Our thermostat died yesterday, but after replacing the dead batteries with fresh batteries, and confirming the LCD screen was operable, our AC no longer turns on. I have attempted a factory reset on the thermostat, and I do hear a quiet but definitive "click" when I believe it is attempting to activate the HVAC unit, but that's as far as it gets. One theory I have is that the batteries were long dead, and the thermostat was getting it's power from the wiring directly, which means it could be the HVAC unit that died. However, it's one of the first times I've had to deal with a HVAC unit personally, so I'm guessing. I reset the breaker a couple times to see if that would do it, but it's a no go (it is clearly marked on my panel with a aluminum bridge between both breakers). Anything else I can try before I call a pro? Sounds like you may not have power from the transformer. You can check this using a multimeter, by testing the voltage between the red R wire and the blue C wire.

You should read somewhere around 24VAC, though depending on the system it could be anywhere from about 6VAC to 30VAC. Most thermostats only use the batteries to power the thermostat itself, LED display, programming, date/time, etc. Thermostats with a C wire (like yours seems to have), sometimes only use the batteries to remember your settings during a power outage. The actual power for signalling heat/cool, is supplied by a transformer in the furnace itself (the red R wire). If there is no power on the R wire, the thermostat has no way to call for heat/cool. In this case you'll have to have an HVAC tech troubleshoot, and possibly replace the transformer. You could use your multimeter to verify the furnace itself is getting power, though this is slightly more dangerous since you'll have to open the service panel on the furnace. This could put you in danger of electrocution, and should be avoided if you are not familiar with HVAC systems. The only other thing I can think for you to check, is to look for a serviceman switch and make sure it's in the ON position.

A serviceman switch is a switch on the feed line to the furnace, that allows servicemen to turn the power off to the furnace to service it. It should be located very close to the furnace, and within line of site of the furnaces service panel. If there is line of sight from the furnace service panel to the breaker panel that feed the furnace; or this is an old installation, you may not have a serviceman's switch.large ac units Your best bet, is to simply call in an HVAC technician to service the furnace.parts to outside ac unit So I had the same issue and called my buddy who is a certified HVAC technician and he helped me trouble shoot the problem. central air conditioner price compareFirst he had me check to make sure all the wires were secure behind the thermostat, but they were secure.

Then he had me take off the panel on the heater/AC Unit and push in the door trigger to see if there were lights. There were lights, which meant that power was going to the unit, just not making it to the thermostat. Then he had me check a fuse on the main circuit board that had the number 3 on it. The fuse was not blown. Next he asked me to check the AC condensation overflow pipe to make sure that there wasn't a clog because if there is a clog the safety valve will cut off power to the thermostat. Sure enough, this was the issue. There was a 1 inch PVC pipe running up along the left out-side of my AC/heater that went down into a water pump that was clogged. I simply unclogged it and the AC cut on immediately. I just had this exact issue. I called the HVAC emergency service number and the technician called me back. He advised to unscrew the bottom of the kill switch or float. There is a yellow wire that leads to it. Once I drained all the water ,the system turned on instantly. My A/C stopped working because the batteries in my (Honeywell) thermostat needed to be replaced.

I replaced them and plugged it back in the wall mount. The A/C still did not work, but the LCD lights were on. I had to remove the face plate and replug it back into the mount. This time I pressed the center of the LCD screen and got it fully connected which turned on the A/C unit. Make sure you put the batteries in right. Don't let the springs fool you like they did me. I put both batteries in with the - (minus) sides on the springs. Put one battery with the + side on the spring. It should show you the + signs on the battery holder. Before anything, try reset button at the furnace itself hidden behind the cover. It's one of those that activates when the cover is on and deactivates when the cover is off. My problem was exactly that. I put brand new Panasonic batteries in my thermostat and it did nothing. However, it worked with the old batteries, one of which was Energizer, and the other was Duracell. Clearly it takes a stronger battery.I didn't read all the responses, but thought this would help.

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. I didn't know this, as I inherited the thermostat from a friend. Heat turned on, AC did not. Once I read up, installed the jumper, everything worked fine. Hope this helps someone! Simple trick that fixed my problem. Replace the batteries but put them backwards per direction. It will shut of the lo batt warning then put the batteries correctly. Browse other questions tagged hvac thermostat or ask your own question.Using the climate control in an RV is simple, but there are a few things that make it different than using a home system. Understanding when to run the propane furnace vs. the heat pump, how to most efficiently run both A/C units and locating the remote temperature sensors will make the RV life a little more comfortable. In our first year of RV travel we must have blown through hundreds of dollars worth of propane because we didn’t understand how the heating systems worked. 

On the flip side during summer trips we ran the A/C almost non-stop because we couldn’t get the RV to cool down and stay cool.  Now we’re on our third class A RV and we like to think we’ve got it down fairly well, so I’m sharing a few of the tips and tricks we’ve learned over the years about Heating and Cooling an RV. Our Excursion is equipped with two 13,500 btu low-profile Air Conditioning Units; the bedroom A/C has a built in heat pump and living room A/C does not.  We also have two propane Furnaces for heating the RV; the furnace in the bedroom is 25,000 btu and the furnace in the living area is 20,000 btu.  All of this is controlled with the industry standard digital RV Comfort thermostat controller (at least for most class A RVs).  When I asked why we only have one A/C with a heat pump I was told the A/C units without the heat pump are a lot less expensive.  So there ya go! As with most newer RV’s the thermostat is pre-set for our specific RV climate controls. 

