Honeywell T87 Round Thermostat: Home Heating Control

Honeywell’s old thermostat models, such as the Honeywell T87 which prominently features a round design, represent a significant era in home heating control. The bi-metallic strip inside these thermostats are a temperature-sensitive component. The strip will bend in response to temperature changes, which then causes the thermostat to adjust the heating or cooling system, to maintain a consistent indoor climate, despite it lacks the advanced programmability of modern smart thermostats.

Let’s take a trip down memory lane, shall we? Imagine a world where smart homes were the stuff of science fiction, and the humble thermostat reigned supreme. In that world, Honeywell was – and still is – the undisputed champion! For generations, Honeywell has been synonymous with reliable and innovative thermostat technology. They’ve been keeping our homes cozy in the winter and cool in the summer.

Now, let’s talk about icons. Picture this: a simple, elegant circle mounted on the wall – the Honeywell Round Thermostat (T87). This isn’t just a thermostat; it’s a design classic, a symbol of mid-century modernism, and a testament to simple, effective engineering. Other classic models, equally robust and dependable, have graced our homes over the years, quietly and efficiently doing their job.

You might be asking, “Why should I care about these old relics?” Well, the answer is threefold: reliability, savings, and history. These thermostats were built to last, often outperforming their modern, tech-heavy counterparts. Plus, understanding how they work can save you money on repairs and replacements. And let’s not forget the sheer satisfaction of preserving a piece of history!

There’s a certain nostalgia associated with these classic thermostats. They remind us of simpler times. But it’s not just about sentimentality. It’s about appreciating the craftsmanship and simplicity of a device that has stood the test of time. So, whether you’re a vintage enthusiast, a practical homeowner, or just curious about how things work, you’re in the right place. Let’s dive in and uncover the secrets of these enduring Honeywell classics!

Inside the Classics: Key Components Explained

Alright, let’s crack open these vintage Honeywell thermostats and see what makes them tick! These aren’t your fancy-pants, internet-connected smart thermostats; we’re talking about real mechanical ingenuity. Understanding these core components is key to appreciating (and maybe even repairing) these trusty relics.

Bimetallic Strip: The Temperature Whisperer

Think of the bimetallic strip as the thermostat’s sixth sense. It’s made of two different metals bonded together, each expanding at a different rate when heated. This difference in expansion causes the strip to bend. The strip acts like a tiny, low-tech thermometer.

As the room temperature changes, the strip curls and uncurls. This precise movement is the brain of the operation. It’s directly linked to the switch that tells your HVAC system to kick on or chill out, keeping your home cozy or cool.

Mercury Switch: Completing the Circuit (Carefully!)

Now, here’s where things get a little old-school – and potentially hazardous. The mercury switch is a sealed glass bulb containing a small amount of liquid mercury. As the bimetallic strip bends, it tilts the mercury switch. This causes the mercury to flow and either complete or break an electrical circuit. Completing the circuit is like flipping a light switch that signals to your heating or cooling system to turn on.

SAFETY WARNING: This is SUPER important. Mercury is a dangerous neurotoxin. If you’re dealing with a thermostat that has a mercury switch, treat it with the utmost care. Do not break the glass! If you’re replacing the thermostat, responsible disposal is non-negotiable. Many local recycling programs or hazardous waste disposal sites will accept mercury-containing devices. Check your local regulations and resources for proper disposal. Never throw a mercury thermostat in the trash!

Heat Anticipator: Fine-Tuning the Toasty

The heat anticipator is a clever little device that prevents your furnace from overshooting the set temperature. It works by adding a small amount of heat to the bimetallic strip while the furnace is running. This tricks the thermostat into thinking the room is warmer than it actually is and shuts off the furnace slightly before the set point is reached.

The purpose of this is reducing temperature fluctuations and improving heating efficiency by reducing unnecessary cycling. Less cycling can lead to a longer lifespan for your heating system and a more consistent temperature in your home. A win-win!

Wiring Terminals: Connecting to Your HVAC System

The wiring terminals are the points where the thermostat connects to the nervous system of your HVAC system. These terminals link the thermostat to the control wires that tell your furnace, air conditioner, or heat pump what to do.

Proper connections are vital for the thermostat to work correctly. Loose or incorrect wiring can lead to all sorts of problems, from the system not turning on at all to it running constantly. Make sure these connections are secure, clean, and correctly matched to your HVAC system.

Cover Plate/Housing: Protection and Aesthetics

Finally, we have the cover plate or housing. This is what you actually see and touch. Its primary purpose is to protect the internal components from dust, damage, and curious fingers.

