Category: Tech Tips

Most techs and installers know that drains need to be pitched. I use the rule of thumb that drain lines should generally be pitched 1/4″ per foot of horizontal run. One thing that can easily be forgotten in pitching wall penetrations when drilling. It’s as simple as drilling with a slight upward angle if drilling from the outside or slightly downward from the inside. The goal is to have the outdoor side lower than indoors both to assist in draining system condensate and to prevent exterior moisture from running into the building. You will also want to make sure that the drain doesn’t get run on top of copper, or go up and down for any other reason. This is especially common in Ductless systems with flexible drains. Keep that pitch moving the right direction from start to finish and all will be well. — Bray.


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

We had a really great conversation on the HVAC School Facebook Group about some belt tension best practices and it turns out that even a lot of really smart and experienced techs are not aware of all the factors related to belt tensioning.

Myth #1 is that amperage is used to set belt tension. Now don’t get me wrong, checking amperage before and after changing belt tension is an excellent practice to ensure you are not binding the bearings from over tension, it does not tell you whether or not the belt is at optimum tension.

I think Browning summarizes it best in this statement from their Browning tool box technician app

Ideal tension is the lowest tension at which the belt will not slip under peak load conditions

Getting a belt too tight shortens the life of the belt and bearings and can cause high amperage. Leaving a belt too loose will shorten the belt life and result in loss of airflow and noise.

Many techs confuse the sheave adjustment, designed to alter the pulley ratio and the airflow with the belt tension adjustment. These are not the same thing and serve separate purposes.

The adjustable sheave allows the pulley faces to adjust closer or further from one another, resulting in a belt that rides closer to the hub when looser (halves further apart) or closer to the edge when tighter  (halves further separated) THIS ADJUSTMENT IS FOR FAN SPEED ONLY NOT TENSIONING

A properly tensioned belt should not slip significantly when starting, it should not be noisy and it should not bounce around. If you tighten the belt check the amps before and after and the motor should not overamp.

The correct tension method is to get the belt close to the correct tension by feel with a deflection of 1/64 of an inch for every 1″ of distance between the two pulley centers. You can then use an app or a chart like THIS ONE to find the proper force to generate this deflection.

You would then use a belt deflection tool like the one shown above to test the deflection force required and adjust accordingly. The video below demonstrates this.

I like what Jeremy Smith stated in the group “Belt tension has less impact on motor amperage than pitch diameter of the sheave and how that affects total airflow. Use the Emerson tool and the app (or paper chart if you’re all stone age) Record tension and other data (sheave diameter, center to center length, rpm and proper tension) on the blower housing.”

Check those belts during commissioning, maintenance and service and change them as needed.

— Bryan


Depending on what segment of the business you are in and what area of the country you work, you either work on pump down solenoid systems all the time or YOU HAVE NO CLUE what they are.

A liquid line solenoid is just a valve that opens and closes, it has a magnetic coil and depending on whether the valve is normally open or normally closed it opens or closes when the coil is energized.

If you work on refrigeration or straight cool units up north, you are likely very well acquainted with “pump down” solenoids. If you do residential HVAC in the south you may have never seen one.

You know that you pump down a system by closing the liquid line? That’s all a pump down solenoid does. It closes when the system is running causing the system to pump all of the refrigerant into the condenser and receiver (if there is one).

The trick is that in order for it pump down the compressor needs to be running  and then it needs to SHUT OFF once it is done pumping down. This means to need a good, quality, properly set low-pressure switch near the compressor to shut it off when the suction pressure gets low enough but not TOO low. The goal is to get all the liquid pumped into the condenser not to pump down to zero.

There are a few benefits of a pump down solenoid. First, it helps prevent liquid refrigerant migration down the suction line into the compressor. When liquid refrigerant migrates into the compressor it dilutes the oil and can cause a “flooded” start.

The other cool thing is you don’t need any Low voltage controls between the indoor and outdoor unit (in some cases). The solenoid is in the liquid line near the air handler inside, so by opening the valve the suction pressure increases and the compressor turns on and when it closes the compressor pumps down and shuts off.

