Refrigeration & Air Conditioning Technology, 8e - xvii
result. The vibration of the compressor will vibrate the conC. using
trol tube and rub a hole in the tube or one of the refrigerantcircuit. e total of the highfa-vnolmotor.
rage in th
lines if they are not kept separate.
age at th
8. The se
e limit co
sion in th
d with fo
The electrical section of the control will usually havepow
systems as xt has primarily
9. True or start and stop th igh or low) voltag
set of contacts or a mercury switch to stop and start some False: A pa
pumps. T e secondary heat may be the prim ost comencer can s.
of strip he
component in the system. The electrical contacts are often
start or st
enclosed and cannot be viewed, so visual inspection is not
customer always listen to th with heat
of the pr
n often le
ith a sim
ad you to stomer
possible. When a problem occurs, look for frayed wires
ng for he
burned wire insulation adjacent to the control. The mercury
in mercury switches may be viewed through the clear glass
open fu the valveitcis
is 30 psig. No wonder
relieving the pressure; itPossib
se or brea
enclosure. If theCharts
mercury becomes dark, the tube is allowlose disc tell
r the technician C
is too high. The boiler is hot, ke
ing oxygen to enter the space where the mercury makes and
fuse or re
if it is too hot. The burner
se link op
e why it
breaks the electrical
is occurring. In
cian decides that
this may be a pressure
of opened. r and
this case, the switch should be replaced because the switch
a temperature problem. oltage wiring or co
n at fuse
across the oxidation
and so be closed at all
repair or reguConlooks
for and finds the water
times. This could prevent a boiler from shutting off, allowing
lating valve, which is in the supply
ntrol-volkeeps the supply water
overheating to occur.
s and sa
ent burndue to a leak. The
when there is Po
a rtloss el
pressure is 30 psig with a relief valve setting ofSe30
ove. if the
Correct voit would
supply water were allowed directly into the boiler,
push the pressure past the design pressure of the system,
which must be less than 30 psig. if the pressure were above
this, it would cause the pressure relief valve to relieve the
pressure and dump water from the system until the pressure
SERVICE CALL 1
A customer calls indicating that the boiler in the equipment
The technician shuts off the water valve leading to the
room at a motel has hot water running out and down the
boiler makeup system and bleeds some water from the sysdrain all the time. Another service company has been pertem until the pressure at the boiler is down to 15 psig. He
forming service at the motel for the last few months. The
then adjusts the water regulating valve to a lower pressure
problem is that the water-regulating valve (boiler water feed)
and opens the supply water valve to allow water to enter
is out of adjustment. Water is seeping from the boiler's presthe system. The technician can hear water entering through
sure relief valve, Figure 14.66.
the water regulating valve. in a few minutes, the water stops
The technician arrives at the motel, parking alongside the
entering. The pressure in the system is now adjusted to
building so as not to block the Section
or the motel's reg18 psig and all is well.
Theory of Heat
istration parking areas. When the property manager comes
in this example the problem is that a mechanical automatic
The compound gauge on
the left reads
isprescausing another control to show that the system has
psia, add 15 psi (atmospheric pressure) to 50 psig to get 65 psia.
sures above and below atmospheric pressure. The high-pressure gauge on
duces himself and hands him his company's
if left unexamined, the problem might seem to be
the right will
up to 800 psi. The center
gauge is a vacuum
which is used for system evacuation (see Unit 8 for more on this
After asking some preliminary questionsgauge,
that the relief valve is defective because water is seeping out
and the manager
of it. This is not the case; the relief valve is doing its job. The
Callsgo to the boiler room. Once
there, the tech notices that, as the customer said, water is
water regulating valve is at fault.
The technician shows the motel manager what the probcalls
causing a very situational
lem was, how it was corrected, and completes the paperwork
is in in
before leaving for another call. The technician makes a point
may find themselves. In many instances, the solution is
provided in the text, and in others the reader must decide
what the best solution should be. These solutions are
provided in the Instructor's Manual. The Service Technician
Calls will now incorporate customer relations and technior reference point. If you want to know what the absolute
must add the atmospheric pressure to the
gauge reading. For example, to convert a gauge reading of
50 psig to absolute pressure, you must add the atmospheric
pressure of 14.696 psi to the gauge reading. Let us round off
Gauges provided by Appion Inc. Photo by Eugene Silberstein
14.19 SERViCE TECHNiCiAN
14.696 to 15 for this example. Then 50 psig 1 15 5 65 psia
(pounds per square inch absolute), figure 1.25. New generation gauges are of the digital variety, figure 1-26.
Thermometers measure temperature. Four temperature scales are Fahrenheit, Celsius, Fahrenheit absolute
(Rankine), and Celsius absolute (Kelvin).
Molecules in matter are constantly moving. The higher the
temperature, the faster they move.
The British thermal unit (Btu) describes the quantity of
heat in a substance. One Btu is the amount of heat necessary to raise the temperature of 1 lb of water 1°F.
The transfer of heat by conduction is the transfer of heat
from molecule to molecule.
The transfer of heat by convection is the actual moving of
heat in a fluid (vapor state or liquid state) from one place
Radiant heat is a form of energy that does not depend on
matter as a medium of transfer. Solid objects absorb the
energy, become heated, and transfer the heat to the air.
Sensible heat causes a rise in temperature of a substance.
Latent (or hidden) heat is heat added to a substance
that causes a change of state and does not register on a
Specific heat is the amount of heat (measured in Btu)
required to raise the temperature of 1 lb of a substance
1°F. Substances have different specific heats.
Pressure is the force applied to a specific unit of area. The
atmosphere around the earth has weight and therefore
Barometers measure atmospheric pressures in inches of
mercury. Two of the barometers used are the mercury and
Gauges have been developed to measure pressures in
enclosed systems. Two common gauges used in the airconditioning, heating, and refrigeration industry are the
compound gauge and the high-pressure gauge.
1. Temperature is defined as
A. how hot it is.
B. the level of heat.
C. how cold it is.
D. why it is hot.
State the standard conditions for water to boil at 212°F.
List four types of temperature scales.
Under standard conditions, water freezes at _____°C.
Molecular motion stops at _____°F.
The Summary appears at the end of each
unit prior to the Review Questions. It can be
used to review the unit and to stimulate class
Review Questions follow the Summary in
each unit and can help to measure the
student's knowledge of the unit. There are a
variety of question types-multiple choice,
true/false, short answer, short essay, and