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COOL OFF HEAT, Thermostat Switch
DEFINITION of HEATING & COOLING TERMS
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DUCT SYSTEM & DUCT DEFECTS
ELECTRIC MOTOR OVERLOAD RESET SWITCH
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FAN, AIR HANDLER BLOWER UNIT
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FAN CONVECTOR HEATERS - HYDRONIC COILS
FAN LIMIT SWITCH
FLOODED HEATING EQUIPMENT REPAIR
HEATING LOSS DIAGNOSIS-BOILERS
HEATING LOSS DIAGNOSIS-FURNACES
HEATING SYSTEM INSPECT DIAGNOSE REPAIR
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
MANUALS & PARTS GUIDES - HVAC
NO HEAT - BOILER
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ODORS FROM HEATING SYSTEMS
OIL FILTERS on HEATING EQUIPMENT
PULSE COMBUSTION HEATERS
Reset Switch - Heater Primary Control
Reset Switch Broken - Quick Repair
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
THERMOSTATS, WATER HEATER
THERMOSTATIC EXPANSION VALVES
ZONE VALVES, HEATING
Room thermostat calibration & accuracy guide: this article explains why a room thermostat may not be responding correctly to the actual room temperature.
Factors that affect the room thermostat's behavior include is location in the building, for some models how level the thermostat was installed, the thermostat's heat anticipator adjustment, even dust and debris in or on the thermostat.
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Where to Locate & Mount a Room Thermostat & what spots to avoid
Locate the room thermostat at about chest height on an interior wall, in a location where the thermostat won't be affected by drafts or other unusual temperature conditions.
Good thermostat locations are
As Carson Dunlop Associates' sketch (left) explains, there are a number of places where you should not locate the room thermostat.
Bad Room Thermostat Locations
Don't locate the room thermostat in these locations:
Yes for Older Mercury Bulb Switches
That's because the coiled bimetallic spring has to move that mercury bulb to a tipped position to turn the heating or air conditioning system on or off in response to room temperature.
When we found a thermostat that did not heat a room accurately to the called-for temperature, we'd take a look to see if it was installed out of level before looking further.
Because the "set" range on these thermostats may have had a lower-end of 55 deg .F., when we wanted the thermostat to maintain a building at a temperature lower than the minimum that the thermostat dial provided, we just tilted the whole thermostat backing plate on the wall in the proper direction to shift the operating range of the switch.
No for Newer Solid State, or Digital Room Thermostats
Newer thermostats that rely on other sensor and switch designs do not have this sensitivity to being out of level and some (such as the 3M-22 thermostat) note in their installation instructions that the thermostat does not have to be level.
Our photo (above left) illustrates the red (R) and white (W) wire connections in a simple two wire heating control thermostat hookup using the Honeywell RTH2300/RTH221 series programmable wall thermostat.
Because some controls are used in common on hot water heat, hot air heat, and steam boilers, readers should see these other articles:
If your building uses warm air heat,
If your building uses steam heat see STEAM HEATING SYSTEMS.
This article is part of THERMOSTATS our article series Guide to Finding, Using, and Adjusting Thermostats for Heating & Air Conditioning Furnaces & Boilers, Heat Pumps or Electric Furnaces or Boilers. This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.
Reader Question: the A/C blower is not working properly in response to the thermostat
A friend's a/c unit has the blower fan that will only work in auto, it will not work on manual. On the other hand, even when you turn the unit from cool to off, the blower still remains on. The only way the blower will turn off, is to turn the fan to manual. He changed the thermostat, and the unit will cool to the desired temp and kick off, but you can't turn the fan off on your own unless you turn it to manual. Anyone ran into this before? - John
Reply: check thermostat wiring connections against the schematic for your unit and see these standard wire color codes
The wiring to the unit depends on if you have a heat pump, or straight a/c unit. It also depends on how the installer has wired the thermostat. With the heat pump, the red is power, the yellow is for cooling, the white is for heat, the green is for the fan, the orange is for the reversing valve, and the blue is usually always common.
Again, you will have to check to see how the installer has ran the wires from the thermostat. If you have a a/c only unit outside, you will only have a red wire, and a white wire coming form the inside unit, to the outside unit. These will go on the contactor to send 24 volts to the coil to pull the contactor in. These are the traditional wiring schematics, again, check the thermostat to see if this is the case with yours. - Bryan
Also see THERMOSTAT WIRE CONNECTIONS where we provide lists and tables of color codes and wire connections for thermostats in various uses.
Question: How do I Calibrate my Thermostat
How to calibrate the thermostat?My temp reads 4 degrees lower than my set temp,in AC mode. - NC
Question: how do I fix a thermostat that I have to set lower than the level of heat I want?
My traditional honeywell simple dial-type thermostat on the wall has two pointers and two temp. scales. However I have to set it on 60 degrees to get heat temp to 70 degrees.
Reply: check these reasons for a room thermostat that keeps calling for heat
On most two-scale room thermostats, one scale reads the current or actual room temperature while the other scale is the set temperature - and is adjustable. When you move or adjust the thermostat to call for a different room temperature you will see the scale pointer move to your new setting on the "set" scale.
Remember that a thermostat is just an "on-off" switch that turns heating or cooling ON or OFF in response to the actual room temperature and the desired or "set" temperature you've specified. Make sure that your thermostat is properly set - to "Heat" mode with the fan switch set to "Auto".
You are describing having to set the thermostat lower (60F) than the desired temperature (70F) to get the proper level of heat in your home. In other words, you say that the room gets too hot - hotter than you asked-for. Here are some things that would cause that problem:
Keep us posted, what you learn will help other readers.
Question: heating thermostat seems to show wrong temperature
My heater's thermostat is showing wrong temp. At off setting , it shows the room temp at about 80 when it feels like 60 degree in the house. I tried removing and putting batteries again but doesn't solve the problem. Do I need to replace it? - P. 1/2/2013
You might, but first check the thermostat's room temperature reading (not its SET temperature reading) against the actual room temperature - use a room thermometer; Then be sure the thermostat is set to HEAT mode and make sure that the SET temperature is above room temperature. Then heat should run until the sensed temperature at the thermostat turns it back off; See the next Q&A for more details.
Question: why do we have to turn our heat up higher than previously just to get warm
Our heating and air unit is roughly 8 or 9 years old. When we first moved here (6 years ago) we kept the air set on 73-74 during the summer months. We were comfortable. Now, we have to keep it up to 79-80 and we still feel like the house is too cold. We had the unit checked out last year ( because we started having double and triple utility bills) and the guy said it was fine. Could this be thermostat problems? I don't really feel that the unit runs more than it should though. - Rachel 8/22/12
First, are we looking at the same outdoor temperatures as previously? If not, if it's colder now than previously, the problem could be with your home's rate of heat loss - bad insulation, leaky windows &c.
If weather conditions are the same, then we have some other questions to ask: you don't say if your heat is from hot water or forced warm air. In either of those systems, even if the equipment is running as before, you could have a simple maintenance problem like a clogged air filter or air bound radiator that's the problem. I'd need to know more.
Continue reading at TEMPERATURE RESPONSE of Room Thermostats or select a topic from the More Reading links shown below.
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