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GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy ( ACRA ) in Edenvale . He holds a Bachelor of Business Administration and an associate degree in educational administration . He has a National Technical Diploma and completed an apprenticeship with Transnet . He has dual-trades status : refrigeration and electrical . He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018 . Currently he is the SAIRAC national treasurer .
WELCOME TO THE SOLUTIONS PAGE
By Grant Laidlaw
Many people ask for assistance in the understanding of theoretical and practical aspects of the industry . I will endeavour to enlighten . I am going back to basics as I have questions coming in which indicate that the basic understanding necessary to work in industry is not in place .
Riaan asks : Could you please explain the connection of a single phase motor with relay and multi-speed evaporator motors . We are having motors burn out and the suppliers are telling us we are not connecting the supply correctly . Also sometimes we connect a system to a circuit breaker but the breaker trips immediately . Our supplier has informed us that the circuit breaker is not suitable for motor starting , any ideas on this please .
Thanks you for the question , Riaan . Speaking to some of the industries suppliers , this appears to be a common problem . Unfortunately the incorrect wiring of a single phase compressor will almost certainly result in damage / burnt windings .
This in turn leads to warranty claims and some ill feelings as this type of burnout is not covered by warranty . Make one hundred percent sure your connections are correct prior to starting the compressor . In addition , do not supply power to a
Burnt motor winding .
hermetic / semi hermetic compressor while the system is in deep vacuum as electrical damage may occur .
You should have a multimeter and an insulation tester available ( MEGA ). A multimeter does not normally have the
All images Supplied functionality to perform insulation tests . In addition , a clamp type tong tester used to test amperes is a useful tool when testing motors .
Using a multimeter set on the ohms scale and the compressor electrically disconnected , test the motor windings for continuity , see figure below .
Please note : The readings given below are an example . Testing between the Run ( R ) to Common ( C ) connections will give you the lowest reading . Testing between the Start ( S ) to Common will give you the reading with the in-between value and testing between Run and Start will result in the highest reading . This is the highest reading as you are testing across both start and run windings .
At the risk of repeating myself : different compressor makes and sizes will have different readings but the running winding will always have a lower resistance than the starting winding . The two readings added together give the total resistance . This reading identifies the common connection . The resistance of the running and starting windings when added together must be the same as the total resistance . If not , the windings are damaged and the compressor will have to be replaced .
" If all the readings test correct the compressor can be run . Using a tong tester take the ampere reading while it is running . The amp reading should correspond with the ampere rating on the compressor while under operating conditions ."
www . refrigerationandaircon . co . za RACA Journal I April 2023 43