1. Heating and Air-Conditioning Service
Chapter 36

2. Objectives
Locate obvious problems in heating and air-conditioning systems with a visual inspection
Test air conditioner efficiency and pressures
Locate leaks in the refrigeration system
Diagnose and repair problem components
Evacuate and recharge a refrigeration system in a safe and legal manner

3. Heater Service
Complaints are usually related to coolant leaks or inappropriate temperatures for the season
Heater flow can be checked by feeling hoses at inlet and outlet to heater core
Heater core replacement
Leaking heater core replaced
Heater housing must be removed

4. Air-Conditioning Service
Challenging and rewarding specialty area
Technicians must be licensed to service all air- conditioning systems
Air-conditioning safety
Always the highest priority
Be sure to use the correct refrigerant

5. Air-Conditioning System Service and Diagnosis
Visual inspection considerations
Coolant level
Condenser
Fans
Compressor drive belt
Refrigerant hoses
Wiring and hoses

6. System Performance Test
Includes:
Locating specifications
Identifying the refrigerant type
Connecting pressure gauges
Measuring outlet duct temperatures
Refrigerant identifier
Determines the refrigerant type is correct
Testing air-conditioning efficiency
Set control to maximum cool
Set blower to high

7. Pressure Testing Pressure gauge set Service valves
Used to measure pressures in the system
Service valves
Discharge service valve is on the output side of the compressor on the high side
Suction service valve on the inlet to the compressor on the low side
Connecting the gauges
Use quick-disconnect couplings on the refrigerant machine

9. Static Pressure Reading
Pressure reading in the system when it is not operating
High- and low-side pressure will be equal when there is no refrigerant movement
Pressure is equal when in a confined area

10. Static Pressure Reading (cont’d.)
Reading system pressure
When you start the engine and turn on the air- conditioning, the low side pressure will drop
Inspect the sight glass if the system has one
System operating pressure
Humidity affects system pressure
Pressure test results
Can point you to possible problems

11. Static Pressure Reading (cont’d.)
System operation quick check
Feel the temperature
Check for hot and cold
Air distribution system inspection
Low side is cool but system is not cooling
Problem could be with air door or panel controls
Air discharge temperatures
Most deal with temperatures on Fahrenheit scale
Air-conditioning system noises
Some are normal and some indicate problems

12. Diagnosing HVAC Electronic Problems
Most automatic temperature control systems have self-diagnostic capability
HVAC module controls compressor clutch circuit
Electronic control problems with an HVAC system are often due to an electromechanical cause
Be certain all mechanical parts of the system are operating correctly

13. Air Distribution System Diagnosis
Air distribution system problems
Often the cause of customer complaints
Automatic temperature control system diagnosis
Automatic temperature control (ATC) systems differ between manufacturers
Electric motor actuators
Manual and automatic electric air-conditioning system actuators are similar
Door problems
Air door and blend door

14. Air Distribution System Diagnosis (cont’d.)
Mode door
Directs air in response to the commanded temperature from the control head
Fresh air setting
More efficient when temperature inside the vehicle is above outside ambient air
Recirculating setting
Allows some fresh air to enter
Cabin air filters
Cleans circulated air

15. Air Distribution System Diagnosis (cont’d.)
Ion generators
Used to purify air
Blower and blower control module problems
Heat generated between brushes can shorten motor life
Replacing a blower
Be aware that the direction of some motors can be reversed
Diagnosing an inoperable blower
Most likely causes electrical wiring or controls

16. Air Distribution System Diagnosis (cont’d.)
Blower power module problems
Do an amp draw test on the blower motor
Restricted airflow
Can be due to a plugged cabin air filter or an oily evaporator that has accumulated dust
Sensor testing
Input sensor should hold tissue and drop it off when it goes off
Ambient sensor problems
Possible culprit when no cold air comes from vents

17. Leak Detection Methods O-rings and seals Soapy water
UV dye leak detection
Colored dye
Electronic leak detection
O-rings and seals
Threaded fittings and block fittings are often sealed with O-rings

