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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. We explain how heat anticipators work at HEAT ANTICIPATOR Operation and separately at HEAT ANTICIPATOR Adjustment. we explain how to adjust the heat anticipator on a room thermostat by moving its pointer arm.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman. How to Use a Mini Ammeter to Check Heat Anticipators and Thermostats for Proper AdjustmentWhy do some thermostats include a heat anticipator?
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. Because some controls are used in common on hot water heat, hot air heat, and steam boilers, readers should see these other articles: see BOILER CONTROLS & SWITCHES, and also see BOILER COMPONENTS & PARTS for a detailed list of heating boiler controls, other heating system components, parts such as circulator pumps & draft regulators. If your building uses warm air heat, see FURNACE CONTROLS & SWITCHES. If your building uses steam heat see STEAM HEATING SYSTEMS. Also see Heat Won't Turn Off - Stop Unwanted Heat. How to Connect the 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. How to Make the Correct Current (Amps) measurement at the thermostat heat anticipator
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. What is the Exactly Correct Heat Anticipator Setting when Using an Ammeter?
What do we gain from fine-tuning the thermostat's heat anticipator adjustment?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. Watch out for static cling that can foul up an ammeter reading when measuring a thermostat circuitPrecaution 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. The mini ammeter for adjusting thermostats to work precisely (shown at the top of this page) was produced by and may still be available from T.D. Instruments Corporation, 180 Charlotte St., Rochester, NY 14067 - 716-232-4208. We used model T.D. 2, which operates between 0 and 1.2 Amps A.C. Frequently Asked Questions (FAQs) about testing thermostat heat anticipators & setting the heat anticipatorQuestion: what is the relationship between setting the heat anticipator higher or lower and the resulting room temperature?
Reply:Typically if you set the heat anticipator lower you are narrowing the "gap" or amount by which the heat anticipator anticipates the amount by which heat delivery will "coast" when the thermostat stops calling for heat. In our example photo (left) moving the pinter to the left is setting the heat anticipator to a lower resistance (turn heat off later) and moving the pointer to the right is setting the heat anticipator to a higher resistance (turn heat off sooner). If you click to enlarge our heat anticipator photo you'll see that the settings range from 0.10 to about 2 Amps - a scale quite similar to the mini Ammeter used to fine-tune thermostat heat anticipators based on the circuit resistance (Ohms) and current flow (Amps) as we discuss above. Notice that at the left end of the heat anticipator wiper dial at the lowest setting Honeywell has imprinted the word "LONGER". This means the heat will run longer or cut off later and the room will be warmer when the thermostat turns off the heating boiler or furnace. Details about Heat Anticipator Function and SettingsThe heat anticipator, by warming the thermostat bimetallic spring heat sensor, causes the thermostat to stop calling for heat sooner. The result is that the room temperature will be a bit lower when the thermostat turned off the heating system.
Put another way, because the heat anticipator is basically a resistor that itself heats up the wall thermostat in order to cause it to turn off the heat ahead of the room temperature set point on the thermostat, moving the heat anticipator to a higher setting (typically to the right) is moving it to a position of greater resistance in the circuit. Lower resistance in Ohms, or lower Amps draw, means that less heating of the thermostat bimetallic spring will be caused by the heat anticipator circuit all mean that the heating system will remain on longer before the thermostat reaches the set temperature and turns off the heater. See HEAT ANTICIPATOR Adjustment for details on how to set the thermostat heat anticipator. Also see Definition of Amps, Electrical Current, and Definition of Ohms, Electrical Resistance Ask a Question or Search InspectApediaUse the search box below to ask a question or to search the InspectApedia.com website. Ask a Question or Enter Search Terms in the InspectApedia search box just below. Technical Reviewers & ReferencesRelated Topics, found near the top of this page suggest articles closely related to this one.
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