Your furnace or central air conditioner spends a good amount of energy simply turning on and off, which is why you want yours to run for at least 15 minutes at a time before shutting off. Your air conditioner’s job is to carry hot air out of the home and blow cool air in. I have a programmable thermostat at home. Large holes or openings behind thermostats could also cause inaccurate temperature readings. For most cars the air conditioning is powered by a belt from the engine and even if the car is only idling it will be running without any meaningful effect on the car's battery. Check thermostat location: The location of your thermostat can affect how it functions. Low battery indicator light on your thermostat that may also include a beep from your thermostat unit. How to change the batteries in your thermostat will depend on its make and model, but most thermostats have a removable battery compartment that is easily accessible. If your thermostat has a R and Rc, then there has to be a physical wire (jumper) connecting the R and Rc, along with the red wire going into the R slot. You get a blank screen and can’t set your thermostat or turn your HVAC system on. The simplest answer is also the most likely: The thermostat is old or just faulty. A weak car battery can cause your auto air conditioner to function poorly or not at all. Here’s how you change the batteries. Car batteries need to have enough voltage to trigger the AC compressor, and while it may be strong enough to run the rest of your car, it may still be too weak to run your car's air conditioning. There are a number of problems that the AC thermostat can cause, including refusing to allow the air conditioner to turn on at all and not letting it reach the programmed setting. The fan on the unit kept blowing, but only moving warm air. The temperature settings you program into a digital wall thermostat don’t impact battery usage (e.g., turning down the air conditioning in the summer won’t save the battery life of your thermostat; you’ll just save on your energy bills). I noticed the "replace batteries" indicator came on the other day on my way out the door to work. Your air conditioning or furnace isn’t operating quite reliably. Pry out the old batteries by setting a small, flat-blade screwdriver into the slots and lifting up. Depending on the brand, here are two recommendations: If your thermostat has an external battery compartment. Heat turned on, AC did not. I didn't read all the responses, but thought this would help. How can you change the batteries? Issues That Can Affect Air Conditioning in a Home. Last night my AC condenser stopped working. Can low thermostat batteries cause an AC condensor to stop? Can a low battery affect air conditioning? Turn the wall thermostat housing over to find the battery removal slots. Look straight on at your thermostat; you will see a place where you can press down to release the compartment on the top right side of the thermostat. The batteries in your thermostat can last as long as five years or as little as a few months – so if your thermostat is turned on but still blank, try swapping out the batteries. Thermostat Troubles Can Cause Short Cycling. Your thermostat could also cause the HVAC system to cycle on and off rapidly, a process known as short cycling. I didn't know this, as I inherited the thermostat from a friend. An AC thermostat that won't work can be incredibly annoying. A thermostat in direct sunlight, for example, will sense warmer temperatures and will respond as if the indoor temperature is hotter than it actually is. OK. Light on your thermostat could also cause inaccurate temperature readings thermostat that n't. 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