chap51 pps Automotive technology at University of Cambridge

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Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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OBJECTIVES:
After studying Chapter 51, the reader should
be able to:

•
•
•

Perform heating, ventilation, and airconditioning (HVAC) system service
procedures.
Identify precautions that should be adhered to

during HVAC system service.
Discuss proper evacuation and refrigerant
recovery procedures.

Continued
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OBJECTIVES:
After studying Chapter 51, the reader should
be able to:

•
•

List the steps needed to be performed to
retrofit an older R-12 system to R-134a.
Describe air-conditioning parts replacement
and service procedures.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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KEY TERMS:
air dam
fin comb
noncondensable gas

O-ring seal
quick-disconnect valve
schrader valve • service cap

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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BLOWER MOTOR SERVICE
Heater­related services include these components and operation:
Blower motor and construction  If the blower motor is not 
functioning, the switch, resistors, or blower motor itself may 
need to be replaced. If the resistors are found to be defective, 
then double­check that the current draw of the blower motor is 
within factory specifications. One of the most common reasons 

for a defective blower motor resistor is a defective blower motor 
that has worn bushings and draws more than normal current 
(amps).
Relays and switches  Switches and relays can be tested by 
proper operation and replaced if needed. Always follow the 
vehicle manufacturer’s recommended replacement procedures.
Continued
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COOLING SYSTEM SERVICE
Cooling System Thermostat Replacement  A defective (stuck open) thermostat can cause a 
lack of heat from the heater. If heat “comes and goes,” check coolant level in the radiator before 
replacing the thermostat. When replacing the thermostat, always follow the vehicle 

manufacturer’s recommended procedures and use the designated coolant.
Heater Hose Replacement
Check for signs of deterioration and
replace as needed. Follow vehicle
manufacturer’s recommended
procedures.

Figure 51–1 Some heater hoses are best inspected
by hoisting the vehicle and inspecting them from
underneath the vehicle as shown.
Continued
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Use the Same Length Heater Hoses
Heater hoses are designed to supply warm coolant from the engine’s
cooling system to the small radiator called the heater core inside the
vehicle. Because the heater hoses attach to the engine and the engine
moves on its mounts during operation, the heater hoses are long enough
to allow the engine to move without causing stress to be applied to the
heater core. The extra length also helps to prevent engine vibration from
being transmitted to the heater core and the interior of the vehicle. When
replacing heater hoses, always use the old hoses as a guide and use the
same length hoses. Also, route the replacement hoses in the same
manner as originally designed, again, to help reduce the stress to the
heater core.

Cooling Fan  Inspect for dents, nicks, or other faults that can cause 
a vibration or reduce airflow through the radiator. Check the viscous 
fan clutch for leakage of silicone fluid and replace if needed.
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Check the Air Dam if Overheating Occurs
The air dam under the front of the vehicle is designed to force air to flow
upward and through the radiator rather than travel underneath the vehicle.
If this air dam is broken or damaged due to contact with a parking block or
other object, the engine may overheat.

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REFRIGERANT RECOVERY PROCEDURES
Leak Repair Procedures  After a leak has been found, the 
refrigerant should be recovered and the faulty part repaired or 
replaced. Leaks at joints may need a replacement O­ring. Often, the 
leak is at a component such as the evaporator, condenser, or 
refrigerant line. Leaking components are usually replaced rather 
than repaired.
Refrigerant should be recovered and not allowed to be discharged 
into the atmosphere. A refrigerant recovery unit should be used to 
remove the refrigerant from the vehicle, and it should be stored in a 
container until it can be recycled.
See Figures 51–2 and 51–3.
Continued
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Figure 51–2 (a) A typical automotive air-conditioning service machine that is capable of
handling both CFC-12 and HFC-134a systems. (b) HFC-134a systems use quick-disconnect
fittings that are larger than those used for CFC-12 systems.

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During the recovery process, any refrigerant oil removed is separated 
from refrigerant and allowed to flow into a container where it can be 
measured. The correct total amount of lubricating
oil must be added to the system to protect the compressor.

Figure 51–3 (a) Refrigerant oil must be retrieved and measured when the refrigerant is
recovered from the system. (b) A rubber O-ring is used to indicate the level of refrigerant oil
already in the container. The exact same amount of refrigerant oil must be installed as was
removed when the system is recharged.
Continued
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Repairs or Replacement of Components  After all refrigerant has 
been removed from the system, repairs can be accomplished.
The evaporator can now be removed from the vehicle and replaced. 
If the system has been opened to the atmosphere for a length of time 
(over 24 hours), most experts recommend replacing the drier to help 
prevent the possibility of moisture being trapped in the system.

After repairs are completed, the system should then be evacuated.

NOTE: Be sure to follow all instructions regarding the amount of oil that
needs to be added to the system if components have been replaced.

Continued
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Refrigerant Line Connections  Must meet three requirements:
 The connection must be vapor tight.
 The connection must be easy to disconnect and reconnect.
 The seals must withstand rapid and extreme temperature 
changes.

The O­ring seal is part of a fitting that holds the ends of two 
refrigerant lines or hoses together inside a connector. O­rings
form the seal between the lines or hoses and the connector.
O­rings are made of highly saturated nitriles (HSN) or neoprene 
rubber and remain flexible over a wide range of temperatures. The 
O­ring must be lubricated with clean refrigerant oil before assembly 
to ensure a good seal. Be careful not to crimp the O­ring during 
installation.
Continued
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Figure 51–4 O-rings are usually made of neoprene rubber or highly saturated nitriles (HSN) to
withstand high temperatures and flexing. O-rings should be changed during a retrofit

procedure.

