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HVAC and Plumbing Distributor
Steven Simmons

Steven Simmons

Technical Services Manager
Southwest District

Schematic Reading Basics

For those new to the field, do you find it intimidating when you have to rely on the wiring schematic on a unit to figure out what a device is or what it should do? Or do you sometimes get confused looking at all the endless lines, weird symbols, and acronyms?

         I’ll be first in line to tell you I shared those same feelings when I started my HVAC career. I am going to share some basics to reading Residential Wiring schematics with you in the article. The cool thing is almost all symbols are the same across all brands, and TYPICALLY the details within the symbols have a meaning, but every now and again the symbol will be generic and you will have to add in context clues to determine what they are.

 

Let’s dive right in… Typical Residential Carrier wirings diagrams resemble this:

schematic
Drawings in this article are from two Carrier manuals:25HNB9---2W & 50VR---07SI

The Connection Diagram is best used when you need to know exactly where the high voltage wires are terminated, the Ladder form is best when trying to figure out how power flows from L1 to L2 through the devices- I have added two arrows to indicate L1 & L2.

Legend–ANYTIME you have an acronym (which is where a word or group of words are shortened into just a few letters) the full meaning can always be found here.

Notes– Periodically you will see “see note x” on a diagram, refer to this area for details pertaining to the area dictating the note.

Symbols

Okay, now let’s break down some common symbols:

equipment ground symbol

This symbol is for an equipment ground- almost any time you see three lines parallel either horizontally or vertically- they will mean earth/ ground.

Here is an Outdoor Fan Motor where you can see it contains two windings, Start and Run. Also, in green is another symbol for ground

defrost thermostat symbol

This is a DeFrost Thermostat. This zig-zag line means temperature. TYPICALLY, if you look at the right bubble on limits: if the line lands on top then it means “close on drop and open on rise” and if it’s on the bottom then it would mean “close on rise and open on drop” Remember this!

crankcase heater

This is a CrankCase Heater- According to the description above: it will open on temperature rise.

Let’s add more to this same rule

Without looking up the acronyms I want to break these down.

Anytime you see these half circles they mean pressure. With this known, we can now see that the top switch will “open on pressure rise”- this is a High-Pressure Switch and the bottom will “open on pressure drop”- it is a Low-Pressure Switch.

Lastly, if you see a backwards “C” next to a straight line like is presented here, then it is a capacitor. Some drawings will rotate this symbol so it will then look like a “U” and a flat line. This particular one is a Start Capacitor.

 

Now, keep this basic knowledge memorized and build onto it. Take a look at the close-up diagrams below and look for the symbols we just discussed and see how they interact with the electrical system.

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Alabama Locations

Anniston (256) 241-3026 105 E D St, Anniston, AL 36201
Auburn (334) 734-8011 2295 1st Ave, Opelika, AL 36801
Birmingham (205) 250-7714 516 31st St N, Birmingham, AL 35203
Dothan (334) 836-1035 205 Wedgewood Dr, Dothan, AL 36303
Gulf Shores (251) 968-2660 820 Commerce Dr, Gulf Shores, AL 36542
Huntsville (256) 859-2691 391 Nick Fitcheard Rd NW, Huntsville, AL 35806
Loxley (251) 964-2707 30020 Co Rd 49, Loxley, AL 36551
Mobile (251) 476-2220 5522 W Commerce Blvd West, Mobile, AL 36619
Montgomery (334) 262-4855 861 Plantation Way, Montgomery, AL 36117
Muscle Shoals (256) 383-6904 107 Commerce St, Muscle Shoals, AL 35661