Obviously, this would not work on a heat pump system because in heat mode it would attempt to pump down into the indoor coil which would not work. They also won’t work in most cases when you have complex or proprietary controls.

In some cases the liquid line solenoid is not used to “pump down”, it simply closes during the off cycle preventing refrigerant flow and migration in that way.

So… there are places where a liquid line solenoids make sense and applications where they don’t but they are fairly simple and easy to understand.

— Bryan

I know I’m gonna get some eye rolling here but it needs to be said.

When we teach electricity to new techs we use a lot of “water” metaphors. We talk about volts like PSI, amps like flow and Watts like GPM. Even the word “flow” gives us a vision of water moving.

Then we talk switches and circuits and we say “open” to mean no path / no flow and “closed” to mean a path or flow.
That’s the opposite of water…

With water, we “open” the tap when we want flow and close it to stop the flow.
With a switch, we “close” when we make a circuit and we “open” when we break a circuit.

Someone pointed out to me that describing an “open” switch or circuit like a drawbridge may be better. Cars (electrons) can move when the bridge is closed and cannot move when the bridge is open.

It struck me that this water metaphor may be one reason newbies struggle to grasp relays.
Or maybe I’m just overthinking it.

— Bryan

First I want to give credit where credit is due. This post is made possible by the fantastic demonstration video by Neil Comparetto that I embedded below.

Before you get bored and stop reading I want to give some conclusions. Ice can form in a vacuum, but I still advise pulling a fast, deep vacuum. Now… keep reading to see why.

The statement that is often made by techs is that pulling a vacuum “too quickly” can result in freezing of the moisture inside the system and reduction of evacuation speed. This conversation usually occurs when another tech is demonstrating a SUPER FAST evacuation, or by a tech who is advocating for the consistent use of triple evacuation.

Neil’s video proved that pulling a deep vacuum quickly can result in freezing with even a small amount of liquid water present. He also demonstrated that this is possible with a typical HVAC hookup and that it can pull down to 500 microns with substantial ice present. This was done in 50 degree shop, with a glass jar (insulator), with relatively low internal volume, pulled down using a vacuum pump direct connected with large hoses.

So he proved that under certain circumstances, ice can form and cause a real problem with evacuation speed and even trick a junior tech into thinking they pulled a proper vacuum when they did not.

Now before you get too excited

In a typical system with larger internal volume than a jar this experiment doesn’t replicate the same results unless of course the ambient temperature is already near or below freezing.

So what causes this (Water freezing under vacuum) and how do we prevent it?

Water, like all substances, changes state due to the molecular density and configuration based on the pressure surrounding the molecules and the temperature of the molecules (average molecular velocity). When we pull a vacuum on water there are two opposing forces, on one hand we are DECREASING the pressure which leads to evaporation and then boiling, but as the water boils it begins to lose heat because that molecular energy of the highest velocity molecules are being evaporated and removed by the vacuum pump, thus reducing the average molecule velocity (temperature). The key reason why it can freeze in these experiments is because the heat rejected through evaporation / boiling is significantly higher than the heat ADDED through the sides of the jar which is why it starts by flashing, then boiling, then back to liquid then freezing. You are WATCHING the change in energy state in real time as the available heat in the jar and added through the walls is overcome by the heat REJECTED from the boiling liquid and out the pump.

Now, if the pump was left on the ice long enough, the ice would eventually all SUBLIMATE (change directly from solid to vapor) but the rate at which that would occur is based solely on the amount of heat being added to that ice through the walls of the jar. This addition of heat is equal to the differential in temperature between the ice in the jar and the temperature around the jar.

The deeper the vacuum pulls the colder that ice will get, which will increase the differential between the ambient around the jar and the ice temperature inside.

If we hit the jar with a heat gun, the ice would melt quickly because we are ADDING a huge amount of heat very quickly. In the same way, if the ambient temperature in Neil’s shop was higher or if the vessel was made of copper (conductor) instead of glass (insulator) it would be less likely that ice would form and if it did form it would sublimate more quickly.