“Zone 1” controls the living area and “Zone 2” controls the bedroom (some RV’s have 2 separate thermostats entirely).  Our RV has two remote temperature sensors (it’s that little black plastic circle with a horizontal line through it on the wall) which is totally different than a home system where the temperature sensor is built directly into the thermostat.  The first remote sensor is located just behind the driver’s seat attached to the sidewall of a cabinet and the second is located in the bedroom near the foot of our bed.  Knowing where these little thermostats are located is important for conserving propane in the winter and electricity in the summer.  For example the thermostat in our bedroom is located just above the furnace register so in winter we have to compensate by setting the temperature higher if we want the back to stay warm.  Our sensor in the living area is located just inches from an exterior wall, the slide out and a giant window combined with the fact it’s at eye height;

so in summer the temperature here reads 5+ degrees warmer at the sensor than in the kitchen area. To rapidly cool the living area on hot days try closing all the vents in the bedroom, opening the vents on the front A/C along with all the vents in the living area, shut the door to the back area of the RV and crank up both A/C units.  Having the rear vents closed will force most of the cold air into the larger part of the coach and help it cool down quickly.  If necessary close all the shades, especially if the sun is coming in the driver’s area.  Of course you may need to do the “power shuffle” if you’re connected to 30a shore power! When driving an RV in the Summer the heat can be a beast!  The built in HVAC for the cab is nowhere near strong enough to cool the entire RV, so when you’re driving in extreme heat it may be necessary to run the generator to power the living area A/C to cool down the RV.  I’ve even had RVers tell me that running the generator to power the roof A/C is more fuel efficient than running the cab A/C, although I haven’t done any extensive testing of this theory myself. 

We have driven through the desert a few times in the summer and I know it sounds ridiculous but sometimes you really need to run both A/C units to survive the heat coming in through the giant windshield, this was especially an issue with our first 2 Front Engine Diesel RVs.  While driving the Excursion in warmer months we try and keep the bedroom door closed, and all the rear A/C vents closed, because the rear engine diesel leaks a lot of heat into the back of the RV.  If we were in a gas coach that heat would be up front by our feet, so this is where a rear engine diesel comes in handy.  However in the winter it’s the opposite. (see our post on diesel vs gas here) A few things I have learned (the hard way): 1. Our first class A RV was 31 feet and only had one 15,000 btu A/C unit.  I remember sitting at the lake in Dallas, with the temperatures soaring into the triple digits…that A/C ran non-stop and the temperature inside the RV never cooled below 94 degrees.  One A/C unit is not enough to cool a 28’ or larger RV in high temps, you need two A/C’s!

2. If you want to capture the condensation water from the A/C unit it is possible to distill the water or at least kill the bacteria with a Camelbak All-Clear type of device.  I am mentioning this because I keep getting asked and I’m not sure why, my opinion is if you’re running the A/C enough to produce that much water then you’re not really worried about conserving energy so why bother capturing a few ounces of water? 3.  A Tree is your friend!  If you can find a spot by even one small tree you can drastically reduce the heat inside your RV.  Try to find a tree to block the windshield or the driver’s side of the RV, and put out your awning to cast as much shade around the RV as possible. 4.  If you’re trying to Wild Camp in hot temperatures then you’re in for a real battle!  Trees are good for temperatures but bad for solar, this is where a portable solar kit may come in handy.  You could also create an evaporative swamp cooler and install a couple of (amazon link so you can see what I am talking about) MaxxFan With Remote Control powered vents that have the “auto” temperature setting so they open and close as the temperature changes inside the RV.

5. Do not run the dash A/C when climbing giant hills, or mountains, in the desert…you can overheat the engine!  If it’s “Hotter than Hades” and you see a mountain in the distance, turn off the cab A/C, crank on the generator and run the roof A/C…or you can always turn it all off and suffer through. Furnace – We rarely use the furnace because it burns through propane like it’s going out of style.  The two instances where we most use the furnace: 1. During Wild Camping in cold temps we sometimes kick it on for a few minutes to warm up the coach in the morning, but mainly we use it to warm up the bathroom area just before taking a shower, ’cause nothings worse than stepping out of a ‘navy’ shower into a 40 degree bathroom.  2. If the temperatures are near or below freezing we’ll set the furnace temperature to 50 degrees so the RV doesn’t freeze.  If you plan on RVing in freezing temps make sure you have a full tank of propane and watch our videos on How to Prepare an RV for Winter Camping.

Heat Pump – The heat pump is built into the AC and works great if you use it correctly.  From my experience and mistakes I’ve learned a lot about this little heat pump: 1. The Heat Pump does not work when temperatures are below 45 degrees. 2. Do not attempt to run the heat pump when plugged into a 20a outlet, use the heat pump when you’re plugged into a 30a or 50a plug. 3.  Cranking the thermostat way up when using the heat pump will cause the propane furnace to kick in, now you’re wasting propane and using electricity which is pointless (unless your goal is to heat up the RV as quickly as possible).  Many thermostats are setup so both the furnace and the heat pump kick on when you select a temperature that is more than 5 degrees higher than the current temperature.  When heating the RV with the heat pump I increase the temperature setting in 4 degree increments, which keeps the propane furnace from ever kicking on. I haven’t found any RV Climate Control system that I think is perfect, however with a little tweaking, a little extra knowledge, and some insights from your favorite mistake maker (that’s me), keeping the RV comfortable is a breeze (haha, funny right?).