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AIR HANDLER / BLOWER UNITS
AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
BACKDRAFTING HEATING EQUIPMENT
BACKUP HEAT for HEAT PUMPS
BLOWER FAN OPERATION & TESTING
BOOKSTORE - InspectAPedia
CIRCULATOR PUMPS & RELAYS
CONVECTOR HEATERS - HYDRONIC COILS
COOL OFF HEAT, THERMOSTAT SWITCH
DEFINITION of HEATING & COOLING TERMS
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCT SYSTEM & DUCT DEFECTS
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRICAL POWER SWITCH FOR HEAT
FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON THERMOSTAT SWITCH
FAN, COMPRESSOR/CONDENSER UNIT
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
NO HEAT - FURNACE
ODORS FROM HEATING SYSTEMS
OIL FILTERS on HEATING EQUIPMENT
PULSE COMBUSTION HEATERS
RESET SWITCH, HEATER PRIMARY CONTROL
RESET SWITCH, HEATER REPAIR
RESET SWITCH, ELECTRIC MOTOR
RESET SWITCH, STACK RELAY
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
THERMOSTATS, WATER HEATER
THERMOSTATIC EXPANSION VALVES
ZONE VALVES, HEATING
Thermostat heat anticipator testing & fine tuning procedure: this article explains how and why we fine-tune a room thermostat or wall thermostat by checking its heat anticipator using a mini ammeter.
We describe the use of the T.D. Amps-Check mini ammeter specifically designed for thermostat heat anticipator adjustment.
This mini ammeter gives precise amps readings in the 0 - 1.2A AC range. By measuring the current (amperes) flowing through the thermostat contacts on a call for heat we can adjust the heat anticipator precisely to its optimal setting.
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Since a room heating or cooling thermostat is really just a simple "on-off" switch, some fuzziness needs to be built into the thermostat's control of the air conditioner or heating system, lest it cycle on and off too frequently, oscillating very closely around the set temperature.
The job of the heat anticipator circuit in a wall thermostat is to prevent heating or cooling "overshoot" too far past the set temperature, but to permit some overshoot to prevent system on-off oscillation.
When we serviced heating systems and our clients sometimes complained that the thermostat did not seem to be responding as desired to room temperature.
The thermostat might permit the room to get much warmer, or much cooler than the temperature to which the thermostat was set.
This was a reason to whip out our little ammeter to see what was really going on with the thermostat circuit.
A second reason we'd use this ammeter to check the current draw of the thermostat circuit was to allow proper setting of a heating or air conditioning system control set which was made by a different manufacturer from the one who made the wall thermo sat.
For example, if the air conditioning or heating system control being switched on and off by the thermostat was not one of the ones in Honeywell's list, one of the checks we'd make is to actually measure the heating control circuit ampacity using a special mini ammeter sold just for that purpose, and shown in our photo at left.
Since we no longer service heating systems, we'll give our tool free to a trained heating service technician who'll pay the shipping postage.
How to Connect & Use a Low-Range or Mini Ammeter to Check the Thermostat Circuit and the Heat Anticipator
Usually these are "R" (red) and "W" (white wire) or "R" and "Y" terminals on thermostats.
Just connect the ammeter's leads to the thermostat terminals where you see the red and white wires coming from the heating system are already wired. (You'll have to remove the thermostat cover to perform these steps.)
The current flow (Amps) is read on the meter, and the heat anticipator is set to match the actual current that was just read.
Watch out: T.D. points out that a few controls, such as motorized gas valves, draw more current while operating than when they are in the fully-open position. So if your ammeter shows an unusually high reading (say more than 1.2A) you should hold the ammeter leads on the terminals for an entire minute. By that time the motorized valve should be fully open and you should see a lower AMPS reading. Examples of equipment where you will face this problem include
Watch out: the amps reading made at the room thermostat can also indicate a system or wiring problem: if the meter continues to read current over 1.2A there is probably a system problem, risking damage to the thermostat itself.
Example: thermostat 24VAC circuit reads 0.7A. Set the pointer to 0.7A on the scale as shown in our sketch at left.
This places the thermostat heat anticipator in exactly the right setting for the equipment to which it is attached. Then we simply removed our test leads and re-set the thermostat to the desired room temperature.
When the heat anticipator is working correctly, it prevents too much temperature "overshoot" when the thermostat is turning heating or air conditioning equipment on or off. Ultimately this means that the thermostat will maintain room temperature more accurately and more closely to the "SET" temperature set by the occupants.
Precaution when using this equipment: if the meter is wrapped in plastic there may be a static charge when you unwrap it. Because it is very sensitive, any static charge on this meter (or many other ammeters or VOMs or multimeters) can cause the dial movement to show an erroneous reading. Just wait 5 minutes before using the meter, allowing the static charge to dissipate.
Where to Buy the Mini-Ammeter Amps-Chek® from T.D. Instruments or equivalent low-range high precision amps measuring instruments
Continue reading at HEAT ANTICIPATOR Operation or select a topic from the More Reading links shown below.
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