But let’s be real – it also plays a huge role in the thermostat’s aesthetics. The iconic Round Thermostat (T87) cover is instantly recognizable, and many other styles exist to match different home decors. It’s the face of your heating and cooling control, adding a touch of vintage charm to your wall.

Deciphering the Features: Understanding Functionality

Alright, so you’ve got this cool, old-school Honeywell thermostat on your wall, and you’re probably wondering, “What do all these little switches and dials actually do?” Fear not, intrepid homeowner! We’re about to decode the secrets behind those classic controls and unlock the full potential of your trusty thermostat. Think of it as learning the ancient language of climate control. Get ready to control your climate!

Thermometer: Accurate Temperature Readings

First up, the thermometer. Seems obvious, right? It tells you the temperature! But accurate temperature readings are the cornerstone of effective climate control. If your thermostat thinks it’s 80 degrees when it’s really 70, your AC is going to be working overtime (and your wallet will be crying).

Factors that can mess with accuracy? Placement is key. Is your thermostat baking in direct sunlight or huddled near a drafty window? That’s no good! Also, these old thermometers can drift over time. So, if you suspect yours is off, it might be time for a little recalibration.

Set Point Dial/Lever: Setting Your Desired Temperature

Next, we have the all-important set point dial or lever. This is where you tell your thermostat what temperature you want it to be. Turn the dial, slide the lever, and voila! You’re setting the stage for climate perfection (or at least, climate adequacy).

The mechanics are pretty simple: when the room temperature dips below (in heating mode) or rises above (in cooling mode) the set point, the thermostat kicks on your HVAC system. Think of it as a tiny, temperature-sensitive overlord, commanding your furnace or AC to do its bidding. It’s a direct influence!

System Switch: Selecting Heating, Cooling, or Auto

Now, let’s talk modes. The system switch is your master control for choosing between heating, cooling, or the ever-mysterious “auto” mode.

• Heating: This tells the thermostat to only activate the furnace when the temperature drops below your set point.
• Cooling: The opposite of heating, it engages your AC unit when things get too toasty.
• Auto: This is where the thermostat decides for itself! It’ll switch between heating and cooling as needed to maintain your desired temperature. Great for those unpredictable spring and fall days, where you might need heat in the morning and AC in the afternoon.

Fan Switch: Controlling Air Circulation

Don’t underestimate the power of the fan switch! This little switch controls whether your HVAC fan runs continuously or only when the system is actively heating or cooling.

• Continuous: Keeps the air circulating, which can help even out temperatures throughout your home and improve air quality.
• Auto: The fan only runs when the furnace or AC is on, which can save energy.

Which mode is right for you? It depends on your priorities! Better circulation or lower energy bills? The choice is yours!

Leveling Bubble/Indicator: Ensuring Accurate Readings

Finally, we have the often-overlooked leveling bubble or indicator. This tiny feature ensures that your thermostat is perfectly level, which is surprisingly important for accurate temperature readings.

If your thermostat is crooked, gravity can interfere with the internal mechanisms, leading to inaccurate readings and inconsistent temperatures. Keep an eye on that bubble and make sure it’s centered. A little adjustment can make a big difference in your comfort! Leveling is your friend!

Troubleshooting Common Issues: Restoring Functionality

Okay, so your trusty old Honeywell isn’t quite keeping things cozy (or cool)? Don’t sweat it! These old thermostats are built tough, but like any mechanical device, they can sometimes get a little cranky. The good news is that a little TLC can often bring them back to life. Let’s dive into some common issues and how to tackle them!

Dust/Debris: Cleaning for Optimal Performance

Think of your thermostat as the wise old owl of your HVAC system – it’s always watching the temperature! But just like any wise owl’s perch, dust and debris can accumulate over time. This gunk can insulate the bimetallic strip, throwing off its temperature readings and causing your thermostat to act a little… off.

• The Culprit: Airborne dust, pet dander, cobwebs (yes, even in thermostats!), and general household grime.
• The Symptoms: Inaccurate temperature readings, delayed response times, or the system not turning on/off when it should.

• The Cure:

  1. Power Down: Always turn off the power to the thermostat at the breaker box before you start poking around. Safety first!
  2. Gentle Removal: Carefully remove the thermostat cover. Most covers simply pull off or are held by a few screws.
  3. Dust Be Gone: Use a soft brush (like a clean toothbrush) or a can of compressed air to gently remove dust and debris from all visible components, including the bimetallic strip, contacts, and inside the cover.
  4. Surface Wipe (Optional): If there’s stubborn grime on the cover, you can lightly dampen a soft cloth with water (make sure it’s not dripping wet!) and wipe it down.
  5. Reassemble: Once everything is clean and dry, carefully reassemble the thermostat.

