operation modes the thermostat, fan coil, and outdoor unit must be unwired from the ABCD terminals and be rewired for R, G, W, Y, O, C. When the unit is wired appropriately, the two-minute time period has lapsed, and the indoor is flashing a code 16 on the status LED the unit will start responding to the emergency inputs. If the indoor control board retains the tonnage of the outdoor equipment, then the indoor will provide the air flow of 350 CFM times the tonnage of the outdoor. If the indoor control board DOES NOT retain the information of the outdoor equipment then the indoor board will provide 350 CFM per ton for the highest possible matched outdoor unit for each indoor unit size:

The thermostat should be programmed for either 2H/2C or 3H/2C depending on your outdoor equipment. Use the chart to wire the thermostat and follow from left to right to see where each wire will be terminated according to which model outdoor unit you have. The chart represents the latest models found in Carrier’s Catalog.