WAEC Air Conditioning(Ac)/Rerigeration May/June 2016 Questions and Answers

WAEC Air Conditioning(Ac)/Rerigeration May/June 2016 Questions and Answers

Question 1

State the function of the following accessories of a refrigeration system: overload, high pressure cut out switches, low pressure cut out switches, anti-freeze, thermostats.

Observation

The expected responses are:

(a)        FUNCTION OF THE FOLLOWING ACCESSORIES OF A                                                          REFRIGERATION SYSTEM OVERLOAD:

–           This is a device either temperature, pressure or current operated which will stop operation of unit if dangerous condition arise.

–           It is used to protect the compressor from overheating

1. HIGH PRESSURE CUT OUT SWITCHES:

–           This is  an electrical control switch operated by the high side    pressure which automatically opens electrical circuit if too high pressure is reached.

–           It is used to stop the system when the pressure exceeds safety limit.

1. LOW PRESSURE CUT OUT SWITCHES:

–           This is a device used to keep low side evaporating pressure from                                                     dropping below certain pressure.

–           It is used to stop the system when evaporation or suction pressure                                                   becomes low.

–           It also sometimes causes the compressor to produce a high vacuum at                                             high speed.

(iv)       THERMOSTAT:
–           This is a device that is used to control the temperature of a refrigerator                                           system.
–           This is a device which senses ambient temperature conditions and in turn                                       acts to control a circuit

(b)        TYPES OF REFRIGERATOR

1. Single door refrigerator.
2. Double door refrigerator
3. Single compressor
4. Multi compressor.

(c)       Refrigerant Blend:
–           Refrigerant blend is the liquid mixture of refrigerant which
exhibit a constant maximum and minimum boiling point  and these                                                 mixtures act as a single refrigerant.
–           It is also the combination of two or more refrigerant to produce a single                                         refrigerant.

Majority of the students were able to answer the questions correctly.

Question 2

What control measure should be taken when there is a leakage of refrigerant?; State three safety precautions to be observed in a workshop to avoid electric shock; Define matter; State Boyle’s Charles law?

Observation

The expected response was:

CONTROL MEASURE TO BE TAKEN WHEN THERE IS LEAKAGE OF
REFRIGERANT.

•  Ensure that the room is thoroughly ventilated
•  Recover the refrigerant.
•  Locate the point of leakage and rectify

(b)        SAFETY PRECAUTIONS TO BE OBSERVED TO AVOID ELECTRICAL
SHOCK

(i)        Wear safety apparel such as glove and boot.
(ii)        Do not operate electrical machine unless you know how to stop it.
(iii)       Do not touch electrical operated machine with wet hand.

• Always concentrate when working on electrical operated machine.
• Do not remove protective guide from the machine when working.
• Do not touch naked wire with bare hand.

 

(c)        Matter is  anything that has weight and occupies space.

(d)       Boyle’s Law:  States that the volume of a given mass of gas is inversely proportional to its absolute pressure provided the temperature remains constant.

Mathematical expression

P1 V1   =         P2 V2

Majority of the candidates avoided this question and of the few that attempted only a candidate got it right.

Question 3

Observations

Majority of the candidates avoided this question and of the few that attempted only a candidate got it right.

Question 4

State the four basic principles guiding a refrigeration technician during mechanical operations in the workshop?

Observation

The expected response is:

FOUR BASIC PRINCIPLES GUIDING A REFRIGERATION TECHNICIAN DURING MECHANICAL OPERATION IN THE WORK SHOP

(i) Adequate knowledge of the work/what need to be done

(ii) Knowledge of safety/follow approved safety procedure

(iii) Selection of appropriate tools and materials

(iv) Keep all refrigeration mechanism clean and dry Majority of the students responded correctly to this question.

Question 5

What is marketing? State three functions of marketing. Explain the terms, credit, loans.

Observation

 

The expected response is:

(a)        MARKETING:
–           Marketing means all business activities that assess as well as                                               influence the type of goods and services which consumer demand and                                ensure that such good are produce and brought to the consumer at the                                 right price, place and time.

–           Marketing has to do with the particular means through which goods are                             brought from the producers to the consumers.

–           It is also the activities and process of creating, delivering and exchanging
offerings that have values for customers, clients, partners and society at large.

(b)        FUNCTIONS OF MARKETING:

–    Determination of products
–    Determination of quantity of goods
–    Determination of time of demand
–    Advertising of products.
–    Making sales of products
–     Choice of means of distribution
–     Pricing policy of goods
–     Determination of place of sales of goods
–     Determination of storage of goods.

(c)        EXPLANATION OF THE FOLLOWING TERMS

1. CREDIT:

 

–            Credit refers to sales in which the seller allows the buyers to take possession of goods and services which the buyer will pay for in a              future date.(this is called credit sales)

–            Credit can also refers to a situation where a person called the borrower is given a sum of money by another person called the lender, which the borrower has to refund  in a stated future date.

1. HIRE PURCHASE:

This type of credit sales is for very expensive goods such as motor vehicle, machine and television sets. The buyer has to pay initial deposit to the seller and take the goods home for his/her use with the agreement to pay the balance amount in a monthly installment.  At any time he default to pay the monthly installment, the seller can reclaim the ownership of the goods.  Until the buyer has paid the last installment, he is regarded as having hired the goods from the seller.

Majority of the candidates who attempted this question answered it correctly.

General Comments

The contents of the paper were of standard. The paper was adequate in score and met the expectations of the candidates.

Majority of the candidates responded correctly to the questions.

The performance of the candidates in this year’s examination was better than the performance over the years.

The scores of the candidates were well above average.

Candidates’ Weakness

Candidates possessed poor computation skills. About five candidates attempted the question on calculations but only one of them got it right.

(2)       SUGGESTED REMEDIES FOR OVERCOMING WEAKNESSES

The following were the suggestion made if the weaknesses are to be remedied:

1. 1. 1. teachers should intensify efforts to teach the students more calculations in the trade.
      2. students should study the calculation aspect of the trade to compliment the efforts of the teacher.

Candidates’ Strength

The candidates did very well on the questions requiring them to recall facts.