exam fail!

[kaspastarr]

ok i just failed my exam by 2 questions. you need to get 60% i got 62.5% but i still failed since its split into 2 sections. :(
a bit pissed of really, but i decided not to get down about it (even thout its £27 for a resit)
i thought you can either mope around or get streight back on the wagon and try and remember the questions you had trouble with while there still fresh on your head.

SO

i wanted to ask if any one could explain some of the following things.

1. EPR (evap pressure regulator) = where there used why, how??? any info.

2. Mixing boxes (for air i think) any info of how there operated

3. Pumped liquid recirculation system??

4. Equalising line?

5. Hot gas (defrost) just general info.

6. TEV (the gas that operated it) i answers water ammonia) but i know thats wrong. just the gases that the tev has inside it and resons for different gasses if they are different.

7. Electric defrost heater.
the question was
if one heater gos down what will happen in a system.
a. part icing of the coil
b. lots of water will form
c?
d?
sorry not much info here :/

8. FAN DELAY SWITCH???
why is it used, how does it work??

9. Oil seperator, how does it work??

10 MOP type TEV???

and here are some questions i remembered/ wrote down

to provide greater cooling capacity cappilery tube resrictors:
a. should be shorter with a bigger bore(i think its A)
b. would increase flow automatically due to higher condenser pressure
c. should be long but with a bigger bore
d. should be connected directly to evap inlet.

an EPR is used in central air conditioning systems:
a. so that the off coil tempretures do not fall below the human comfort control
b. because full humidity control requires controlof minimum coil surface tempreture
c to prevent the water in the air washer from freezing
d to prevent condensation in the mixing chamber

(also what is a mixing chamber??)

the slide valve on a twin screw compressor gives step-less capacity control by:
a. changing the position on the rotors where compression starts
b. throtteling vapour to a standby compressor inlet
c. throtteling liquid to a standby compressor inlet
d. acctuating dampers to by pass refrigirant around the teh evaporator.
(i answed b but i know the answer is A but i dont know why its A can any 1 explain??)

On large compressor systems, liquid injection into the suction line is used to:
a. prevent the system from nuicence tripping on LP
b. increase discharge pressure in low ambiant conditions
c. prevent overfilling of the liquid reciever on low load conditions.
d. reduce the discharge tempreture by reducing the suction tempreture.
(i know its D but i dont fully understand why)

which one of the following compressors is NOT a displacment compressor.
a. centrifugal
b. scroll
c. screw
d. rotary
(im not sure i remember this question correctly i think it means what one cant be a inverter compressor??)

ok ANY help with ANY of the questions will be MORE than appreciated. im not just looking for hand outs on teh answers, i want to understand it. like i said ANY help.
thanx for helping me on the last questions guys ESP viking your a top dude.
i just have to resit this stupid one.

64

[Chunk]

I`ll start off with the EPR question

An Epr is installed in the suction line at the evaporator outlet and is set to stop the evaporator temperature from going below a certain point.
For example; if you dont want the evap temp to go below -6*c you can set the valve so that if you have a saturated suction temperature that is less than this,lets say -12*c, the valve will stop it from going too low.

The tev mop question

Thermostatic expansion valves can contain one
of three different types of charge:
1. Universal charge
2. MOP charge
3. MOP charge with ballast, standard for Danfoss
expansion valves with MOP.
Expansion valves with Universal charge are used
in most refrigeration systems where there is no
pressure limitation requirement and where the
bulb can be located warmer than the element
or at high evaporating temperature/evaporating
pressure.
Universal charge means that there is liquid
charge in the bulb. The amount of charge is so
large that charge remains in the bulb irrespective
of whether the element is colder or warmer than
the bulb.
Expansion valves with MOP charge are typically
used on factory-made units where suction
pressure limitation on starting is required, e.g.
in the transport sector and in air conditioning
systems.
All expansion valves with MOP have a very small
charge in the bulb.
This means that the valve or the element must be
located warmer than the bulb. If it is not, charge
can migrate from the bulb to the element and
prevent the expansion valve from functioning.
MOP charge means limited liquid charge in the
bulb.
“MOP” stands for Maximum Operating Pressure
and is the highest suction pressure/ evaporating
pressure permissible in the evaporator/suction
line.
The charge will have evaporated when the
temperature reaches the MOP point. Gradually,
as the suction pressure rises, the expansion valve
begins to close at approx. 0.3/0.4 bar below the
MOP point. It becomes completely closed when
the suction pressure is the same as the MOP
point.
MOP is often called “Motor Overload Protection”.

