Automotive Service Technology Section C/Automotive Special Problems
Course HS Title:
Automobile Service Technology/Special Problems
KCTCS Courses included in HS Title: (Lesson is prepared for course highlighted.)
KCTCS Course No.
KCTCS Course Title
This lesson will instruct the student on how to performance test A/C system, and identify problems. 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.
Performance test A/C system; identify problems.
Given the proper tools and instruction, the student will be able to performance test A/C system; identify problems, and pass a written test covering the task with 100% accuracy.
Instruct students that the performance test checks the refrigeration and heating system components for proper pressures and temperatures. Some of the test procedures do not apply to every system. Tell students to always make sure they obtain and use the manufacturer's procedures and specifications for function and performance tests.
Instruct students that to make the performance test, shut off the engine, make sure the transmission is in Park or Neutral, and set the parking brake. Attach gauges or a refrigerant service center. Tell students to be sure the high and low side hoses are attached properly. Once the gauges are attached, tell them to check static (engine not running) pressure. Explain to students that a normally charged system will have 70-125 PSI (482-861 kPa) when it has been inactive for about one hour. If the gauges show low or no pressure in the system, let them know that they can be sure there is a leak somewhere. Tell students to be sure the hoses do not contact any moving parts.
Inform students to install a temperature gauge in the vent nearest the evaporator, then start the engine and set it to run at approximately 1500 to 2000 RPM (this will vary by manufacturer). Tell them to then turn the HVAC control panel settings to the maximum cooling position and set the temperature switch to the maximum cold position, then turn the blower speed switch to the high position and open the front windows.
Instruct students to check the compressor clutch to make sure it is engaged. If the clutch does not engage, tell students to shut off the HVAC system and engine and check the clutch, relay, switches, and wiring.
If the compressor clutch engages, teach students to allow the refrigeration system to operate for about five minutes to stabilize the gauge readings. Let them know to monitor the cooling system gauge or light to ensure the engine does not overheat. Tell them to observe the fan clutch or fan motor) and ensure they are operating and moving air through the condenser and radiator.
STUDENT CAUTION: If the cooling system fans are not operating, or if the high side pressure exceeds 325 psi (2467 kPa), stop the performance test immediately and determine the cause.
Inform students that if the system is operating normally, high side pressure should be between 150 and 300 PSI (1034 to 2067 kPa) on a R-134a system. Explain that R-12 high pressures are usually somewhat lower, about 250 PSI (1723 kPa). Low side pressures should be between 30 and 40 PSI (208 and 276 kPa),
Inform students that the following information shows the possible causes for test results being out of specifications. Outlet air temperature from the center dashboard vent is higher than normal/ Air mix door is out of adjustment. Outlet air temperature from the corner dashboard vents varies by more than 10 OF/ Air mix door is out of adjustment. Refrigerant system low-side pressure is too low, and the outlet air temperature from the right corner dashboard vent is at least 10 of cooler than the left corner dashboard vent/Low refrigerant charge or restricted refrigerant flow through the evaporator. Pressure on the high side of the refrigerant system is too high/ Restricted airflow through the condenser, the condenser/radiator fan is inoperative, or there is restricted refrigerant flow through the system. Pressure on the high side of the refrigerant system is too low/System is low on refrigerant charge.
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Evaluation and feedback Prior to Testing or Lab Work
Objective 1. / Formative assessment / Instructor will observe students as they practice the procedure to assure correct procedure and safety practices are being followed. A checklist will be utilized to chart student progress on the task. Questioning techniques will be utilized as necessary to demonstrate student comprehension / Adaptations and/or accommodations for special needs students will be added if required.
STUDENT ASSESSMENT: (Assess student progress with performance criteria.)
Objective 1 / Summative assessment / written test questions on stated objective / adaptation and / or accommodations for special needs students will be added if required
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.)