Tag: controls


As a technician you most likely know some customers who still have an oldie thermostat (you know, those old mercury bulb things, like the round Honeywell CT87 and such).  Keep in mind those usually have an adjustable heat anticipator.  If you’re newer in the field  you may not have seen or worked with those very much, or even not at all.  They can seem confusing at first (why is it set with amperage? What amperage? How am I actually adjusting this???) but actually are quite simple to work with.


First of all, I hear you thinking “do you actually need to adjust that?  I mean, is it going to make that much of a difference?”  Honestly, in most cases, no, it won’t make a big difference.  But it’s no reason to ignore it.  And when it actually does make a difference, you will want to know how to adjust it properly.


Here’s a hypothetical story: you just changed a system, let’s say converted from a 30 year old oil furnace to a brand new condensing gas furnace.  The homeowner just loves their old, simple, ‘’I-just-have-to-turn-it-up-or-down’’ thermostat and won’t upgrade it to a modern digital one.  And hey, it still works fine, so why bother.  Then, a few days later, you get this service call:  ‘’that new furnace you guys just put in, it doesn’t work right!  It keeps starting and stopping every 5 minutes! (or) It stays on for too long and overshoots the set temperature by a whole degree!’’  (and the line everybody loves to hear): ‘’It didn’t do that with my old furnace!  It’s that new one, you sold me defective garbage equipment!!!’’


Okay, it doesn’t happen like that all the time, but I’m sure you’ve heard of similar stories.  Now, to focus on the problem.  I’m writing this tip about heat anticipators, but please don’t assume that’s going to be the issue whenever you get this kind of service call.  I am merely reminding you that it is one of the many possible problems.  So let’s say everything else is normal, no faults occurring during furnace cycles, no airflow issues, proper system sizing, etc.  There’s a chance a very poorly adjusted heat anticipator will make a significant difference in cycle time.  After all, it’s what it’s designed to do.


In short, the anticipator is simply a resistor built in the thermostat that is in series with the heat call low voltage circuit, i.e. the “W” terminal.  That resistor generates a tiny amount of heat to preheat the bi-metal and end the furnace cycle a little bit earlier, anticipating the residual heat from the furnace and fan off delay to cover the gap in temperature and avoid overheating the space.  Now, even though it’s a resistor, you don’t set it by ohms.  You set it by amperage.  The amperage drawn by the heat control circuit.


Now it takes a little bit of effort to get that measurement properly, but it is quite simple.  First of all, you need to remove the anticipator itself from the circuit when checking the control’s amp draw!  All this means is you need to remove the thermostat from the circuit by twisting together the R and W wires at the thermostat.  This will, obviously, give you a constant call for heat.


Now the amperage you need to measure is typically very low, no more than half an amp in most cases, sometimes much lower.  So, in order to get a more precise reading (unless you have a super sweet meter that gives you precise readings in the tenths to hundredths of an amp range, this would be done in series instead of with a clamp) you should proceed as follows:  get a nice very long piece of thermostat wire, which you will repeatedly wrap around your meter clamp, so it goes through it 10 times.  Then connect that wire to your W wire from the thermostat on one end and to the W terminal on your furnace control on the other end.  Simply put, just extend the W wire so that you have enough to wrap it around the clamp ten times.  Then turn the power on and let the furnace cycle begin.  Wait until all the relays and components are energized (on a typical gas furnace you will see the greatest amp draw coming when the gas valve is energized), then take your reading.  Divide it by 10, and you have your heat anticipator adjustment value.  Simple as that.  For example, you might read (completely arbitrarily) 2.40 Amps on your meter with ten wraps of wire.  Which means the control actually draws 0.24 Amps, so you will need to set your heat anticipator to 0.24.  It is recommended to insert the tip of a pen or something similar in the slot to gently slide the needle to the desired setting.  And this procedure, by the way, is still explained in modern install manuals.

Honeywell also gives a basic guideline for different heat types


To further adjust cycle times if the actual setting doesn’t seem to work quite right, you may change it accordingly: higher amperage setting = longer cycle time lower setting = shorter run time.  I wouldn’t stray too much from the ‘’proper’’ setting, however.



