Evacuate and charge A/C system; add refrigerant oil as required.
Lesson Plan for
AUT 188-189/AUT 293
Automotive Service Technology Section D/Automotive Special Problems
Course HS Title: / Automobile Service Technology/Special Problems / Program:KCTCS Courses included in HS Title: (Lesson is prepared for course highlighted.)
KCTCS Course No. / KCTCS Course Title
Introduction/Context / This lesson will instruct the student on how to evacuate and charge A/C system, and add refrigerant oil as required. Knowledge of these techniques and the skills required to correct problems associated with this task are necessary for a student to acquire if they wish to compete for high paying, high skilled jobs in an Automotive Repair Facility. Entry level technicians need to be able to perform this task to 100% accuracy. Incorrectly performing this task can lead to an automobile accident or create customer satisfaction issues.
Prepared By / School / Date:
Grade Level / No. Students / No.IEP's: / Lesson Length:
Task
Evacuate and charge A/C system; add refrigerant oil as required.
No. / Objective
1 / Given the proper tools and instruction, the student will be able to evacuate and charge A/C system, add refrigerant oil as required, and pass a written test covering the task with 100% accuracy.
Connections:
Skills Standards:OH 001
OH 002
OH 003
OD 002
OD 003
OD 005
Common Core Technical Standards:
TD-SYS-2
New Common Core Standards:
RST 11-12.2
RST 11-12 3
INSTRUCTIONAL MATERIALS/TECHNOLOGY
Teacher Designed Materials and Other Handouts
Textbooks and Workbooks
Chris Johanson / Auto Heating and Air Conditioning / 2009 / Goodheart Wilcox / 262-263
Mark Schnubel / Automotive Heating and Air Conditioning Shop Manual / Fourth / Delmar / 206-208
Web Addresses
Today's Class / Melior / www.todaysclass.com
Equipment
As Needed / Gauges (Manifold Gauge Set, R-12 and R-134A) / Various
As Needed / Refrigerant Charging (R-12 & R-134) / Various
As Needed / Vacuum Pump/Evacuation Gear / Various
Content/Presentation/Demonstration Outline
Tell students that to begin the evacuation, they should connect the manifold and gauge set low- and high-side service hoses to the A/C system. Inform students to make sure that the high- and low-side manifold hand valves are in the closed position and both gauges read zero or less. Next, tell students to remove the protective caps from the inlet and exhaust of the vacuum pump, connect the center manifold service hose to the inlet of the vacuum pump, and then open the shut-off valve of the three service hoses.
Instruct students to connect the power cord of the vacuum pump to an approved power source, and then turn on the vacuum pump. Tell students to open the low-side manifold hand valve and observe the low-side gauge needle. The needle should be immediately pulled down to indicate a slight vacuum. After about 5 minutes, inform students that the low-side gauge should indicate 20 in. Hg (33.8 kPa absolute) or less. The high-side gauge needle should be slightly below the zero index of the gauge.
Let them know that if the high-side needle does not drop below zero, unless restricted by a stop, a blockage in the system is indicated. If the system is blocked, tell them to discontinue the evacuation, and repair or remove the obstruction. If the system is clear, instruct them to continue the evacuation. Tell students to operate the pump for another 15 minutes and observe the gauges. The system should be at a vacuum of 24—26 in. Hg (26.3—13.5 kPa absolute). If it is not, close the low-side hand valve.
Instruct students to observe the compound (low- side) gauge. If the needle rises, indicating a loss of vacuum, there is a leak that must be repaired before the evacuation is continued. If no leak is evident, tell them to continue the evacuation. Have them reopen the low-side manifold hand valve, and open the high-side manifold hand valve.
Tell students to allow the vacuum pump to operate for a minimum of 30 minutes, longer if time permits. After pump-down, inform them to close the high- and low-side manifold hand valves, turn off the vacuum pump and close the service hose shut-off valves, turn off the vacuum pump valve, if equipped, and then disconnect the manifold service hose from the vacuum pump. Remind them to replace the protective caps, if any.
Explain to students that after system repairs are made, the system must be refilled with the proper amount of refrigerant. Before recharging, tell them to make sure the system has the proper amount of oil, and has been evacuated and thoroughly checked for leaks. They should then determine the proper amount of refrigerant before starting the recharging procedure. Let them know that amounts vary from 1.5 pounds (3.3 kg) on a small car to as much as 8 pounds (17.6 kg) on a large vehicle with rear air conditioning. Also make sure you know for certain what type of refrigerant should be used.
Tell students that once the system has been evacuated, to not release the vacuum before charging. Allow the vacuum to draw in the refrigerant. To charge the system using a Recharging with Refrigerant Service Center, tell students to turn the master switch to the ON position, and then attach the hose assemblies to the refrigeration system. Tell them to be sure the shutoff valves are in the closed position. Once connections are made, instruct them to open both shutoff valves.
Tell them to set the refrigerant service center controls to the proper amount of refrigerant. Without starting the engine, instruct them to push the refrigerant service center charge button. They should allow the service center to charge the system with the proper amount of refrigerant. Next, they should then start the engine and HVAC system and set the blower speed to high. Tell them to wait about five minutes for pressures and temperatures to stabilize. Have them place a temperature gauge in the vent closest to the evaporator to check outlet temperature. Instruct them to observe the gauges to ensure the high and low side pressures are correct, and to monitor outlet temperature and other operating conditions to ensure the refrigeration system is operating properly.
To charge using a Charging with Gauge Manifold, tell students to make sure the manifold hand valves are closed and attach the hoses to the appropriate service fittings. Next they should attach the center gauge manifold hose to the refrigerant container to be used. Inform them to purge air from the hoses if necessary. Once all hoses are connected and purged, they should open both gauge manifold valves, which will allow refrigerant to enter both sides of the system with the engine off.
Instruct students that once pressures have stabilized, close both the high and low side valves and start the engine. Have them turn the HVAC system to maximum cooling and set the blower to its lowest position. Tell students to slowly open the low side valve and add refrigerant to the system. DO NOT OPEN THE HIGH SIDE VALVE. Inform students to closely watch high side pressures as they add refrigerant and be sure to not exceed the specified maximum amount.
If pressures rise over 350 psi (2412 kPa), tell students to stop adding refrigerant and allow pressures to stabilize. If necessary, tell them to spray water on the condenser to lower pressure. Let students know that if high side pressure does not stabilize at less than 350 psi (2412 kPa), some refrigerant must be removed.
Instruct students that once enough refrigerant has been added, set the blower speed to high. Tell them to wait about five minutes for pressures and temperatures to stabilize, and then observe the gauges to ensure the system high and low side pressures are correct. Tell them to ensure the refrigeration system is operating properly, then remove the hoses from the refrigeration system and reinstall the caps on the service ports.
Applications/Practice
Evaluation and feedback Prior to Testing or Lab Work
STUDENT ASSESSMENT:(Assess student progress with performance criteria.)
IMPACT--Reflection/Analysis of Teaching and Learning: (How did students’ progress in relation to the state objectives? Was the instruction successful? Analyze samples of student work particularly that which is unsatisfactory, for the purpose of planning further instruction.)
REFINEMENT--Lesson Extension and Follow-up: (To be filled in as the lesson is modified during initial planning and/or during the teaching learning process.)