Here are my current conclusions based on this video (and many others), good science and practical field experience

It becomes increasingly more important use a heat gun on components and sweep nitrogen as ambient temperatures drop

  • Liquid water inside a system should be exceptionally rare, follow good copper handling practices and don’t work with open copper in the rain.
  • When the internal volume of the system you are evacuating is very small it would be easier to create ice (ice machines, ductless linsets etc…) use more caution in these circumstances by employing triple evacuation / breaking the vacuum with nitrogen / sweeping with nitrogen.
  • Most important is to valve of the micron gauge from the pump and watch for rapid increases. If you have ice you WILL see and quick increase when the micron gauge is isolated from the pump in the system.
  • Use a quality micron gauge that can show you a decay / leak rate so you can easily be aware when there is an issue.
  • When you are pulling a vacuum on most systems, during warm ambient conditions you are RARELY if ever going to make ice in a system under vacuum.
  • The conclusion is NOT to pull a SLOWER vacuum, it is simply to use heat and breaking the vacuum with nitrogen to get the moisture removed.

Here is the video-

— Bryan

There are many great diagnostic tools available to the service technician today, but I shaven’t found a tool as versatile than the simple isolation diagnosis.

There are many ways this concept can be applied but let’s start with some examples so you get what I mean.

Low Voltage Short Circuit Isolation Diagnosis

You arrive on a no cooling service call at a home and you find the system is off and doesn’t respond to any thermostat settings. You check the breaker and the condensate switch at the furnace by force of habit and look at the door switch, everything looks in order so far.

You take a look at the 3A low voltage fuse and SURE ENOUGH, visually blown.

Now there are many schools of thought of how to proceed from here but I prefer to use logical possibilities and process of elimination before starting to tear everything apart.

First,  look at any possible rub out points on low voltage wires in the furnace, visually inspect the safeties, go outside and check the control wire both inside and outside the condensing unit and ESPECIALLY wherever wires run across copper tubing. If you find nothing at these common failure points I will pull open the thermostat there and check that it’s wired correctly with no exposed copper.

You will notice that I didn’t just “replace the fuse”, because science and experience has shown me that fuses don’t just fail open on their own.

If I still find nothing then the “logical possibilities” part of the diagnosis has ended and we move into the isolation diagnosis part of our testing.

Some techs prefer disconnecting all the low voltage wires at the furnace and ohming them one at a time to ground and common at this point. Sometimes this works but I prefer to let the system work for me rather than pulling apart all the wires at this stage.

I replace the blown fuse with a 3a re-settable fuse / breaker like the one shown above with the thermostat off in all modes (to keep from wasting fuses). I then close the door switch and see if the fuse blows, if it does not then we can determine that there isn’t a continuous short circuit in R.

I then use a jumper wire and connect each switch leg (G,Y,W,O,W2,Y2 etc…) to the R terminal quickly and see if any of them trip the fuse or throw a spark (remember this is 24v it’s not going to hurt you). Often you will find the circuit with the short just that simply and then you can further isolate until to find the exact part of the circuit causing the issue.

Let’s say the Y circuit is the one blowing the fuse, you can then separate the two wires going to the condenser and the thermostat and tap one side at a time to R, if the conductor going outside is the one throwing the big spark / blowing the fuse then that is the direction to focus. You then go outside and disconnect the Y wire at the condenser wire nut or terminal block. If the short continues you know it is in the wire between the condenser and the furnace and not in the condenser. If it continues then you know it is in the condenser or in the contactor itself.

Shorted Compressor Isolation Diagnosis

Compressors shorted to ground or “grounded” is a pretty common diagnosis in the field and leads to an expensive compressor or system replacement. It’s important that we get that diagnosis correct and take away all the guess work so I use a combination of diagnostic tools and isolation diagnosis to ensure I never get it wrong.

When I walk up to a condensing unit and it has a tripped breaker, the first thing I do is reset it and see what happens…


The breaker tripped for a REASON and every time I reset that breaker I run the risk of creating a major arc. If that short is inside the compressor I add carbon and acid to the refrigerant every time I reset that breaker.