Replace the O­ring seals at all connections when you retrofit a 
system to R­134a. This ensures any traces of R­12 or its oil absorbed 
in the O­ring cannot enter the new system.
Continued
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A variation on the O­ring seal is Ford’s spring­lock coupling.

Figure 51–5 A Ford spring-lock coupling.

It uses two O­rings mounted on the small end of the refrigeration 

line. 
Continued
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The end of the joining refrigeration line is flared to slide over the 
two O­rings. A circular garter spring holds the connection together. 
You need a special tool to disconnect the coupling. 

Figure 51–6 A special tool is needed to remove and install the Ford spring-lock coupling.

Continued
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Service Valves  Provide entry to the system when it is necessary to 
add or discharge refrigerant. The Schrader valve is used on R­12 
systems. Quick­disconnect valves are used on R­134a systems. Each 
type of refrigerant has its own unique fitting and valves have plastic 
coverings called service caps. 
Figure 51–7 The service cap O-ring becomes the primary seal if the service valve leaks.

Continued
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Schrader Valves For years, R­12 systems have used the Schrader 
valve, similar to a tire valve. Internal pressure holds Schrader valves 
closed. There is also a small spring to keep the valve seated if the 
internal pressure becomes insufficient.
When the service connection is made, 
the depressor in the end of the service 
hose or service coupling, presses on a 
small pin inside the valve, forcing the 
valve open. 
Figure 51–8 A depressor pin on the gauge set opens
the Schrader valve when the connection is almost
completely tightened. This prevents accidental
refrigerant discharge.

The high­side service valve on R­12 
systems is smaller and has different 

threads than the low­side valve. 
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Refrigerant Can Be Hazardous
Always wear safety glasses and protective gloves when servicing any
automotive air-conditioning system. If refrigerant escapes, it can freeze
skin or cause blindness if liquid refrigerant were to get into the eyes.

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EVACUATION PROCEDURES
Evacuation means that a vacuum will be applied to vaporize any 
moisture that may be in the system. Although water boils at 212°F 
(100°C) at sea level, it can boil at much lower temperatures when 
the pressure is reduced.
It is important to evacuate the system to at least 26 in. Hg of 
vacuum for at least 45 minutes to be assured that all of the 
moisture has been removed.
For best results, the vacuum should be higher than 29 in. Hg. The 
higher the vacuum and the longer that it is allowed to evacuate, 
the better.

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Use a Micron Vacuum Gauge for Best Results
A typical vacuum gauge reads in inches of Mercury (in. Hg) and the
recommended vacuum level needed to remove moisture from the system
is considered to be 27 in. Hg or less. However, many experts recommend
using a vacuum gauge that measures the amount of air remaining in the
system. This type of gauge measures vacuum in microns. A micron is one
millimeter of a meter and there are about 760,000 microns of air at
atmospheric pressure. A vacuum reading of 29.72 in. Hg is about 5,000
microns. Many experts recommend that the micron level be 500 or less for
best results.
This is particularly important when
evacuating a dual-climate control
system where two evaporators are
used and there are long lengths of
refrigerant lines.

Figure 51–9 An air-conditioning vacuum gauge that
reads in microns.
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NONCONDENSIBLE GASES
Refrigerant should be checked for the presence of air, which is 
called a noncondensable gas. This means the air will not 
condense into a liquid when pressurized like refrigerant.
If air is present in the container of refrigerant, it is considered to 
be a contaminate and will reduce the cooling efficiency if 
installed into an air­conditioning system. There are two ways to 
determine if there is air (noncondensable gas) in the refrigerant, 
including:

Use a refrigerant identifier  Most refrigerant identifiers will 
display the amount of air present.
Measure the temperature and pressure of the refrigerant  
Compare the measurement to a temperature/pressure chart.
If the only contaminate is air, it can be purged from the refrigerant. 
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REFRIGERANT RECYCLING
After refrigerant has been recovered, it needs to be recycled for 
further use. Most air­conditioning machines include the ability to 
recycle the refrigerant to the following SAE J1991 specification:

Moisture—Maximum of 15 parts per million (ppm) by weight

Refrigerant oil—Max 4,000 parts per million (ppm) by weight
Noncondensable gases (air)—A maximum of 330 parts per 
million (ppm) by weight

Continued
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RECHARGING A SYSTEM
After the system has been evacuated, it can be recharged with 
refrigerant. Most vehicles have a placard or sticker indicating the 
correct amount of refrigerant to use. 
Figure 51–10 A typical under-hood sticker
identifies the refrigerant and the amount

needed to change the system in kilograms
(0.96 kg is equal to 0.44 pounds).

Figure 51–11 A temperature and humidity
gauge is a useful tool for air-conditioning
work. The higher the relative humidity, the
more difficult it is for the air-conditioning
system to lower the temperature inside the
vehicle.
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The Cadillac Story
When servicing an older Cadillac with an automatic air-conditioning system

(C-68), it was discovered the compressor would not engage. The vehicle
owner stated that a message had been warning him that the system was low
on charge. The technician tightened a slightly loose Schrader valve
and then added about one pound of R-12 to the system, yet the controller
(computer) would not engage the clutch.

The tech then remembered that if a diagnostic trouble code (DTC) has
been set, the computer will not allow the compressor clutch engage.This is
a precaution to prevent compressor damage if the system is low on charge
and not able to transfer lubricating refrigerant oil through the system the
compressor needs for lubrication. The tech disconnected the negative (+)
battery cable, waited several minutes and then reconnected it. After starting
the engine and turning on the A/C controls, the compressor clutch engaged
and the service technician was able to complete charging the system.

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