— Ben Mongeau

I got this question via email (edited slightly for length)

Some things I’ve done because I’ve been taught to do them yet I don’t know why I do them. One of those things is putting a jumper between w1/e and w2. Sometimes, in the case of a Goodman for example, I’ve been taught to combine the brown wire along all the whites at the air handler. Do you mind just clarifying the whole situation with w1/e jumped to w2? And also maybe x2 on some stats? Thanks for your help.
— J

Back in the early 2000’s when I was the lead trainer for another company some of the most common miswiring issues has to do with electric heat. So much so that I created a bunch of different wiring diagrams with a fancy program called “Microsoft Paint” to illustrate how to wire different combinations of equipment. Here is one of them.

In older thermostats (older than the diagram shown here) there were no installer setup programs in the thermostat where you could designate the type of system the thermostat was connected to. Each terminal performed a particular universal function and you would configure the operation based on how you wired it up. Which terminals you connected where, which you left open and sometimes, which ones you jumpered out.

So first, let’s give a quick look at the meaning of each terminal

W – When you see a W terminal it just means heat. Usually, you will only see W when the control only has one stage of heat

W1 – Means first stage heat. In a heat pump first stage heat is the same as the first stage cool. It just means the contactor/compressor is turning on. Whether that is heat or cool is actually dictated by whether or not the O/B terminal is energized. This is why on many old thermostats you would jumper Y1 and W1 in a heat pump application.

W2 – Means second stage heat. This could be the first stage of heat strips in a common southern heat pump, the gas furnace backing up the heat pump in a modern “hybrid heat” application or just a second heat strip bank in the case of a straight electric system. W2 is generally called on based on a temperature differential between setpoint and space, outdoor temperature and/or run time.

W3 – Is just the next stage of heat after W2

E – Is emergency heat, usually just a way to manually drive on what would normally be the secondary form of heat without stage 1 heating.

Emergency heat only makes sense when there is some sort of secondary heat source and really even then, it only helps if the secondary heat source is sufficient to heat the space as in the case when the secondary is a furnace, Hydronics or a large heat kit. In Florida, most of our units have 5KW auxiliary heat which will never be sufficient to heat a home in an “emergency”.

Many of these other terminal designations are a holdover from a time when all the controls in the thermostat and defrost board were electromechanical, and much of it was for indication/trouble lights and some of it was for the thermostat to be able to perform staging based on outdoor temperature due to the fact that run time logic was not available. So for your X2 question, have a look at the thermostat and diagram below.

In the modern thermostat, they have usually relegated these staging configurations and terminal designations into the installer setup and every thermostat is a little different. In general, in the south we jumper w2 to E because they truly are the same, in some cases, this does nothing, in others, it just ensures that the aux heat comes on quicker if the user chooses emergency heat.

Are there some cases where emergency heat could be totally different than aux heat? I’m sure… I have just never seen one personally. Like usually, it all comes down to knowing your particular piece of equipment and your controls, reading the installation instruction is a good first step.

— Bryan



Back in the “good old days” controls were all analog and mechanical which simply means that they acted in a directly connected and variable manner based on a change in force. Both pneumatic (air pressure) or hydraulic (fluid pressure) systems are examples of mechanical, analog controls. When pressure increased or decreased on a particular device it signaled a change in action on another device like a pump/valve etc…

In the HVAC/R industry, we still see these types of controls with a TXV being a common example. The TXV is controlled by pressures in the suction line, bulb and spring to set the outlet superheat. These forces are all mechanical without electrical inputs or specific “data points”. The feedback from these forces is in constant tension to output the proper amount of refrigerant to properly feed the evaporator coil.

Digital vs. Analog

As controls have changed from mechanical to electrical we now have systems that are controlled by analog electrical signals and digital electrical systems. Analog is simply a varying electrical signal (either voltage or amperage) that signifies changes in a system or device. A digital signal means data encoded into “digits” which can be communicated using many different computer languages, rules or protocols (these all mean essentially the same thing). In digital controls the “signal” can include a combination of voltage, amperage and On/Off changes to communicate between devices.

So what about 4-20ma?

When the industry started to change over from mechanical to electrical they created a protocol (set of rules) that controls could use that would still function in a similar way to the old pneumatic controls. They decided that the range would be  4ma(milliamps) as the bottom reference of any sensor and 20ma would be the top reference. If you were setting up a sensor to indicate the fluid level in a tank you would set the bottom output to 4ma (meaning empty) and the top output to 20ma (meaning full).