So once again we FIRST perform a full visual inspection of all the high voltage wires, terminals, contactor, capacitor, crankcase heater and the breaker itself. If that all looks OK then we pull the top and inspect the compressor leads and terminals themselves. Before you go pulling on the terminals or compressor plug make sure you are wearing gloves and safety glasses, it is possible for one of those terminals to blow out of the fusite at that moment and freeze your face or hands.

Another quick tip is take a photo of all wires and/or tag them before pulling them off. We all have cameras in our pockets nowadays which makes mis-wiring upon reassembly a thing of the past (I wish).

Now measure resistance to ground (In this case the copper stubs on the compressor) from each terminal. It is OK to use a megohmmeter if you want, just keep in mind that some compressors are still considered “good” by the manufacturer all the way down to 0.5 megaohms and some meters say “bad” at 20 megaohms.

Once you are certain as you can be that the compressor short to ground is the culprit or if it is reading between 0.5 and 20 megaohms to GROUND making you unsure I have one more task for you.

Now ISOLATE the compressor by taping and strapping up the plug or terminals so they aren’t touching anything. Now reassemble the unit and reset the breaker.

If it doesn’t trip and everything else (Condenser fan motor etc..)  runs properly then you can feel good about your diagnosis, if it trips again then it’s back to the drawing board.

Other Uses 

Isolation diagnosis can be used in things like finding system noises and even in finding open circuits by using jumper wires. Isolation diagnosis is taking a hypothesis and testing it with one component or conductor at a time allowing you to find the culprit through process of elimination.

On communicating systems where I wanted to be SURE it was the controller and not the wire I removed the controller from the wall and wired it directly to the fan coil board to make sure it still didn’t work even with no wire between. Sometimes my hypothesis was right and sometimes it was wrong but either way isolation diagnosis has saved me from looking dumb on many occasions.

— Bryan


P.S. – Bert Made this video a while back using isolation diagnosis to find a LV short

Service valves are so basic and we see them with such regularity that we can miss them altogether.

Before I give the tips I want to address the tech who tells the customer it was “probably the service valve” or “the caps were loose” as a plausible reason for a leak without actually doing a proper diagnosis. Don’t make excuses, find the leak.

Now some tips.

#1 – Look before you connect

Look for oil around ports BEFORE you connect your gauges every time. If you have a leaking schrader and cap you want to know that before you connect your gauges and eliminate that leak. Keep in mind that a service cap is NEVER meant to be the seal from a leak, it does act as an insurance policy against a tiny leak in a schrader. If you find a leaking schrader, replace it.

#2 – Be Gentle With the Heat 

No matter the valve make sure you protect it from heat when brazing or soldering (Here’s looking at you Staybrite #8 techs).

The schraders should be out when brazing anyway, but the internals of the valve are also sensitive to heat. Ever see a valve leaking from the stem? Odds are it was overheated at some point.

When opening and closing the valve DON’T CRANK DOWN so hard. We all know you are strong, but when you crank it open and closed like that you can over-compress and damage the seals and mating surfaces. Snug is good, if you need to “put your back into it” it’s probably too much.

#3 – Check Your Seals

A 1/4″ service port is actually just a 1/4″ flare fitting. Technically they don’t NEED a seal if the cap is a flare cap (think Trane brass caps). The only trouble with the brass flare caps is they do need to be on pretty snug to seal.

Most manufacturers have gone to caps with a rubber O-ring seal inside, they seal better and they only need to be finger tight. Before installing these caps get in the habit of checking the seal EVERY TIME. Make sure it’s there and that it’s in flat.

I have seen many leaks caused by an O-ring that got put in cockeyed and depressed the schrader slightly when the cap was installed.

#4 – Try the New Fangled Technology

We used to always advise using a bit of refrigerant oil when making flares and even when reinstalling the top caps on service valves. The oil doesn’t really “seal” anything but it helps you get a snug fit without twisting or damaging anything (the technical term is “galling”).

Trouble is, we are going away from mineral oil and toward POE and POE fouls if it is exposed to the air (humidity) for too long. Granted, a drop of mineral oil on a flare isn’t going to hurt a POE system but IT’S THE PRINCIPLE DANGIT!

