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Thermostat Problems

What is a thermostat and what are the most common thermostat issues?

A thermostat is a temperature control device that is part of most HVAC equipment like air conditioners and furnaces. Once it is set to a specific temperature, it regulates the operation of the equipment to allow that temperature to be maintained. The most common thermostat issues include units that are not working, those that do not maintain the required temperature, problems thermostat connections and display messages that are not clear. Many times when facing these types of thermostat issues, an Expert may be needed. Read below where Experts have given answers to various thermostat questions.

I accidently pulled out the thermostat wire on the outdoor unit of my carrier air conditioner. I reconnected it but the AC is not working. What Should I do?

If you are sure that the thermostat wiring has been reconnected correctly, the likely cause of your problem is a blown low voltage fuse caused by a short circuit when the wire was pulled out. To check this, switch on the fan at the thermostat. If the blower does not start, go to the indoor unit and look inside to find a circuit board. There should be a small fuse, like you have in cars, fitted there. Pull out the fuse and if it has blown, replace it with a fuse of the same rating which is usually 3 amps. The unit should now work properly.

The thermostat on my Lennox model MN HPXA16-048-230-01 shows the unit is cooling but only warm air comes from it. All the breakers and fuses are intact and I have changed the battery in the unit. Is this a thermostat problem? How Do I check it?

It is likely to be a thermostat issue. To check please take the cover off the thermostat to expose the wire connections behind it on the wall mount. Locate the Y and R connections. Straighten out a paper clip and jump the 2 terminals. If the unit comes on and blows cold air, the thermostat is most likely defective.

The thermostat on my Honeywell air conditioner model TH4110D displays a “Recovery” message. What does this mean? Is there a problem that requires thermostat troubleshooting?

The Recovery message does not indicate a thermostat problem. This model air conditioner has a thermostat with ‘adaptive intelligent recovery.’ Suppose you have set the thermostat to start at 6PM and maintain 72 degrees. Over the last few days the thermostat has learned that it takes about 1 hour for the unit to bring the temperature down by 5 degrees. At 5PM the temperature is 77 degrees so the unit comes on at 5PM so that the desired temperature is achieved by 6PM. While in this mode the display will read Recovery which does not indicate a problem with your air conditioner. However, if the unit is not working when the thermostat indicates Recovery, there may be a problem with your unit which needs to be checked.

I have a thermostat wiring question. I am replacing my Honeywell thermostat with a Nest unit. The old unit has wires labeled 1, 2, 3 and 4 but the new one has color coding like rh, w and so on. How can I match the numbers to the colors?

There is no universal code that enables numbered and color coded wiring to be matched. Making a mistake with the wiring could result in blown fuses, damaged control boards and thermostats and other problems. One thing you could try is checking furnace / air hander to see if the colors of the wires on the board match the colors on the new thermostat. If so, turn off the power to the system and connect the new thermostat as the colors indicate. Please note that wiring can change from system to system and there are no fixed rules or conventions that are followed in regard to color coding or numbering the wires. In most case, matching the board and the thermostat wires for wire should solve your problem. If you have doubts or are uncertain on how to proceed it may be better to call a qualified technician to replace the thermostat.

I want to reprogram my White Rodgers thermostat from scratch. I have followed the procedure given in the instruction manual but it doesn't to hold the time or temperature settings. Please let me know the right way to program the thermostat.

The correct procedure for reprogramming the thermostat is to first turn off power to the unit and then remove the batteries and wait for a few minutes. Now replace the batteries and turn on the power. The thermostat should now revert to the default settings. To change this press the ‘Program’ or ‘Set” button. A time and temperature should appear on the display. Use the arrow to set the temperature you want. Press the button again and a new time and temperature will appear. Change the temperature as before. Repeat this process until the thermostat has been programmed the way you want. If your settings are not retained or it keeps reverting to the default settings then it is likely that the thermostat is damaged and will need to be replaced.
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    I have a nest thermostat and I installed it. But I'm not sure if the blue wire should go to Y2 or to the G terminal.
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