In the case of a pressure transducer, you set the top range to the max rating of the sensor to 20ma and the bottom pressure reading to 4ma… you get the point.

ma controls are great because of their simplicity and ruggedness. You supply power to a “sensor” (Actually a sensor/transmitter to be exact) and based on the measurement the sensor reports to the transmitter that produces a milliamp signal. This signal is connected to an input on the control that measures the amperage and converts that to a reading.

Because amperage is the same at all points in the circuit the 4-20ma circuit is not impacted by voltage drop or interference like a voltage sensing circuit. Because the “bottom” of the scale is 4ma the control can also sense the difference between an “out of range” condition below 4ma and an open circuit.

The downside of a 4-20ma control is that each device requires it’s own conductor. In digital controls, many devices can be controlled by a single conductor set or “trunk” making it much easier to route, configure and manage complex controls.

Testing 4-20ma Circuits 

There are two different ways to measure milliamps. One is to use a special milliamp clamp called a “process clamp meter” that allows reading the amperage without disconnecting wires. These meters are expensive and it is unlikely that a typical HVAC/R tech will have one.

The more common way it to use alligator clips on a quality meter set to the milliamp scale and connect in series with the circuit. this means you will need to disconnect a wire or terminal and put your meter in the path. This is the same way we test microamps on a gas furnace flame sensing rod only using the milliamp scale.

— Bryan


This tip was created by Jason Pinzak and originally posted on the HVAC Technician’s Facebook group. It is reposted here with permission from Jason. Thanks!

Contactors are useful in commercial and industrial applications, particularly for controlling large lighting loads and motors. One of their hallmarks is reliability. However, like any other device, they are not infallible. In most cases, the contactor does not simply wear out from normal use. Usually, the reason for contactor failure is misapplication. That’s why you need to understand the basics of contactors.

When someone uses a lighting contactor in a motor application, that’s a misapplication. The same is true when someone uses a “normal operation” motor contactor for motor jogging duty. Contactors have specific designs for specific purposes.

When selecting contactors, you’ll use one of two common standards: NEMA or IEC. Both match a contactor with the job it has to do, but they do so in different ways.
The NEMA selection process always results in a choice of a contactor you can use over a broad range of operating conditions. For example, you could use a NEMA Size 5 contactor to run a 50-hp motor operating at 230V or a 200-hp motor at 460V.

Using IEC standards, however, you can size contactors very close to their ultimate capabilities. In many cases, this precision allows you to predict how long they’ll last. For example, an IEC-rated contactor may run a motor that draws 40A at full load. In that duty, it should last for more than two million operations. But, if you used it for consistent jogging and plugging, you’d have to replace it after just a few thousand operations.

Since a contactor should last for years, don’t automatically replace one that fails with an identical unit. Instead, take a few moments to see if there is an obvious problem. A contactor really has only two basic parts: the contacts and the coil. The coil energizes the contactor, moving the contacts into position. The contacts transmit the current from the source to the load. Heat can destroy either of them, so take a good look at both.

Contacts will overheat if they transmit too much current, if they do not close quickly and firmly, or if they open too frequently. Any of these situations will cause significant deterioration of the contact surface and the shape of that surface. Erratic operation and failure will be quick. To check the contacts, just look at them. Some minor pitting (see photos) as well as a black oxide coating is normal, but severe pitting or any melting or deforming of the contact surface is a sure sign of misapplication. Replace contacts with such symptoms.

Coils can overheat if operating voltages are too low or too high; if the contacts fail to open or close because of dirt or misalignment; or if they have suffered physical damage or experienced an electrical short. Coil insulation degrades quickly when it gets too hot. When it degrades, it will short out (and blow a fuse) or just open and stop operating.

To check a coil, measure the ohms across the contactor coil. Infinite resistance means the coil is open. A shorted coil will still often register significant resistance and can be confused with a good coil . If you happen to have a matching contactor nearby, compare the two coils. The shorted coil will usually have significantly lower resistance than the good one but a compromised coil can alos have a higher resistance. If the difference is significant, replace it. Replacing the contacts or coil often means replacing the whole contactor. But no matter what you replace, compare the NEMA or IEC rating with the job the contactor will be doing. If you match it to the application, it should last a long time.