I have raged against the use of thread sealants like leak lock in refrigerant circuits for years. I’ve seen teflon tape and leak lock on flare fittings and Chatleff fittings… Teflon tape and leak lock do not belong on refrigerant circuit components folks. They aren’t designed for that purpose and if they get in the system they are gonna cause issues. In many gases gumming up the threads and mating surfaces with these products can inhibit a good seal by getting between the flare mating surfaces.

A product I like is called Nylog it’s a very thick but constantly viscous product (never gets hard) and it won’t hurt the system if a little gets inside because it’s made of refrigerant oil.

You can put a drop on the threads and mating surfaces of all your flares, chatleff connections (the valve connections with the teflon seals), top caps on your service valves, pipe threaded ports…. everywhere.. but just a drop

You can also use it on your hose connections to get a better seal when pulling a vacuum.

Just use a small amount otherwise dirt will stick all over everything.

#5 – Using the Right Wrench and Back it Up 

For those systems that still use flare hex caps its best to use a 9/16 box end wrench or flare wrench (shown above) and use a backing wrench when removing the cap. All it takes is ONE TIME of breaking it off to regret using a big ‘ol adjustable wrench.

— Bryan


The following is based on a true story. No product was harmed in the making of this tech tip and some facts may have changed to protect the guilty and because I forgot some of them.

We got a job installing a new 1to1 split refrigeration case with R448a and it had a typical thermostatic expansion valve, headmaster and a suction stop.

We installed it using all the proper procedures we talk about all the time.

Purge with nitrogen, flow nitrogen while brazing, pressurize to the factory mandated low side test pressure, pull a deep vacuum to 250 microns and then do a decay test. Both sides pulled down nice and deep at the condensing unit and held.

Everything looked beautiful!

Until we started the unit up.

The head pressure was unusually high and the sight glass wasn’t clearing even though it showed subcooling.

A dead ringer for non-condensibles

After much consternation and handwringing we recovered the charge, re-evacuated and recharged with a virgin charge.


Before I give you the answer, see if you can look at the diagram at the top and figure out what happened.

It’s really not that complicated but it’s an easy sort of mistake to make.

When you pressurize a system with a non-bleed (hard shut off) expansion valve the valve will go fully shut when the evaporator / suction pressure goes high enough for the external or internal equalizer pressure to overcome the bulb pressure.

You may have noticed this when pressure testing a system where the high side pressure goes up and the suction goes up with it… then all of a sudden the suction stops rising. As you add more pressure to the high side it will keep going up but the suction pressure stays the same.

This happens because that valve has shut completely due to the external equalizer force overcoming the bulb pressure.

In this situation we forgot to force open the suction stop before we vented the nitrogen and performed the vacuum.

This left the pressurized nitrogen trapped between the slammed shut TXV and the suction stop.

Once the system was turned on the suction stop opened allowing the nitrogen to mix with the refrigerant causing the issue.

Preventable issue? Yes

And hopefully by reading this it will prevent you from making a similar mistake.

— Bryan

When mounting a TXV bulb or checking bulb placement there are a few important considerations (listed in order of importance)

  1. Mount the bulb on the suction line. Flapping in the breeze is no good.
  2. Mount TIGHTLY it with a proper metallic strap (usually copper, brass or stainless). Not zip ties, not tape.
  3. Position it on a flat, clean, smooth, portion of the horizontal suction line. Not on a coupling or an elbow.
  4. Mount it before the equalizer tube (closer to the evaporator than the EQ tube)
  5. When possible mount it at 8 or 4 o’clock on the suction line (or according to manufacturers specs) . This becomes more important the larger the suction line.
  6. When possible, insulate the bulb so that it is not influenced by ambient air temperature. It never hurts to insulate the bulb even inside the cabinet though not all manufacturers require it.
  7. If you do need to mount it vertically, make sure the tube points up not down

Poor bulb contact will (generally) result in a bulb that is warmer than desired, resulting in overfeeding and lower than desired superheat.

Finally… be gentle with the bulb and tube. They break easily.

You can read a more detailed description HERE

— Bryan

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