Hvac Revamped Flashcards
What is the purpose of a receiver tank?
It stores sub cooled liquid
The sight glass is upstream of (right before) the…..,
Metering device
The king valve is on the outlet of the…
Receiver
Which of these refrigerants is NOT used in refrigerators and freezers?
R-22
R-410A
R-404A
R-134A
R-410A
On a automatic pump-down refrigeration system, which component opens the electrical circuit to the compressor to turn off?
The Low pressure switch
Which can cause the evaporator to freeze up on a reach in commercial refrigerator?
Blocking the airflow with too much product
If a system with a new filter drier has been running for 15 minutes, seeing bubbles in the liquid line sight glass means there is…..,.,,
No subcooling
If the defrost cycle does not intimate on a freezer,the (blank) will continue to attract humidity to it and completely freeze over
Evaporator
If a fuse blows what does that mean?
fuse blows anytime one of your energized circuits make contact with common or ground without first going through a load first
What are three ways to check for a blown fuse?
1.loose wire nut connection
2. One of the wires loose from the terminal
3.one of the wires cut or damaged
With your volt meter how do you test for a blown fuse?
you would want to check continuity or you can check with ohms. If you have a OL reading it’s bad but if you get some type of resistance your fine
If you have a OL reading while checking for ohms on a fuse what does that mean?
You should get some type of reading. If you get a OL reading, you have a bad fuse. Not passing electrical current
Say your indoor blower motor not turning on. And you check from *G to *C and it’s getting 24v where would you check next?
Then with your probes you would want to check from your neutral wire to your fan speed wire on the circuit board. If you get nothing bad board
In defrost mode on a heat pump it’s basically running in normal ac mode at the condenser besides what?
The condensing fan is shut off not rejecting heat causing the outside coil to heat up faster
During defrost mode what is the .W terminal at the condenser doing?
Because you don’t want your heat to drop while it’s defrosting the outside coil it’s going to power 24v back at the control board and turn on your furnace or electrical heat
What two things trigger the heat pump from out of defrost mode?
Until a time commitment is met at 10min (or whatever it’s set too) or temperature sensor is satisfied
What three reasons will cause the evaporator coil to freeze?
- Low indoor airflow
2.low refrigerant charge
3.liquid line restriction
Sometimes technicians will try to raise the low side temperatures by charging the unit up instead of fixing the issue. How would you indicate this?
Very clear indication of this is very high subcooling anywhere from 21 and above
What does the compressor and the condenser fan motor have in common?
The COMMON START AND RUN windings
Where does the START wire go for you condensing fan and your compressor
On the compressor (blue) wire goes to the HERM on the capacitor and for the condensing fan it would be 1or 2 brown wires that goes to FAN on cap or it will have its own capacitor.
Where does the RUN wires go for your compressor and outdoor fan?
They both go to T2 on the contactor usually yellow.
Where would your COMMON wires go to your compressor and outdoor fan?
They would usually go to your T1 terminals on the contactor
When you see 18 in the model number what’s the tonnage of the unit?
1.5 tons
When you see 24 in the model number what is the size of the unit?
2 tons
When you see 30 in the model number what’s the tonnage of the unit?
2.5 tons
When you see a 36 in the model number what’s the tonnage?
3 tons
When you see a 42 in the model number what’s the tonnage of the unit?
3.5 tons
When you see a 48 in the model number what’s the tonnage of the unit?
4 ton
When you see a 60 in the model number what’s the tonnage of the unit?
5 tons
How would you test a defrost thermostat sensor?
DFT suppose to be normally open. So you would ohm/continuity it out to see if it’s closed or not. And a k temp probe
How would you test a contactor?
You can unplug the 24v and ohm it out which would read around 14ohms. Or check to see if it’s passing power
If the cool on or heat on is blinking what does that mean?
It’s in a 5 minute delay
On a straight cool system and not a heat pump is there a delay?
No
If a air handler does not have a board what does that mean?
That mean it has a Ecm motor for the indoor unit
How can you test a thermostat?
If it’s not operating correctly jump out the wires. If it starts working when you jump it out at the thermostat but it doesn’t work when you operate it it’s your thermostat
How does a float switch usually sit? Open or closed?
Closed
Which circuit do you break to add in a float switch?
Primarily you want to break the R. But in other applications you can use Y. That’s the only two that produces condensation since it builds during cool
How do you wire in a float switch?
One wire you want to wirenut to your 24v source for the transformer and the other you would want to connect to the R on your thermostat wire
If your compressor stops working when you call for cool but your indoor fan works fine what could be the issue?
1.)They have a float/safety switch wired into the Y circuit in the indoor unit
2.)pressure switches at condenser
3.)defrost board
4.) bad contactor
5. Bad compressor
On a condensation line what needs to be added and why?
A pe trap is needed for the line so that the water is able to drain when the ac is running by creating a vaccum
On a heat pump when is the * Y energized, in cooling or heat mode?
Both
If their is high humidity in the house do you set the fan speed lower or higher?
You set it lower
On a heat pump system if you have a txv outside what should the superheat be around?
8-14 degrees
When you look at the subcooling rating at the outside condenser it can be plus or minus by what?
Three
If you have a 32 or below sat temp on the vapor line and the subcooling and superheat is within the plus or minus 3 what’s happening?
Low airflow issue, dirty filter/fan or low fan speed
On a system if you have very high superheat and average subcooling with the sat temp of the vapor line below 32 what’s happening?
A liquid line restriction, bad txv or clogged filter dryer
How would you troubleshoot shoot a Ecm motor?
Check for line and low voltage. So first stick the probes in on the *L and *N to look for line voltage. Then for 24v stick one probe at the common terminal and the other for the fan speed
What are three ways a TXV fails?
1.the bulb lost its charge
2.it’s clogged
3.stuck in the closed position
When working on a ECM motor if the furnace/ Air handler is on that means the motor is not receiving any voltage. True or False?
False if the furnace/ Air handler is on then it’s receiving voltage at the *L and *N wires on the high voltage side always
The Ecm motor does not need 24v to turn on. True or False?
False. A Ecm motor should not turn on unless it gets a signal from the 24v. If it running without that signal you could have a bad motor
True or False there should be continuity across all windings on a fan motor
True if their is no continuity between two windings the motor needs to be replaced and one of your wires is open
Can a thermostat blow a fuse?
Yes
If you have a jumper from *R to *Y and the fuse pops what could be wrong?
- It could be the wires itself going outside
- It could be the contactor
Say your fuse pops every time you have power to *R and *Y how can you tell it’s the wires or contactor?
Well first undo the wire nuts that go to *y and *c that connects the indoor thermostat wire to the outdoor unit. And your jumpers and then add power. If it pops it’s your thermostat wire if not it’s the contactor
When you ohm out your contactor coil how many ohms should you read?
Between 10-20 ohms. If you get anything below 8 it may start to trip the breaker or blow fuse
If you don’t have 24v. What is one thing that is over looked?
Blown fuse
