Transcript AutoCAD Architecture 2008: Part I: Getting Started

Always Learning
CHAPTER 12
A/C System Inspection and Diagnosis
OBJECTIVES
After studying Chapter 12, the reader will be able to:
1.
2.
3.
4.
5.
6.
Inspect an A/C system to determine whether it is
operating correctly, and if not, make further tests to locate
the cause of the problem.
Connect a manifold gauge set to an A/C system and
check system pressures.
Determine whether system pressures are normal, and if
abnormal, determine the cause of the fault.
Check a TXV and determine whether it is operating
properly.
Locate the source of a refrigerant leak.
Complete the ASE tasks related to A/C system diagnosis.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
3
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
KEY TERMS
•
•
•
•
•
•
•
•
Back-seat
Compound gauge
Delta T
Electronic leak detectors
Front-seat
Hand valves
Manifold gauge set
Mid-seat
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
•
•
•
•
•
•
•
4
Rub-through
Service hose
Service unit
Shutoff valve
Ultrasonic leak detector
Vacuum pump
Valve core depressor
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
INTRODUCTION
•
If the HVAC inspection has determined a fault in
the A/C system, further checks can be made to
determine the exact cause of the problem.
•
•
This further evaluation usually consists of a check of
system pressures and temperatures while also
checking for unusual noises, vibrations, and smells.
A/C SERVICE REGULATIONS
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
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Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
TECH TIP
•
Remember that the purpose of the A/C system is to
make the evaporator cold, slightly above 32°F (0°C).
We determine its temperature by feeling the suction
line where it reenters the engine compartment; it
should be cold to touch. The suction line warms up as
it goes to the compressor, but it still should be cool to
touch. The discharge line leaving the compressor
should be hot to very hot; use caution when you feel
this line. Remember that the condenser must give up
heat to the ambient air, so it must be hotter than
ambient temperature.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
6
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
A/C PRESSURE CHECKS
•
SERVICE UNITS
•
A service unit contains:
•
•
•
•
•
High- and low-side pressure gauges
A vacuum pump
A refrigerant supply and method controlling the
charge
A method of adding oil to a system
Most modern service units also include:
•
•
A method of recovering refrigerant from a system
A method of recycling that refrigerant for reuse
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
7
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
A/C PRESSURE CHECKS
•
GAUGE SET
•
•
•
ELECTRONIC GAUGE SETS
CHECKING GAUGE ACCURACY
CONNECTING AND DISCONNECTING GAUGES
TO A SYSTEM
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
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Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
TECH TIP
1.
2.
If the protective cap is missing, dirt will enter the port
and valve core, being attracted and trapped by the oil
film. When the system is serviced, this dirt will enter
either the gauge set or the system. Dirt particles can
damage the valves and the gauges in the gauge set,
damage the compressor, or plug small orifices if they
enter the system. An unprotected port should be
cleaned before connecting a hose to it.
Many service fittings are permanently welded onto
the line; some are threaded onto the line and are
replaceable.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
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Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
TECH TIP
•
There are two major types of R-134a
couplers: manual and automatic. Both types
are quickconnect with a ring that must be slid
upward to allow connecting and
disconnecting. Manual couplers have a knob
that is turned inward to depress the service
valve. Do not overtighten this knob, as it can
damage the valve.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
10
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
Why Do Some Systems Have More Than
Two Service Ports?
•
Some systems that use an STV have a second lowside service port to allow the use of a third gauge. A
third gauge is a single, compound gauge, similar to
the low-side gauge, and is often attached directly to a
service hose. The third gauge is usually attached to
the third service port, which is downstream from the
STV, closer to the compressor. Comparison of the
low-side pressure with that of the third gauge allows
the technician to determine whether the STV is open
or closed.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
11
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
What Is a Service Valve?
•
Some early A/C systems (R-12) use service valves at the service
ports. A service valve has a stem that can be rotated using a 1/4inch square socket or box wrench. This valve is set to one of
three positions: back-seat , mid-seat , or front-seat . During
normal operation the valve is kept in the back-seat position: This
closes the service port while the compressor port is left open.