— Jason Pinzak

P.S. – Here is another good article on the difference between IEC and NEMA rated contactors

Modulation motors are not often seen in residential equipment but are used quite often in commercial and industrial applications on many different types of equipment. I see them primarily on larger burners as a means to control the fuel firing rate, but they are used to control water flow through heating coils, the water level on cooling towers, and countless other applications. Anytime you need to control the flow of a medium (gas, water, air) and have valves or dampers that modulate flow; a mod motor probably has been used for it at some point. The more basic mod motors have been around for a long time, and in many applications have been abandoned for newer and more precise control apparatuses, like servo motors. But there are still a ton of them in the field. I replaced three this week, as a matter of fact. So I thought it fitting to share some information on them.

Here is your basic mod motor. As the label indicates, the voltage required to control the motor is 24 VAC. This is most common on mod motors I typically work on, but there are other control voltages utilized in different applications. 2-10 VDC, 4-20ma, and other setups are fairly common, but those get more complicated, and I want to keep this as simple as possible, so we will focus on 24 VAC.


On the side of the motor, there is a square shaft end. This is the connection point by which the motor actually changes whatever it is controlling. The motor pictured above came off of a 350 horsepower Superior brand boiler with a Gordon-Piatt burner. The shaft end connected to a linkage arm, that linkage arm connected to a gas butterfly valve and an air damper which controlled primary combustion air. As the motor stroked open, it opened the gas valve and air damper simultaneously, therefore increase the firing rate/size of the flame. As the motor strokes closed, the firing rate is decreased. This motor also contains high and low end switches. The low fire end switch being normally closed ( closed when the motor is in the minimum position), and the high fire switch being normally open and closing when the motor reaches the maximum open position. The end switches are used in industrial burners to prove that the valve is functioning to the burner controller. Generally, the motor moves to the fully open position during per purge/prelight off  and then back down to the minimum open position during light off. If the motor does not open or close the proper end switch at the correct time, the burner control will not allow the sequence of light off to continue, and go into a lockout. Not all mod motors contain high and low end switches, but many do and they do fail. I’ve replaced 5-7 over the last year.

The 24V style motors are often supplied with a transformer inside of the motor housing, but that isn’t always the case. The load side (24 V/ Common) wires to the T1 and T2 terminals on the motor, as shown in the diagram above. The other terminals typically used are R, W, and B. These terminals then connect to some variable resistance controllers. I am used to calling this type of controller a potentiometer, and I believe that is sufficient. As I am primarily a boiler guy, I will look at it from a boiler guy perspective. The common potentiometer type modulation controls I see monitor steam pressure inside of the boiler. They contain the same terminals as the modulation motor ( R, W, and B), and the terminal on the motor gets wired to the correlating terminal on the controller. The motor works off of a difference in resistance through the controller. Less resistance through the R and W terminals on the modulation controller causes the motor to drive to the minimum (closed) position. Less resistance through R and B causes the motor to drive to the maximum open position. As steam pressure rises and falls, the modulation controller changes in resistance through the three terminals. This is how the motor knows what position to be while the burner is firing.


Troubleshooting a modulation motor is fairly simple. The control voltage is necessary for the motor to do anything. If control power is not present between terminals T1 and T2, then the transformer supplying the power should be checked. Transformers are checked by voltage on the line side and the load side. The transformers supplied with the motors are 120 VAC line to 24VAC load. If the line voltage is not present, then we need to determine why. If 120V is present, but no 24v on the load side, then that would indicate a failed transformer. Transformers don’t fail for no reason very often, so the control side of the circuit should be checked for shorts and grounds before the new transformer is installed, or you may run the risk of the blowing the new transformer when the power is restored. Trust me, I speak from experience. If control power is present at T1 and T2, removed the wires from the R, W, and B terminals. A jumper from R to B should cause the motor to drive open, and a jumper between R and W should cause it to drive closed. Some motors contain a spring that causes the motor to close when power is removed, so keep that in mind when troubleshooting. If the motor doesn’t open or close when jumpered, and the correct control power is present, well then you have yourself a bad motor. If the motor works properly when jumpered, but not in normal operation when connected to the control circuit, then there is some issue with the components controlling the motor. Some of these systems can be quite complex, so if you end up in this situation, good luck. You may need your thinking cap.


Any modulation motor you will encounter will operate the same. Control power is required, and some input to cause the resistance change needed for the motor to open or close. If you encounter issues with one, the basic motor troubleshooting techniques should be the same. It doesn’t matter if it’s on a boiler, cooling tower, water tempering system, or anything else.


— Justin Skinner

You can find more info on the Honeywell Modutrol line HERE


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