Reversing Contactor
Mastering Thermostat Replacement
A Thermostat in its most elementary form is composed of three switches.
- The first switch mechanically closes/opens the circuit powering the compressor/condenser fan.
- The second switch immediately closes/opens the circuit powering the indoor blower.
- The third switch immediately closes/opens the circuit powering the heater.
Additional switches may be added to:
- By hand turn the power off to the thermostat, preventing the system from operating
- By hand turn the indoor blower on, overriding the automated blower operation
- Automatically turn a reversing valve on/off in a heat pump
- Automatically turn extra stages or secondary heat, on/off
Logic composed of alterable mechanical or electronic gizmos is combined into the thermostats to instantly determine when the switches should operate.
There are plenty of different configurations for thermostats and many different sorts of systems the must be adapted to control. Replacing a thermostat is not beyond the ability of a DIY home owner, but can be very complex and challenging for an expert in some cases.
Here are some things you have to know.
What type of first heat have you got?
- Heat Pump
- Furnace, gas or oil
- Electric resistance
- Baseboard
Do you have a back-up heat source?
- Heat pump with electric resistance
- Heat pump with furnace (dual fuel)
- Other
How many and what color wires are run to your thermostat and which ones are in use? Thermostat cable comes in many varieties with different numbers and colors of wire. There are standard colour codes, but that doesn't mean they were followed when your system was put in. You will have 3,4,5,6 or 8 wires. A set of wires is run from your outside unit to your thermostat and another wire or set of wired from your thermostat to the inside unit.
- Red is generally power . Some older thermostats don't have or do not use the red wire and might have no power or might be battery powered. If your thermostat has an inbuilt clock it needs power. The red wire may be utilized for another purpose, use caution.
- If you have Red power you will have a negative, ground or common wire
- The Yellow wire supplies power from the thermostat to the compressor and condenser fan. The compressor, outdoor condenser fan and indoor blower must operate at the same time.
- Green is used to power the indoor blower.
- White is used to power the first stage of heat.
- Orange is used to power a reversing valve if you've got a heat pump and the reversing valve is in heating mode with no power to the valve. If you use orange, you will not use blue.
- Blue is used to operate a reversing valve for a heat pump if the heat pump is in cooling mode with no power to the valve. If you use blue, you will not use orange.
- Further wires may be present for second stage heat or other devices.
The power to the thermostat is mostly 24 volts AC. The source of the power is a control transformer located in the outside unit or inside unit or some other place. 24 volts is employed for control because this low voltage is considered safe. Be aware there are some systems that use higher control voltages, so you should usually measure voltage first. Since 24 volts will not operate a huge compressor or motor a relay or contactor is found near to the compressor or motor and the motor or compressor is attached to high voltage by providing power to the relay.
You can see a terminal on the thermostat labeled R1 or R2 or Rc and Rh. These terminals are used when there are two transformers in the system. If there's only one transformer these terminals will be jumpered together. If there are 2 transformers, you need to be careful not to connect the 2 control circuit anywhere in the system.
If you are installing new thermostat wire it's good practice to incorporate a red wire and a spare wire even if you do not need them. They can turn out to be useful.
In some heating systems the indoor blower is not controlled by the thermostat, but is energised by a new control that may bring the fan on when the air has been heated to a snug level.
Before starting replacing a thermostat, ensure you know where each wire goes and what each wire is being used for. Measure the power and the turn the electricity off and secure the switch before beginning work.
We have much more detailed info about Thermostat wiring at Thermostat HQ. Michael Glover is a 40 year vet of the HVAC Industry.
How to Add an Auxiliary Contact Block to Eaton Cutler-Hammer Freedom Series NEMA Contactor
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CUTLER HAMMER STARTER NON-REVERSING CONTACTOR NEMA SIZE 6 CAT# A201K6CA NEW 100% $10,000.00 |
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EATON/CUTLER HAMMER W201K4CF NON-REVERSING CONTACTOR 135A 3P ***NIB*** $5,499.00 |
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Cutler Hammer Eaton A201K6CAZ1 Non Reversing Contactor NEMA Size 6 $3,795.25 |
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CUTLER HAMMER STARTER NON-REVERSING CONTACTOR NEMA SIZE 5 CAT# A201K5CAC NEW $3,200.00 |
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CUTLER HAMMER NON-REVERSING OR REVERING CONTACTOR 3 PHASE CAT# V200M4CJC NEW $3,000.00 |
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Cutler-Hammer VM160CJ Non-Reversing Vacuum Contactor $2,499.00 |
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Cutler Hammer A201K5CAC Non-Reversing Contactor Motor Starter NEMA Size 5 NEW!!! $2,000.00 |
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NIB Cutler Hammer W210MLCFC Contactor Reversing Size 1 $1,700.00 |
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Cutler Hammer W210MLCFC Contactor Reversing Size 1 $1,500.00 |
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Cutler Hammer A50FNO/A50FN0 Nema Size 4 Reversing Motor Contactor/Starter A50F2 $1,512.00 |
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Cutler Hammer A50FNO/A50FN0 Nema Size 4 Reversing Motor Contactor/Starter A50F2 $1,498.00 |
