However, if your system is unique, finding a replacement thermostat may be difficult. Here are your basic options (information that should be easily found on the packaging):[1] X Research source “Works with 1 stage heating or cooling”: Used when you have separate heating and air conditioning units “Works with 2 stage or multi-stage heating or cooling”: Used for heating or cooling units that have designated high and low speeds “Works with Direct Line Voltage”: Used with 110 or 240 direct current power sources to power the thermostat (generally seen in older homes) “Works with 24mV”: Used with fireplaces, floors, or wall furnaces “Zoned HVAC”: Used when both heating and cooling are individually controlled in different areas from the same system
Reading instructions is a total drag, yes. But this is not something you want to mess up! Read them and study the pictures. You want yours to match detail for detail. It’s also a smart idea to always take pictures of the existing wiring before you start.
Some thermostats have a base and sub-base. You need to remove the entire thermostat – all you should be left with is exposed wires and a bare wall, nothing else. If the wires you expose are corroded and there is enough wire length, re-strip the wires. Otherwise, scrape the ends with a utility knife until they are shiny.
With a piece of tape, write a letter on each wire, matching the letter of the connection on the thermostat base. If the blue wire was in connection B, write “B” on the piece of tape, and put the tape on the wire. Label or designate any wires that were loose and unconnected to your thermostat as well. Ignore the colors of wires, except for your own identification purposes. Thermostats wired by non-professionals do not usually adhere to codes, so the colors may not match what they should.
With a piece of tape, write a letter on each wire, matching the letter of the connection on the thermostat base. If the blue wire was in connection B, write “B” on the piece of tape, and put the tape on the wire. Label or designate any wires that were loose and unconnected to your thermostat as well. Ignore the colors of wires, except for your own identification purposes. Thermostats wired by non-professionals do not usually adhere to codes, so the colors may not match what they should.
Pro tip? Wrap all the wires around a pencil. The weight of the pencil is just enough to keep the wires from going anywhere.
If your new thermostat has a mercury tube (that is to say, if your new thermostat is rather old school), your device needs to be completely level or it won’t render accurate readings. Using a level is very important in this scenario and is not just for aesthetic reasons. Make sure you’re drilling holes that match the size of your screws. A 3/16" drill bit is fairly standard. Your thermostat definitely comes with screws, and probably comes with anchors. Make sure to use the anchors, too. They support the system on the wall.
Your new thermostat should have the same corresponding code on the back, unless otherwise noted in the instructions. If you’re at all in doubt, contact a heating and cooling company. Some thermostats are as simple as a two-wire system. Some have 5. If you have empty ports or connections, don’t worry. Your thermostat is most likely fine.
If your thermostat isn’t in a good location (it’s exposed to drafts or heat, which can mess up the readings, or it’s too high or low for you), you’ll need to contact a professional to have wires moved.
And don’t forget to install the batteries! Most systems require 2 AA batteries to work. Make sure the batteries aren’t old, they’re in place, and the polarities are correct
You may need to hit the reset button on your new thermostat. Some will not start until this button is pushed.
It’s not a dumb idea to protect yourself with goggles or gloves, either. If you don’t want anything getting in your eyes or your hands getting covered in gunk, get out the protective gear. And, of course, a shirt you don’t mind smudging with grease or oil.
Place a bucket (or some sort of container) underneath your radiator. You’ll have somewhere between 4 to 8 cups of fluid pouring out, so don’t skimp on the size of your container. At the bottom of the radiator, there should be a draining screw or cap (technically, it’s a radiator drain cock). Twist this to the left, opening it up. Let all the water and coolant flow out. Keep the cap somewhere you won’t lose it.
The body of the thermostat is probably metal with a bit of gold in the center and possible a rubber ring around the edges. It resembles a top or dreidel in shape and size, or, a small plunger. If you’re not quite sure what you’re doing, consult your manual or look up the location online. It’s better to know what you’re looking for instead of poking around and possibly injuring yourself.
Most vehicles have a two-bolt or three-bolt system for the thermostat casing. If corrosion and gunk is building up prominently, clean up the area before you go about adding your new thermostat. A bit of water will probably come out with removal of the hose. This is normal.
Get a pot of water boiling. Insert your thermostat. The thermostat should open at around 190 ºF (88 ºC). Since water boils at 212ºF (100ºC), this is more than enough. If the thermostat doesn’t open in the water (and then close when it cools), you need a new one.
If the area is building up dirt and grime, wipe it down with some cleaner first. You want to maximize the life of your thermostat and not have to deal with this again anytime soon.
Make sure the thermostat is snug and in place. Bolt down the thermostat casing over top of the thermostat. Finger start your bolt and then bust out your pliers or socket wrench and get to tightening. Be careful not to strip the bolts. Replace the radiator hose and clamp. The radiator should be snug on the outside of the thermostat casing and the clamp must be well-tightened.
Once replaced, check for leaks. Your car needs coolant to operate safely. If yours is leaking, you literally won’t get very far.
