Heat Pump Flashcards
On a heat pump how can you tell which txv is in use?
In the cooling operation the indoor txv is used and during the heating operation the outside txv is in use
What happens to a heat pump when it’s in defrost mode?
1.)The outdoor fan gets turned off
2.) the reversing valve changes the flow of refrigerant
3.) the control board sends 24v through W to send power to electric heat strips
What 2 things triggers defrost mode in a heat pump?
1.)When the temperature outside is below 32degrees
2.) Timer
How does the accumulative timer work on a heat pump?
So there is 30 60 90 min run times. So for example if you set this to 60mins and your unit turned on and off for 20min three times at the end of that run cycle the board is going to check if the DFT is open or closed. If it’s closed it will initiate defrost
How does a DFT work?
It closes during temp decrease and opens when temp rises
If you see 80-50 degrees on a DFT, what does that mean?
So that means it’s going to close once the coil temperature hits below 30 degrees. And it’s not going to open back up until it reaches 80 degrees
Where does the Y terminal go through once it leaves the board?
It goes through both limit switches and the DFT and comes back to T1
Where does T1 go to?
How does the timer know how long the units running?
The side of the contactor.
As long as there is power to T1 it knows the units is running because it goes through both pressure switches.
On a heat pump you get three wires running from the fan motor
Black Yellow Brown
Where do those wires go?
Brown goes to the capacitor
Yellow goes to one of the two power legs on top of the contactor
Black goes into the relay on the board
What is a relay?
Switch
What are the two hookups for the relay coming from?
One is coming from the fan and the other is coming from the power leg on top of the contactor
Is the connections on the relay normally closed or normally open?
Normally closed
What causes the connections on a heat pump relay to open?
Defrost mode
Where does *O and *C lead to from the board?
Reversing valve
During defrost mode what’s going on with the electric and refrigerant?
So first your relay kills power to outdoor fan.
Next the reversing valve is going to put the system in ac mode,
So with the fan off not rejecting heat that discharge gas coming from the compressor is very hot and is now running through the coils and melts the ice.
While that happens the board sends 24v through *W back to handler and power on the sequencer or heat strips
How would you force a defrost on a heat pump?
On the board there are two test pins. While the unit is in heat mode you get a flathead and touch both the pins. Once you short the pins defrost happens
What does the compressor do in defrost mode?
It sends hot gas through the coils to melt all ice
If you have a heat pump coil that is a block of ice what do you check?
1.)make sure your outdoor fan works
2.) check the outdoor coil make sure it’s not dirty
3.)check the refrigerant, make sure it isn’t low, that way it heats properly and it’s able to defrost, if it doesn’t have enough refrigerant it won’t have enough hot gas to send to the coil during defrost
What’s the difference between single stage and two stage systems
Single stage operates like a light switch it’s either on or off no matter the temperature. Always using 100%
Two stage either blows 100% or 50% depending on temperature outside