During service operations the valve is mid-seated: This opens
both the compressor port and the service port. During some
special operations the valve is front-seated: This closes the
compressor port while the service port is left open. A service
valve is fitted with protective caps for both the service port and
the valve stem. While working with service valves, open-end
wrenches, adjustable wrenches, and pliers should never be used
on the valve stem. These tools will ruin the 1/4-inch square stem
and prevent the use of the proper wrench.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
12
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
TECH TIP
•
As the R-12-style service hose is being connected to
a Schrader valve port, refrigerant often escapes
because the valve depressor usually makes contact
with the valve stem before the seal ring contacts the
seat. This leak can be reduced by using the following
procedure: Thread the knurled nut on the port one or
two turns, grip the hose and push it quickly and firmly
against the port, and tighten the nut to hold the hose
in place. The knurled nut should be tightened only
finger-tight. The seal and seat can be damaged if
pliers are used. If the seal leaks while finger-tight, the
sealing ring in the hose end should be replaced.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
13
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
PERFORMANCE TEST
•
A performance test is used to determine whether
the A/C system is operating properly and to
indicate what is wrong if the system is not
operating normally.
•
Inspection checklists are TS 5 and TS 6 in the
NATEF Correlated Task Sheets.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
14
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
PERFORMANCE TEST
•
SYSTEM TEMPERATURES
•
•
•
•
•
•
•
•
THERMOMETERS
MEASURING RELATIVE HUMIDITY
INTERPRETING SIGHT GLASSES
INTERPRETING PERFORMANCE TEST
READINGS
ABNORMAL CONDITIONS
VERIFYING REFRIGERANT CHARGE LEVEL
ON-VEHICLE TXV TESTS
ELECTRONIC DIAGNOSTIC TOOL
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
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Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
TECH TIP
•
An infrared thermometer with a flexible probe
can be used to measure the temperature of
an item that is difficult to get to.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
16
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
TECH TIP
•
A direct-reading, electronic humidity tester is
available that provides fast, easy humidity
measurements. Technicians can quickly
measure in-vehicle humidity, which should be
about 30% to 50% RH in vehicles with A/C
systems that are operating properly.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
17
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
A/C SYSTEM REFRIGERANT LEAK TESTS
•
•
•
ELECTRONIC LEAK DETECTOR CALIBRATION
EVAPORATOR INSPECTION
VACUUM PUMP LEAK TESTS
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
18
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
TECH TIP
1.
2.
3.
Check the high side for leaks right after shutting the engine and
system off while the pressure is the highest.
To increase system pressure for leak checking, heat the
accumulator or receiver–drier. A heat gun can be used or you
can wrap the unit with a small heating pad.
Some technicians consider the Schrader valve and service port
cap as expendable items. They replace these parts when
making a major service to a system. A faulty Schrader valve can
be removed by unscrewing it just like a tire valve; in some
cases, a tire valve service tool can be used. A special service
tool is used in very tight locations. A new A/C Schrader valve
should be installed; tire valves will not work properly.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
19
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
TECH TIP
1.
2.
Some R-134a service ports are threaded into
the metal line. A damaged service port can
often be replaced by unscrewing the port
from the line and installing a new one.
A leaking high-pressure relief valve can be
replaced using a new valve and gasket.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
20
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
SUMMARY
1.
2.
3.
4.
Technicians use system pressures and
temperatures to determine if a system is working
properly and what is causing the problem if the
system is not working properly.
The pressure in different sections of a system is
linked to the temperature of that section.
Service equipment such as manifold gauge sets
and service units must be dedicated to a single
refrigerant type.
Technicians check their pressure gauges
periodically to ensure that they are working
properly.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
21
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
SUMMARY
5.
6.
7.
8.
9.
Performance tests follow a set procedure.
High-side pressure is related to ambient
temperature.
Pressures that are higher or lower than normal
indicate the nature of the system’s problem.
The best way to ensure that a system has the
proper refrigerant charge is recover the
refrigerant and recharge it to the specified
amount.
Several types of leak detectors can be used to
locate refrigerant leaks.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
22
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
REVIEW QUESTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
An A/C gauge set contains a(n) ______________ ______________ and a(n)
______________ ______________ pressure gauge, at least two hand valves,
and ______________ ______________ .
An A/C service unit will include ______________ ______________ , a(n)
______________ ______________ , and a(n) ______________
______________ .
An A/C service unit can also include equipment to ______________ and
______________ refrigerant.
A low-side, R-12 service port is the same as a 1/4-inch ______________
______________ .
A high-side, R-134a service port is ______________ than the low-side port,
and both ports use a(n) ______________ ______________ style coupler.
The low-side gauge and hose are colored ______________ , and the high-side
gauge and hose are colored ______________ .
