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HVAC Training: 6 Ways to Prevent Damage to Printed Control Boards or PCB’s

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How Static Electricity Kills Control Boards

Electrostatic Discharge is a Bigger Problem With Modern Electronics Than it’s Ever Been

When I first learned how to change a control board on a furnace, I was educated by my trainer to take great care in removing any static from myself before removing the board from the box.  He said I could damage the control board before the furnace even ran for the first time after the repair.  It’s called electrostatic discharge and it’s a bigger problem with modern electronics than it’s ever been.  This is what we’re going to talk about this week on Fox Family Heating and Air.

And for those of you who have experience handling control boards, let us know down below in the comments section if you have any other safety suggestions or any good war stories from your time in the field.  We’re always trying to learn as HVAC techs, and there’s no information better than the lessons you’ve learned and can pass on to us.

Reducing Electrostatic Discharge

About a third of all control board failures come from damage caused by electrostatic discharge.  You might have seen those pristine labs where they manufacture control boards.  One of the main goals for these rooms is to reduce static.  Once a control board is created, it’s prone to static damage.  If that damage were to happen at the lab the cost to manufacture another one is very little.  If the damage happens during testing it requires 10 times the cost to make it.  And if that board fails at the customer’s house, it takes 100 times the cost to manufacture a new board at the lab, package it, ship it to an HVAC warehouse, ship to the HVAC contractor, who drives it to the customer’s house, and has it ready for the customer to replace it, and put a warranty on it.

When it comes to static damage to a control board, it’s not so much about the voltage being transferred from you to the metallic parts of the board itself, but the resistance it incurs as it travels through pins, transistors, and other parts of the board along its path to ground.

The Shrink-Down

You’ve seen those big controls and relays that were used on decades-old furnaces.  They’re the same controls used today to direct the sequence of events that start the furnace and shut it down.  Anyone who has worked on an old furnace can tell you those relays and switches take up a lot of space in the control panel.   These days all those relays, transistors and switches have been shrunk down to the point that they now fit on a printed control board the size of a small napkin. 

Those old relays and other controls being larger than today’s parts were constructed with heavier materials.  That’s why they’re more durable over time.  The strength of the materials used to build small control boards is obviously not going to be as durable as those bigger, heavier parts.  You know the saying; “they don’t make them like they used to?”  Well, there’s something to that.

The Victim

A static discharge 20 years ago would have been harmless to those controls.  Today that same discharge through the board can result in catastrophic damage.   Transistors are often the victims of static shock to a control board.  But pins, brittle solder, and the silicon itself can all be deformed by the heat that travels through during a static discharge.

Damage like this can make a control for the blower motor, which is supposed to be off at a given time, to a blower that s always on now.  Or a safety switch that is normally closed to become constantly open.  These parts of the furnace that are needed to work in a certain order can be thrown out of whack very quickly with the slightest arc from your body to the control board.

Unseen Damage

Most people don’t even know they’re charged with static electricity as they cross the carpet floors and on to the HVAC system of a customer’s house until they feel the spark travel from their fingers to the brand-new control board they’re changing out.  Some of those techs also don’t know they’ve just damaged that expensive control board their customer is getting ready to pay for either.

You don’t have to be wearing a flannel shirt and your favorite pair of wooly socks to develop static.  Although clothing like that, as well as other situations, can create a significantly higher amount of energy than the body can store, which will need to be discharged at the next available piece of metal you touch.

Why Inspect?

Suppose you were out on a preventive maintenance or a service call doing a visual check of the backside of a control board.  We all know of the solder connections on the back of those boards which are receptors for a Molex plug that controls many of the basic functions of the furnace.  The heat from even a minuscule 24 volts, over time, will fracture those solder connections, which is why we inspect the back of the boards on a regular basis.  But if we bring with us a body full of static, and touch that control board, we can create a very minor defect in the board, or make a pre-existing, undetected condition even worse.  All of these fractures break down the control board over time until it completely fails.

Every control board I’ve changed was stored in an anti-static bag that comes inside a cardboard box.  Even those anti-static bags are conductive!  But they do help reduce and negate any static electricity the board might encounter during shipping and riding around in the back of your truck.

What Can We Do?

So, what can we do to prevent ourselves from damaging printed circuit boards in the future?

1. Ground Yourself

Do what my trainer told me to do.  Ground yourself to the furnace before touching the delicate components inside them.  Something that has a direct path to earth.  When we ground ourselves, we’re removing any excess voltage we may have created and carried with ourselves as we walked to the furnace.

2. Avoid Carpet and Rugs

Try working in an area where you’re not standing on carpet or area rugs.  These will encourage you to generate static even after you’ve already grounded yourself to the unit the first time!  A canvas drop cloth is less likely to generate that same static.  Working on bare or concrete floors is even more ideal.

3. Humidity Levels

I know you can’t change this while you’re servicing the HVAC system, but understanding the humidity levels in the room can help.  A room that has 40% to 50% humidity is less likely than a dryer room to encourage static.

4. Remove Voltage Potential

Make sure you’ve unplugged the furnace.  You want to make sure there are no electrical currents running through the system.

5. Handle with Care

When you do take the control board out of the anti-static bag, or when you remove one from the furnace to inspect it, make sure you are only touching the sides of the board.  Voltage potential is conducted through all the metallic parts of the board.  These are the areas you don’t want to have your fingers all over.

6. Stay Hydrated

Speaking of hands, keeping your skin moisturized by drinking plenty of water and even using lotion will help keep static-electricity down.  Dry skin encourages static to build up even after you’ve grounded yourself a first time.  You’re not off the hook as far as static discharge goes. Grounding yourself to the furnace multiple times is not unheard of.

Here’s a Little Tip!

Want to reduce the chance of that painful snap between you and the metallic object you choose to ground yourself to?  Use something like your metallic car keys to touch that ground.  This allows the discharge to travel straight through the key instead of going straight to your hand.


I hope this helps you with your question as to ESD damage to control board furnaces.  If you’ll take the time to ground yourself properly, you’ll reduce the chance of transferring the voltage to the control board.

Thanks for stopping by and we’ll see you on the next blog post!

Fox Family Heating & Air serves Sacramento, Rancho Cordova, and all of Northern California. If you’re looking to schedule HVAC service in these areas, give us a call!

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