[The Viking]

Hmm,

Now I'm upset!

I even told you to read the Danfoss manual...

Youth of today!

Ho Hum, you can lead a horse to the water but not force it to drink I suppose.


:rolleyes:

Never mind, better luck next time.
:cool:

[kaspastarr]

Hmm,

Now I'm upset!

I even told you to read the Danfoss manual...

Youth of today!

Ho Hum, you can lead a horse to the water but not force it to drink I suppose.


:rolleyes:

Never mind, better luck next time.
:cool:i went to danfoss but all i could find was a stupid basics of refrigiration cycle.

[The Viking]

45, when should an externally equalised TEV be used?

a) When there is a liquid distributor on the evaporator coil
b) When there is NOT a liquid distributor on the evaporator coil* (Have a look at my website www.the-viking.eu (http://www.the-viking.eu/) and download Danfos' TEV guide, very good reading before your test)
c) To achieve a very low evaporating temperature


..........[10]

[Chunk]

http://www.danfoss.com/BusinessAreas/RefrigerationAndAirConditioning/EducationAndTraining/Fitters+Notes.htm

Download which one you want to read.:D

[Brian_UK]

Mixing Box In a ducted system there would be two ducts, one with heated air and one with cooled air.

The discharge temperature would be controlled by mixing the hot/cold air flows to provide the required temperature.

EPR In addition to the answer given above you would also use EPRs when you have more than evaporator on a system and they may be operating at different temperatures.

For example a cool room room at +10, a cold room at +5 and a freezer at -20. The EPRs would each be selected for the required temperature so the the overall system could perform at -20 but the warmer rooms would not be allowed to go that cold.

[kaspastarr]

thanx guys also does a EPR cut our on low evap pressure??
64

[Pooh]

Obviously doing the Level three technical certificate were are you studying it as looking at the questions you have posted you were not ready to take the exam also getting the answers to these does not guarantee you passing next time as you may get a completely different set of questions. Dont rely on the answers you have been given go back to your books and learn the basics and you may stand a chance.

Ian

[kaspastarr]

well i passed the first exam which more than 50% of the class failed, and as for me asking questions on here, im not doing it so i can copy them and pass the exam, im doing it so i can learn, even if i failed the 2nd exam again but i learned more about the parts where i failed, ide be happyer for it. im still learning as i suppose i always will be, and failing an exam only makes me want to learn more, there is so much taught at collage that is not relivant, that its hard to learn every thing, also the method that is taught is difficult to understand sometimes, and we all learn at different paces, im still just trying to learn ok so give mem a break.
64

[taz24]

well i passed the first exam which more than 50% of the class failed

im still just trying to learn ok so give me a break.
64


Well done for the first one most of the questions you asked were from the first exam (301) the technical one and as you said you have passed that one so well done.

Good look for the next exam and if you only missed by a few points I'm sure you will be fine.

Don't take Pooh's responce as a criticism his advise is very good.
You seem to have your priorities right and you will get through the exam, all Pooh is saying is don't try to learn the answers to the questions.
You need to know how the system works so you can relate things to each other, only then will you know sufficient to pass the exam. Learning the answers to the questions only proves that you can remember things.
I know you were not asking for that reason but at level 3 not knowing where the EPR is situated would suggest lack of genral knowledge and that is what Pooh pointed out.

Well done for what you have done and all the best for the next exam..

taz.

[Chunk]

well i passed the first exam which more than 50% of the class failed, and as for me asking questions on here, im not doing it so i can copy them and pass the exam, im doing it so i can learn, even if i failed the 2nd exam again but i learned more about the parts where i failed, ide be happyer for it. im still learning as i suppose i always will be, and failing an exam only makes me want to learn more, there is so much taught at collage that is not relivant, that its hard to learn every thing, also the method that is taught is difficult to understand sometimes, and we all learn at different paces, im still just trying to learn ok so give mem a break.
64

I agree with you totally.When i was at college(the last of the city and guilds qualifications),the whole of the theory was aimed at the design side of the business.The first year was practical and that was cool,but i came out the other end totally baffled.I hope they will change what people learn at college.Even my own apprentice failed his exams,and he is top notch.(He gets dunked in an oil drum if he fails again though;))

[alphi]

Hi,

Failing the exam is not a failure. It's a gift of challenge that you need to learn more...... soon you will be more than us...

kr,
alphi