18. Common Air-Conditioning Component Problems
Prior to component removal
Capture all of the refrigerant
Accumulator or receiver/dryer service
Receiver/dryer or accumulator
Should be replaced whenever its systems has been leaking, left empty, or left open for a long time

19. Refrigerant Oil
Lubricates compressor, gaskets, seals, and expansion valve
Choosing the right oil
The oil must be compatible with the refrigerant
Be sure to use the correct type and viscosity
In an orifice tube/accumulator system, most of the refrigerant in the evaporator will be liquid

20. Evaporator Problems
Some manufacturers put a layer of foam on the outside of the passenger side of an evaporator
Prevents water from being blown on passengers
Some technicians spray Lysol on the foam if it mildews
If an evaporator leaks, it must be replaced
Usually located within the dashboard
Replacing it can be time consuming

21. Thermal Expansion Valve or Orifice Tube Problems
Orifice tube system cycles the clutch to control refrigerant flow through the system
Expansion valve
When an expansion valve is not working correctly, system pressures will not be as expected
Common problem: failure of the sensing bulb
Orifice tube service
Accumulator should feel cold and sweaty
Orifice tube is easily checked and replaced

22. Compressor Service Compressors are relatively reliable
Usually fail as a result of a leak
Replacing a compressor
Be sure the new one has the correct part number
Refrigerant filters
Can be added
Flushing an air-conditioning system
Aftermarket compressor manufacturers require solvent flushing

23. Compressor Service (cont’d.)
Clutch problems
Check for source voltage
Clutch failures
Several reasons (e.g., excessive air gap)
Clutch replacement
New clutch assemblies are commonly available
Clutch plate is removed first
Compressor shaft seal replacement
Special tools are available

24. Evacuating and Recharging
Two additional hoses attached to center connection on manifold set
Refrigerant supply tank hookup and remote vacuum
Refrigerant identification
Before evacuating refrigerant, be certain it is the same refrigerant as in tank reservoir

25. Vacuuming a System
Vacuuming dries moisture and helps the efficiency of the system
Must have a high-quality vacuum pump to remove most moisture from the system
For best results, try to achieve at least 29.5" of vacuum and always evacuate for at least 20 minutes
Required time for factory evacuations is only 45 seconds
Protect a vacuum pump by changing its oil every ten hours or less

26. Evacuate the System Evacuation and recharging
Done with engine off by connecting center hose to both service ports and opening both valves
Connect the center service hose to vacuum pump
When vacuum pump starts, system pressure drops
Following evacuation close all valves and shut off the pump
Replacing refrigerant oil
Refrigerant charge is 10% low: pressure might be too low to circulate oil

27. Air-Conditioning Service Equipment
Dual pass machine
First recover then recycle
Single pass machine
No need to ever charge with vapor
Machine recovers the refrigerant and recycles it during a 15-minute minimum vacuum cycle

28. Refrigerant Charging
After evacuation process is complete, refill the system with refrigerant
Refrigerant charge amount is critical and each system is different
Evaporator and accumulator temperature tests
Evaporator inlet and outlet temperature test
Accumulator inlet and outlet temperature test
Incorrect refrigerant fill
Pressure gauge readings are not dependable
Scale may not be accurate

29. Refrigerant Charging (cont’d.)
Determine the correct refrigerant amount
Usually found on an under-hood label
Refilling through the low side
Liquid refrigerant entering the low side can damage the compressor
Completing the refill
System should begin to operate normally when the fill level is about a half pound less than full

30. Follow-Up Following air-conditioning system maintenance or repair work
System performance test should be done
Verify success of work

31. Refrigerant Storage Commercial refrigerants
Typically sold in 30 lb containers
Resemble propane bottles
Disposable
Have blow-off protection
Different refrigerants should not be mixed
This will form a new chemical compound
Can cause higher pressures, resulting in damage

32. Recycling and Retrofit
Retrofitting an R-12 system is possible
There are some drawbacks
Manufacturers have kits
Go back ten model years
Items a retrofit might require
Compressor front seal
Large condenser
Desiccant
Extra cooling fan
Hoses and O-rings