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SQUARE D 8965DPR63V02 HOIST CONTACTOR REVERSING ELECTRIC MOTOR STARTER 8965 NEW $1,149.99 |
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Furnas 44WB3EAJX251 Reversing Magnetic Contactor 24 Volt .50/.60 Hz Series B NEW $1,000.00 |
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ALLEN BRADLEY 505-COD-9 SERIES C SIZE 2 REVERSING CONTACTOR BRAND NEW IN BOX $975.00 |
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SQUARE D 8702 SDO 2 8702SDO2 SIZE 2 REVERSING CONTACTOR w/31063-409-47 COIL, 240 $889.00 |
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New Square D Size 2 AC Reversing Contactor 8702SDO2V02S $800.00 |
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NIB SQUARE D 8965DPR23V02 CONTACTOR REVERSING 3POLE $815.95 |
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New Telemecanique LD5LB130FC Reversing Contactor Breaker Free Shipping $750.00 |
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ALLEN BRADLEY CONTACTOR REVERSING 104-C60D22 $699.00 |
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Telemecanique Reversing Contactor Breaker LD5LC030B 24vac 50hz coil $700.00 |
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TOYOTA FORKLIFT CONTACTOR FORWARD & REVERSE PARTS 21560 $687.00 |
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NEW CUTLER HAMMER SIZE 3 REVERSING CONTACTOR A50ENV0 $650.00 |
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SIEMENS FURNAS 44CF-31AJ 24V/240-600VAC 7-1/2HP REVERSING CONTACTOR CONTROLLER $599.99 |
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Square D size 3 Reversing contactor 600V AC Class 8810 $550.00 |
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Cutler-Hammer Reversing Starter CE15HN3 Contactor A1 $600.00 |
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NIB TELEMECANIQUE LC2 D3211T6 REVERSING CONTACTOR $500.00 |
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Allen Bradley 100-A09ND3 Reversing Contactor w/ Block 195-FA22 & FA20 HUGE LOT! $499.00 |
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SQUARE D NIB 8965R010V02 AC REVERSING HOIST CONTACTOR (M2) $485.00 |
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NIB CUTLER HAMMER REVERSING CONTACTOR CN55GN3AB SZ 2 3P $445.00 |
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Cutler-Hammer C10FN3 Reversing Contactors, Size 4, 135A $425.00 |
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NEW IN BOX SQUARE D CLASS 8965 TYPE DPR23V02 REVERSING CONTACTOR SERIES A $395.00 |
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Allen Bradley Reversing Contactor 104S-C09DJ210B (2803) $397.99 |
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UP TO 2 ALLEN BRADLEY REVERSING CONTACTOR ASSEMBLIES MODEL 8736SB0-4 $399.99 |
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NEW SIEMENS 43CP32A REVERSING CONTACTOR $400.00 |
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Furnas Reversing Contactor 44DA30AG 208-240 Volts Coil New $395.00 |
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Telemecanique Reversing Contactor LC2D5011G6 NEW $400.00 |
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NEW REVERSING INTERLOCK CONTACTOR REPLACEMENT FITS SIEMENS 3TF5222 REV-PBC-3TF52 $399.00 |
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NEW REVERSING INTERLOCK CONTACTOR REPLACEMENT FITS SIEMENS 3TF5622 REV-PBC-3TF56 $399.00 |
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NEW SPRECHER SCHUH CA3-12C-10-24D 3P GE REVERSING CONTACTOR CR5VBL3AZA 24V DC $399.00 |
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NEW SPRECHER SCHUH CA3-23-10-120 3P GE REVERSING CONTACTOR CR5VDA3AZA 120V COIL $399.00 |
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SIEMENS 80 AMP REVERSING CONTACTOR OVERLOAD ASSEMBLY 3RT10463AK60 3RB10461EB0 $379.99 |
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ABB Control Non-Reversing Contactor A63-30 NEW $363.84 |
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Telemecanique LC2-D633 Reversing Contactor $375.00 |
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NEW ALLEN BRADLEY 505-TOD CONTACTOR REVERSING 9AMP $349.99 |
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Joslyn Clark vacuum reversing contactor 3.6kv 160 amp $300.00 |
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CUTLER HAMMER C50EG3 90 AMP REVERSING CONTACTOR SIZE 3 120 V COIL (N7) $325.00 |
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NIB TELEMECANIQUE LP2 D3201BD REVERSING CONTACTOR LP2D3201 575VAC 32AMP $349.95 |
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NEW SPRECHER SCHUH CA3-9C-10-24D 3P GE REVERSING CONTACTOR CR5VAL3AZA 24V DC $335.00 |
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Westinghouse Motor Control A201K1BA Non-Reversing Contactor NEW $327.00 |
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TELEMECANIQUE LC2D32F7 REVERSING CONTACTOR LC2-D32F7 $320.00 |
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ALLEN BRADLEY 100-S 104-C30ZJ22 REVERSING CONTACTOR 600V 30A MAX – NEW $316.00 |
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Allen Bradley Reversing Contactor 104-A38ND3 38 A (3757) $299.99 |
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NEW ALLEN-BRADLEY 100-C60DY10 REVERSING MOTOR CONTACTOR $299.99 |
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Westinghouse A201K2CA model J non reversing contactor 3 pole size 2 110/120V $300.00 |
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Cutler Hammer A201KOCA Contactor Size 0 Non-Reversing $295.00 |
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Cutler Hammer A201KOCA Contactor Size 0 Non-Reversing $295.00 |
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TELEMECANIQUE LC2D65L7 REVERSING CONTACTOR $310.00 |
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Westinghouse W201K2CF non reversing contactor 3 pole NEMA size 2 120V coil $300.00 |
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43312 Reversing Contactor NEW-NO BOX $309.95 |
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NEW SIEMENS 43CP32AF REVERSING CONTACTOR $300.00 |