When the hoses are connected to an R-12 system on a 70°F day, both gauges
should read about ______________ ______________ .
In an R-134a system with normal operation, the low-side pressure should be
about ______________ psi, and the suction line should be ______________ .
In an R-134a system with normal operation, the discharge line should be
______________ , and the high-side pressure will ______________ as
ambient temperature increases.
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
23
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
REVIEW QUESTIONS
10.
11.
12.
13.
14.
15.
16.
17.
18.
Bubbles are expected to appear in the sight glass during ______________
______________ .
High relative humidity can cause ______________ high-side ______________.
Low pressure on the low and high sides is commonly caused by
______________ ______________ .
A faulty compressor can cause ______________ low-side pressure and
______________ high-side pressure.
The refrigerant charge level can be verified by checking the ______________
and ______________ of the refrigerant at the condenser outlet.
The most popular refrigerant leak detectors used today are ______________
______________ and ______________ ______________ .
A system should have a pressure of at least ______________
______________ when checking for a leak.
The leak detector probe should be moved along about ______________
______________ from the location being checked at a maximum rate of
______________ inch(es) per second.
A fluorescent trace will show up better if you wear ______________
______________ .
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
24
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
1. Technician A says that you should begin A/C
problem diagnosis with a thorough HVAC system
inspection. Technician B says that from the
inspection it can be determined what type of
system the vehicle has. Who is correct?
a.
b.
c.
d.
A only
B only
Both A and B
Neither A nor B
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
25
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
2. Technician A says that oily residue on a fitting or
hose can indicate a refrigerant leak. Technician B
says that this residue will not affect a leak
detector. Who is correct?
a.
b.
c.
d.
A only
B only
Both A and B
Neither A nor B
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
26
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
3. When a system is operating correctly, the lines
and hoses on the high side should be cool to the
touch.
a.
b.
True
False
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
27
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
4. Technician A says that pressure checks are one
method of diagnosing A/C problems. Technician B
says that trouble trees are used only for
mechanical problems. Who is correct?
a.
b.
c.
d.
A only
B only
Both A and B
Neither A nor B
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
28
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
5. While discussing a manifold gauge set, Student A
says that the high-side service hose is blue.
Technician B says that the low-side pressure
gauge goes up to 750 psi. Who is correct?
a.
b.
c.
d.
A only
B only
Both A and B
Neither A nor B
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
29
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
6. Technician A says that the manifold gauge set for
R-12 can be used on all systems. Technician B
says that R-134a systems use service ports with
metric flare threads. Who is correct?
a.
b.
c.
d.
A only
B only
Both A and B
Neither A nor B
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
30
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
7. On a system that uses service valves, the valve is
kept in the ______________ seated position for
normal operation.
a.
b.
c.
d.
frontbackMid
None of these
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
31
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
8. An R-12 system is shut off, and the ambient
temperature is 70°F. The evaporator pressure
should be about ______________ .
a.
b.
c.
d.
50 psi
70 psi
83 psi
100 psi
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
32
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
9. In most R-12 systems that use an STV, the
normal low-side pressure should be about
______________ .
a.
b.
c.
d.
15 to 20 psi
15 to 30 psi
28 to 30 psi
over 35 psi
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
33
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
10. High-side pressure is affected by
______________ .
a.
b.
c.
d.
ambient temperature
fan clutch operation
refrigerant charge level
All of these
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
34
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
11. A faulty A/C system has a high low-side pressure
and a high high-side pressure. Technician A says
that the system is probably starved. Technician B
says that the system has a bad thermostatic
switch. Who is correct?
a.
b.
c.
d.
A only
B only
Both A and B
Neither A nor B
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
35
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
12. ______________ can be used to locate
refrigerant leaks.
a.
b.
c.
d.
Soap and water
Flame-type testers
Electronic testers
Any of these
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
36
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
13. The engine should be running while the
technician checks for leaks.
a.
b.
True
False
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
37
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.
CHAPTER QUIZ
14. Technician A says that the system should be
operated after injecting fluorescent dye into it.
Technician B says that wearing yellow-tinted
goggles can help you find the dye traces, and this
also protects your eyes. Who is correct?
a.
b.
c.
d.
A only
B only
Both A and B
Neither A nor B
Automotive Heating and Air Conditioning, 6/e
By Thomas S. Birch
38
Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson Education
Upper Saddle River, NJ 07458 • All rights reserved.