Loose Wiring: Identifying and Securing Connections

Imagine your thermostat’s wires as tiny roads delivering important messages to your HVAC system. If those roads are bumpy or disconnected (loose wiring!), the message gets garbled, and your system might not respond correctly.

• The Culprit: Vibrations, age, or simply a wire that wasn’t tightened properly in the first place.
• The Symptoms: Intermittent operation, the system not turning on/off at all, or the thermostat seemingly having a mind of its own.

• The Cure:

  1. Power Down (Again!): You know the drill – flip that breaker!
  2. Careful Inspection: Gently tug on each wire connected to the terminals. If any feel loose, that’s your culprit.
  3. Tightening Time: Use a small screwdriver to carefully tighten the screw on the terminal where the loose wire is connected. Make sure the wire is securely held in place, but don’t overtighten – you could strip the screw.
  4. Check for Corrosion: While you’re at it, inspect the wires and terminals for any signs of corrosion.
  5. Reassemble and Test: Put the thermostat back together and restore power. Test to see if the problem is resolved.

Electrical Safety: Always double-check that the power is off before touching any wires. Use insulated tools whenever possible and be extra careful!

Calibration Problems: Adjusting for Accuracy

Sometimes, even a clean and well-connected thermostat can start to display inaccurate temperature readings. This is often due to drift or component aging – basically, the thermostat’s internal “sense of temperature” gets a little wonky.

• The Culprit: Age, environmental factors, or subtle changes in the thermostat’s internal components.
• The Symptoms: The thermostat displaying a temperature that doesn’t match the actual room temperature, leading to over- or under-heating/cooling.

• The Cure:

  1. Locate the Calibration Screw: Many older Honeywell thermostats have a small calibration screw, usually located on the front or back of the thermostat.
  2. Compare and Adjust: Use a reliable thermometer to determine the actual room temperature. Compare this to the temperature displayed on the thermostat.
  3. Fine-Tune: Use a small screwdriver to gently turn the calibration screw until the thermostat displays the correct temperature. Make small adjustments and allow the thermostat some time to stabilize between adjustments.

Dirty Contacts: Cleaning Corroded Connections

The contacts inside your thermostat are like tiny switches that complete the electrical circuit, telling your HVAC system to turn on or off. If these contacts become corroded or dirty, they can’t make a good connection, leading to all sorts of problems.

• The Culprit: Oxidation, humidity, and general exposure to air can cause corrosion on the contacts.
• The Symptoms: Intermittent operation, the system not turning on/off reliably, or a “clicking” sound from the thermostat without the system responding.

• The Cure:

  1. Power Down (You Know the Song!): Safety first, always!
  2. Expose the Contacts: Carefully remove the thermostat cover and locate the contacts (usually small metal points or blades).
  3. Gentle Cleaning: Use a special contact cleaner for electronics on a cotton swab to gently clean the contacts. You can also use a very fine grit sandpaper (like 600 grit or higher) to lightly polish the contacts, but be extremely careful not to damage them.
  4. Clean the Contacts: After cleaning, use a clean cotton swab to dry the contacts.
  5. Reassemble and Test: Put the thermostat back together and restore power. See if that fixes it!

Prevention: To minimize future corrosion, try to keep the area around the thermostat clean and dry.

Connecting to HVAC Systems: Understanding the Interface

Alright, so you’ve got this awesome old Honeywell thermostat, and you’re wondering how it actually talks to your furnace, AC, or heat pump, right? It’s not magic, although sometimes it feels like it when you get that perfect temperature just right. Let’s pull back the curtain and see how these old-school thermostats orchestrate the climate control in your humble abode.

Furnace: Controlling the Heating Cycle

Think of your thermostat as the brains of the operation, and your furnace as the brawn. When the temperature dips below your set point, the thermostat sends a signal to the furnace. This signal tells the furnace, “Hey, time to fire up and get this place warm!”. The thermostat essentially closes a circuit, which tells the furnace to ignite the burners and start blowing that sweet, sweet heat. When the room reaches the set temperature, the thermostat breaks the circuit, and the furnace shuts down until needed again. It’s a simple on/off switch, but crucial for those cozy winter nights.

Air Conditioner/AC Unit: Managing the Cooling Cycle

Summer rolls around, and suddenly cozy isn’t the vibe anymore. The process is pretty similar to heating, but in reverse. When your room gets too toasty, the thermostat sends a signal to your air conditioner, saying, “Cool it down, buttercup!”. This signal activates the AC unit’s compressor and fan, which then extracts heat from your home and blows out cold air. Again, once the thermostat senses the desired temperature, it cuts the signal, and the AC takes a break. It’s a constant dance, keeping you comfortable no matter what the weather throws your way.

