Tip & How-To about Heating & Cooling

Buying the right Thermostat for your Heating/Cooling system

When you feel the need to change you're room thermostat, keep in mind the one that you are changing out, and the type of system you are controlling, such as a Heat Pump split system, or package Heat Pump, a gas fired furnace with a central air conditioning which can also be split or a package unit on the roof or ground, heat or cooling only. For a Heat Pump, you will need a H.P. T-stat as there are up to 8 control wires for these units, to control emergency heat, aux. heat, reversing valve ect. Gas/Electric require only 4 wires, but normally a contractor will pull 5 conductors, one for a spare. On gas/elect. units, the terminals you will see on the new Thermostat will be RH, RC.1st of all, this stands for Red heating, and Red cooling. There will be a jumper wire connecting the 2. The reason for this, is the system you have most always will have only one transformer, to control both heat and cool. If you had a 2 transformer system, you would not need the jumper and you would have 2 hot wires, one for heat and one for cool. They only make these 2 transformer systems for commercial units now, so no worries. Next you will have a white wire.This is for you're heater. There will be a W terminal to connect to. Next, a Green wire, this is for the fan operation, a G terminal. Last you will have a Yellow wire which is for the cooling. Marked Y on the thermostat. In rare cases, they will use the blue wire for cooling. If this is the case, hook the blue to the Y terminal. Now you are ready to program the time and temperature's. Now, if you find you have only 2 wires to work with, red and white, you would more then likely have a heater only. No worries, just terminate the red to RH and white to W. If you happen to have a third wire such as green or blue, this will go to the G terminal for the fan. This goes for a cooling only unit.Red to RC, and white to Y. When using only heat or cooling alone, remove the jumper wire only under this condition. Remember, RH is for heat only, and RC for cool only. You're red 24volt hot wire will terminate there. Now, on a Heat- Pump system, pull off the face plate 1st. The thermostat connects to the sub-base behind it with several small screws. Remove it to expose all wiring and terminals. Due to the fact that most all heat pumps terminate differently, it is VERY IMPORTANT to mark each wire to the correct terminals as 0 to 0, or 0 to B, Y to W-1 ect. Make you make a drawing that you can understand, and mark each wire to what terminal it connects to. Heat-Pumps have several different terminations you must follow, and if possible, buy the stat before you remove the sub-base. Just take the name and any part numbers you may find with you, also you're diagram noting terminals. This way you will no for sure it will be correct. Please don't let this scare or confuse you, I just want to point out that Heat-Pumps have many terminations and you must follow instructions. This should have been noted 1st, but even though us contractors in this field change a thermostat without turning off the power, be sure you turn it off. If not, you may get a light tingle, but you can short out the new stat.Please make a copy of this to keep on hand, and I sincerely hope this has given you some insight on wiring up thermostats.Also, keep the manual that comes with the stat for programming and instructions for different terminations. Best of Luck to all and Sincerely,
Shastalaker7

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2 Answers

Where is the thermostat on 2000 Mercury Sable ?


Anmar. It won't be the thermostat...Sable and Taurus have a design problem. The heater core hose going into heater core from water pump gets plugged up right at the heater core bypass junction. At Hardware store..Buy hard plastic hose/tubing about 4ft long that just fits inside of the heater core hose. My ACE hardware has white hard tubing. Cut one end of the hard tubing at angle to use it as a reamer inside the heater core hose. Now place the hard tubing on top of heater hose to measure the distance on hard tubing it has to travel up to firewall . Mark with black marker on hard tubing. Remove the heater core hose from top of water pump and slide hard tubing in hose all the way up to where the bypass connection is feeling the obstruction...rotating the hard tubing as you gently shove it thru heater core hose. Slide it back and forth and keep rotating it until you feel it go past the Bypass junction...10 min at least. Now take off the heater hose from engine on driver side that comes from the heater exit side...Use garden hose high pressure and back flush the crud out. Re connect hoses, add fluid to reservoir as needed. Or take to shop and have them do this. Many shops just back flush...Have them do BOTH! Buy the plastic tubing ahead of time so they have no excuse. I have been doing this on my 98 Taurus since 1999. Done many of these...If you haven't changed thermostat for 4 years ...Change that as well. You tube has videos. Email me at davefudally@hotmail.com I promise you hot air...from the car!

Jan 01, 2015 | 2000 Mercury Sable

1 Answer

thermostat location on York Diamond 90 gas furnace


Augold, sometimes its best to set the thermostat where you "feel comfortable" . I.E. set it and leave it til you feel the need to be cooler or warmer.

A thermometer on a thermostat will not always be accurate and setting it will only get it within 2 to 5 degrees which is enough to "feel".

Now from the stand point of is it working properly????

Assume you feel comfortable and the heat stays on to keep you comfortable is their anything wrong with this? I assume this is the goal. Even if it says 90 (and you know its not 90) and your comfortable you could leave it alone and be OK. If this kind of thing is whats bothering you a new thermostat may not be much better, unless your ready to invest in one and accept it however it should be closer to the place youd set it. Id recommend an electronic type they are more accurate and level doesn't matter so much to these types.

If you want to set the temperature and are determined to go by a thermometer to "feel Comfortable" I recommend you buy an electronic thermometer and set it close by the thermostat. Make sure you have no lamps or other heat sources close to the thermostat area.
Remember the far end of a room or a chair by a window Especially with little or no curtains and on the prevailing out door wind will always feel colder and be colder than the area by the thermostat even if both are in the same room. If your too cold try running the thermostat up a few degrees. If too warm set it lower. The equipment doesn't care how cold or warm it is.You will not increase your utility bills to the national debt by being comfortable

If this helps please grade me accordingly and Good Luck.

Mar 03, 2009 | Weather King 10AJA3601AH Air Conditioner

1 Answer

central haeting keeps turning on when itself


Change your air filter, if the system has to work too hard, it will over heat. If the filter is allowing air flow and the system still shuts off it is the thermostat. Keep in mind the Thermostat gauges the temperature where the thermostat is located, if its next to a running fireplace it will think your entire house is that temp.

Feb 02, 2009 | Water Heaters

2 Answers

with new digital thermostat furnace runs every 10 min.


which type of T-Stat is it ? most standard t-stats have it built in that the temperature range is only a half a degree, it may seem like its running alot more, but in actuality it is maintaining better home comfort as it is not running as long as the old bimetal t-stats which would have a range of anywhere from 2-5 degrees which would cause the furnace to run alot longer, use more energy, use more fuel, and you would notice a definate change in the house temperture before it would come on or shut off, your t-stat seems to be working properly, and it will save you money, remeber also to change those filters !!!

Jan 20, 2009 | Honeywell Programmable Thermostat Heater

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