Georgia Locations

Albany(229) 432-5254205 Baldwin Dr, Albany, GA 31707
Athens(706) 548-2563105 Whitetail Way, Bogart, GA 30622
Atlanta(404) 875-77551290 Tacoma Dr NW, Atlanta, GA 30318
Augusta(706) 651-19503618 Wrightsboro Rd, Augusta, GA 30909
Brunswick(912) 265-5193275 Rose Dr, Brunswick, GA 31520
Columbus(706) 322-38706201 W Hamilton Park Rd, Columbus, GA 31909
Conyers(770) 918-9132335 Gees Mill Business Pkwy NE, Conyers, GA 30013
Forest Park(404) 361-24745158-C Kennedy Rd, Forest Park, GA 30297
Gainesville(770) 297-93352472 Hilton Dr, Gainesville, GA 30501
Lawrenceville(678) 442-10602111 Cedars Rd SE, Lawrenceville, GA 30043
Lithia Springs(770) 948-3451320 Thornton Rd #106, Lithia Springs, GA 30122
Macon(478) 474-85445527 Thomaston Rd, Macon, GA 31220
Marietta(770) 426-05511060 Triad Ct, Marietta, GA 30062
Newnan(770) 239-210570 Enterprise Ct, Newnan, GA 30265
Peachtree Corners(770) 239-21006675 Jones Mill Ct, Peachtree Corners, GA 30092
Savannah(912) 232-1228103 Central Jct Blvd, Savannah, GA 31405
Statesboro(912) 764-8841126 W Parrish St, Statesboro, GA 30458
Valdosta(229) 245-8200363 Connell Rd, Valdosta, GA 31602
Warner Robins(478) 953-3727110 Byrd Way, Warner Robins, GA 31088

South Carolina Locations

Hilton Head(843) 689-34043715, 21 Hunter Rd, Hilton Head Island, SC 29926

Florida Locations

Fort Walton Beach(850) 244-201776 Beal Pkwy SW, Fort Walton Beach, FL 32548
Panama City(850) 913-05853012 Lisenby Ave, Panama City, FL 32405
Pensacola(850) 438-10054405 N. Palafox Street, Pensacola FL 32505

Mississippi Locations

Hattiesburg(601) 579-96701851 Lincoln Rd, Hattiesburg, MS 39402
Ocean Springs(228) 497-5090Sunplex Industrial Park, 5717 Suntec Drive, Ocean Springs, MS 39564

Commercial Sales

Norcross – North Georgia Hub
(800) 282-4911

Birmingham – North Alabama Hub
(205) 250-7714

Macon – Southwest Hub
(800) 342-9250

Loxley – Gulf Coast Hub
(800) 239-7419

Savannah – Southeast Hub
(800) 822-7617

Commercial Parts

 CompanyWeb AddressDescription
Airzonewww.airzoneinc.comCustom and Underfloor Air Handlers
Aladdin Metal Productswww.aladdinmetalproducts.comCurb Adapters and Roof Curbs
Aprilairewww.aprilaire.comIndoor Air Quality Products
Autaniwww.autani.comBuilding Automation and Controls
Bardwww.bardhvac.comHeat Pumps,Gas/Electric, and Wall Mounted Air Conditioners
Bryantwww.bryant.comCommercial, Industrial, Residential Heating & A/C Products and Controls
Carrierwww.commercial.carrier.comCommercial and Residential Heating & A/C Products
Data Airewww.dataaire.comPrecision Air Control for Data Processing Centers
 DXairwww.dxair.comPool dehumidification systems
 First Companywww.firstco.comFan Coil Units
Global Plasma Solutionswww.gpshvac.comAir Purification and Bi-Polar Ionization
 Greewww.greeusa.comPTACs
 Hayes Fluid Controlswww.haysfluidcontrols.comHose Kits and Control Valves
 iAirewww.myiaire.comCommercial Air Purification using ionization with energy savings
 IslandAirewww.islandaire.comPTACs, Vertical Units, Water Source Heat Pumps
 i-Vuwww.commercial.carrier.comBuilding Automation and Controls
 Magic Airewww.magicaire.comFan Coil Units
 Micro Metlwww.micrometl.comRoof Curbs, RTU Accessories, & ERVs
 Modinewww.modine.comGas-Fired Unit Heaters, Duct, Furnaces, Hot Water Cabinet Unit Heaters, Makeup Air, and Dedicated Outdoor Air Systems
 Network Thermostatwww.networkthermostat.comInternet Thermostats, Wifi Themostats, Ethernet Thermostats
Paynewww.payne.comResidential Heating & A/C Products
Rawal Deviceswww.rawal.comContinuous Capacity Modulation and Dehumidification for DX Systems
Renew Airewww.renewaire.comFixed-Plate ERVs
Totalinewww.totaline.comCompressors, Parts, and Supplies
United CoolAirwww.unitedcoolair.comModular All-Indoor HVAC Systems
 Warren Technologywww.warrenhvac.comElectric Heaters
 Wilo Pumpswww.wilo-usa.comPump Systems for HVAC and Water Supply and Sewage