Understanding HVAC Wiring Diagrams: Key Symbols Explained

all right we're back at our split split uh system heat pump wiring diagram and schematic another thing you need to know

about wiring diagrams and schematics is what all of the symbols mean so you have all the wiring and all of these symbols

and we're going to go through the through them one by one these are common hfac schematic

symbols the manufacturers are going to use these symbols on all the wiring diagram

where the Legends may be different and the and the um labeling may be different these schematic symbols will always be

the same the first one is wires connected that's depicted by a DOT connecting the wires which are depicted

by these black lines so whenever you see a black line Crossing another black line with a DOT it's connected um sometimes

it'll be a circle but not um and not a black dot second symbol is wires not

connected this is the most common schematic symbol you'll see for wires that are not connected it's less

common to see this this is easier to depict but you're going to see that the wires are crossed but without that black

dot don't get confused those wires are not connected the next one is the contact

symbol this is going to be for a relay or compressor contactor or motor prot contactor now the no stands for normally

open and the NC stands for normally closed this will when you see a normally open contact that's the condition that

it's in with no power supplied whatsoever with a c with your um your HVAC system at rest and not

operating the normally closed is the same thing that's a closed contact with no power connected to the contactor or

to the relay the one thing you have to remember and this gets confusing when you're

troubleshooting if the relay or contactor is energized the normally open contact will close and the normally

closed contact will open we'll cover um contactors and relays in more detail in a later

screencast here's one that's unique to to HVAC and that's the pressure controls symbols this is there are two of them

and these the first one depicts a open on temperature rise and as you can see if

the temperature increases it's going to push the contact open and open up the contact this is close on temperature

rise which means as the pressure if the pressure is high enough it's going to have the contact be closed if the

pressure decreases it's going to pull that contact down and open it up gets a little bit confusing because it's always

talking about um open on pressure rise and close on pressure rise but just remember that if the pressure

decreases it's going to pull this open this especially the one that's closed on temperature rise again we'll cover these

pressure controls in a little bit more detail on a later screencast the next one are thermostat

controlled switches and contacts this is exactly the same as the U pressure controlled

this one this symbol right here this little zigzag depicts a temperature activated

switch and this one here will open on temperature rise and this one closes on temperature

rise and the final one we'll look at today is a capacitor and that's this um this symbol right here and we'll take a

look at where all of these um come together on the schematic diagram for the um nordine heat pump so let's take a

look so the first one here is here are our wires and you can see that um black dot

indicates that those wires are connected now if you look over here you don't see that black dot so these wires just

cross over each other and are not connected that's the first one that we took a look

at okay let's take a look here at uh contacts here's a contact right here this is normally there here's two

normally open contacts from a contactor and here is a normally closed contact on a contactor again these are in the

there's there are there is no power supplied to the contactors and the system is at rest so it's not operating

it does doesn't have any switches operating closing or opening all right here's another one uh

um this is our defrost termination and this is a temperature operated switch and can you

figure out which one this is this is an this is an open on temperature rise switch and here's

another one right here that's an outdoor temperature sensor as well so both of these as the temperature goes up will

open now we don't have any um pressure switches in this schematic diag

but they're going to be somewhere in the circuit and you'll be able to determine which one is which

the other thing you can do is print out that little diagram that we had at the on this one right here and keep that in

your pocket or in your notebook just to help you remember until you get familiar all right the last one here is

the capacitor and there it's pretty simple it's it is uh indicated by dual capacitor but there you see that

schematic symbol right there so we'll delve into more of these later and uh explain the pressure and

temperature contact symbols in more detail on a later screencast