Heat Pump: Dual-Function Control

Now, heat pumps are a bit like the chameleons of HVAC systems. They can both heat and cool, which means the thermostat has to be a bit more versatile. In heating mode, the heat pump extracts heat from the outside air (yes, even cold air contains some heat!) and pumps it inside. In cooling mode, it reverses the process, removing heat from your home and dumping it outside. The thermostat controls this reversing valve, telling the heat pump whether to heat or cool based on your settings. So, even though it might seem like it’s breathing fire one minute and blowing ice the next, the thermostat is just following your orders.

HVAC Wiring: A Closer Look at Connections

Okay, let’s talk wires. Now, we’re not going to turn you into an electrician overnight, but understanding the basics can save you some headaches. Low-voltage wiring is the name of the game here, typically 24 volts. You’ll usually see a few common wires:

• Red (R): Power wire, usually 24VAC
• White (W): Heating wire
• Yellow (Y): Cooling wire
• Green (G): Fan wire

Now, remember that wiring color codes can vary, especially in older systems. Always double-check your specific setup and, if you are uncertain, consulting a professional is always your best bet. Common wiring issues include loose connections, incorrect wiring (maybe someone got a little too creative in the past), or shorts. If you’re having problems, start by ensuring all the wires are securely connected to the correct terminals. And, for the love of all that is safe, turn off the power before you start poking around with wires!

Safety First: Essential Precautions – Because Zapping Yourself is Not a Feature

Okay, folks, let’s talk safety. We all love saving money and keeping these vintage thermostats humming, but let’s be real: electricity and toxic materials aren’t exactly a match made in heaven. So, before you even think about unscrewing that cover plate, let’s drill down on some crucial safety measures. Trust me; a little precaution goes a long way in avoiding a shocking experience (pun intended… kinda).

Electrical Safety: Don’t Become Part of the Circuit

We’re dealing with low-voltage circuits, which is less scary than the high-voltage stuff, but still packs enough punch to ruin your day. The absolute, number one rule? Turn off the power! Head to your breaker box and flip the switch controlling the thermostat circuit to the “off” position. Think of it as hitting the pause button on potential electrocution.

Once you’ve killed the power, here’s what else to keep in mind:

• Insulated Tools Are Your Friends: Use tools with rubberized handles. It’s like wearing oven mitts for electricity—a comforting barrier.
• Avoid Touching Bare Wires: Seriously, it’s a no-brainer. Even with the power off, treat those wires with respect.
• Test It to Be Sure: Use a non-contact voltage tester to confirm the power is off. Never assume.

Think of this as your electricity safety mantra. Repeat it three times before proceeding.

Mercury Disposal: Handle with Extreme Care

Now for the potentially icky part: mercury. Many older Honeywell thermostats use a mercury switch, which is a sealed glass vial containing a tiny ball of liquid mercury. Mercury is toxic, and you do not want to break that vial. If you suspect your thermostat contains mercury, handle it with extreme care.

If the vial breaks:

• Do NOT Vacuum: This will spread the mercury vapor.
• Ventilate the Area: Open windows and doors to air out the room.
• Use Rubber Gloves: Protect your skin from direct contact.
• Carefully Collect the Mercury: Use an eyedropper or small pieces of stiff paper to gather the mercury beads. Place them in a sealed container.
• Clean the Area Thoroughly: Use a damp cloth to wipe up any remaining residue. Dispose of the cloth properly.

But better than the clean-up process, is to not break the vial.

Disposal is Key:

• Find a Hazardous Waste Facility: Do not throw the thermostat in the trash! Contact your local waste management authority to find a hazardous waste collection site.
• Check with Recycling Programs: Some municipalities have programs for recycling mercury-containing devices.

Here are some helpful resources for finding local disposal sites:

• Your Local Waste Management Website: A quick Google search for “[Your City/County] Waste Management” should point you in the right direction.
• Earth911: This website (Earth911.com) allows you to search for recycling centers near you.
• Call2Recycle: Another great resource for finding battery and electronics recycling locations (Call2Recycle.org).

Seriously, folks, mercury is nasty stuff. Dispose of it properly. Your planet (and your nervous system) will thank you.

So, whether you’re a vintage enthusiast or just trying to keep your home cozy, those old Honeywell thermostats have a certain charm. They might not have all the bells and whistles of the new models, but they get the job done with a classic, reliable style. Happy tinkering!