Heating and Air Conditioning A7 Flashcards

Power and ground at the clutch coil are good, but the compressor clutch will not engage. Which of the following is the MOST LIKELY reason for the problem?

Answer: Incorrect air gap

If the compressor clutch coil receives good power and ground but doesn't engage, the electrical circuit is functional, indicating a mechanical issue. The most likely mechanical problem is an incorrect air gap between the clutch pulley and the clutch plate. If this gap is too wide, the magnetic force generated by the coil is insufficient to pull the clutch plate into contact with the pulley, preventing engagement.

An unknown refrigerant is discovered prior to recovery. The technician should be able to:

Answer: recover it and treat it as contaminated

It is illegal and environmentally irresponsible to discharge any refrigerant into the atmosphere. When an unknown refrigerant is encountered, it cannot be safely recycled as a known type (like R-12 or R-134a) due to the risk of contamination and equipment damage. Therefore, the correct procedure is to recover the unknown refrigerant into a dedicated tank and treat it as contaminated for specialized disposal or reclamation.

The following statements about air conditioning performance test are true, EXCEPT:

Answer: To avoid evaporator odor, you want to operate the AC in RECIRC instead of FRESH

Operating the A/C in RECIRC mode continuously can trap moisture and odors within the cabin and on the evaporator, promoting mold and mildew growth. To help prevent evaporator odor, it's often recommended to periodically use FRESH air mode, especially before turning off the vehicle, to dry out the evaporator and introduce fresh air. Therefore, the statement that RECIRC avoids odor is incorrect.

At low speeds and stop lights, a vehicle's air conditioning performance is reduced, but it cools at highway speeds. Which of the following is the MOST LIKELY cause of this condition?

Answer: A missing fan shroud.

At low speeds or stop lights, the engine's cooling fan and its shroud are crucial for drawing air through the condenser to dissipate heat. A missing fan shroud significantly reduces the fan's efficiency by allowing air to bypass the condenser. This leads to high-side pressure buildup and reduced A/C performance at low speeds, while sufficient natural airflow at highway speeds allows the system to cool effectively.

If the condenser fan wasn't working, what high- and low-side pressure gauge values would a technician find?

Answer: Both high-side high and low-side are high

If the condenser fan is not working, the condenser cannot effectively dissipate heat from the refrigerant. This causes the high-side pressure to become excessively high as the hot refrigerant gas cannot cool and condense. This high pressure then backs up through the system, leading to an abnormally high low-side pressure as well, as the system struggles to cycle the refrigerant.

The compressor clutch isn't going to engage. The technician discovers 14.2V and a good ground at the clutch coil connector during testing. Which of these possibly be the source of the problem?

Answer: An incorrect air gap

When the compressor clutch coil has good power (14.2V) and ground, it indicates that the electrical circuit to the coil is functioning correctly. Therefore, the issue preventing clutch engagement is mechanical. An incorrect air gap between the clutch pulley and the clutch plate is the most likely mechanical cause, as a gap that is too wide will prevent the electromagnetic force from pulling the clutch plate into engagement.

Technician X states that when the condenser airflow is restricted, the pressure is high in both the high and low lines. Technician Y states that when both high and low sides show low pressure, it’s often an indication of low refrigerant. Who is correct?

Answer: Both technicians

Technician X is correct: restricted condenser airflow prevents proper heat dissipation, causing high pressures on both the high and low sides of the A/C system. Technician Y is also correct: abnormally low pressures on both the high and low sides are a classic indication of an insufficient refrigerant charge, meaning there isn't enough refrigerant to properly circulate and build pressure.

A frozen spot is noticed in the center of the condenser. Technician X says a frozen spot on a component or connection indicates a restriction in the system. Technician Y says this is caused Too much freon. Who is correct?

Answer: Technician X

Technician X is correct; a frozen spot on an A/C component or connection, like the condenser, typically indicates a restriction in the system. This restriction causes a sudden pressure drop and corresponding temperature drop at that point, leading to ice formation. Technician Y is incorrect; an overcharge of refrigerant would generally lead to excessively high pressures throughout the system, not a localized frozen spot.

Which of the following factors is most likely to cause a car to overheat?

Answer: Clogged radiator

The radiator's primary function is to transfer heat from the engine's coolant to the ambient air. A clogged radiator, whether internally by deposits or externally by debris blocking its fins, severely impedes this heat exchange process. This reduction in cooling efficiency causes the engine coolant temperature to rise excessively, leading directly to engine overheating.

Technician X says that evacuating an A/C system will remove air and moisture from the system. Technician Y says that evacuating an A/C system will remove dirt particles from the system. Who is right?

Answer: X only

Technician X is correct: evacuating an A/C system uses a vacuum pump to remove air and moisture (as water vapor) from the system. This is crucial to prevent corrosion and ensure efficient cooling. Technician Y is incorrect; evacuation removes gases and vapors but does not remove solid dirt particles; flushing or component replacement is needed for that.

What is the approximate measurement of the A/C compressor high-pressure that release valve discharges refrigerant?

Answer: 475 psi (3,275 kPa)

A/C compressor high-pressure release valves are safety devices designed to prevent system damage by discharging refrigerant if pressure becomes dangerously high. For most automotive R-134a systems, this relief pressure is typically set around 450-500 psi. A measurement of 475 psi falls within this common range, indicating the point at which the system is designed to vent to prevent catastrophic failure.

Two technicians are discussing electric cooling fans and air conditioning performance. Technician X says electric fans regulate refrigerant temperatures more precisely than belt driven fans do. Technician Y says electric cooling fans are controlled by control modules that use temperature and pressure actuated sensors and switches. Who is correct?

Answer: Both technicians

Electric cooling fans offer precise control over refrigerant and engine coolant temperatures because they are directly managed by the vehicle's control module. This module utilizes various temperature and pressure sensors to adjust fan speed, allowing for more accurate and efficient thermal regulation than traditional belt-driven fans. Therefore, both technicians are correct in their understanding of electric fan operation and control.

Technician X says a misadjusted temperature door could cause a poor heat complaint. Technician Y says a defective resistor trio can cause a no high blower condition. Who is right?

Answer: X only

A misadjusted temperature door, also known as a blend door, directly controls the mix of hot and cold air entering the cabin. If it's stuck or mispositioned towards the cold air side, it will prevent adequate heat from reaching the cabin, causing a poor heat complaint. A defective resistor trio, however, typically affects the lower blower motor speeds, not the high speed, which often bypasses the resistor.

The refrigerant should be added to the following to charge an A/C system while it is running:

Answer: the low side only

When charging an A/C system while it is running, refrigerant must always be added to the low-pressure side. This ensures that the refrigerant enters the compressor as a vapor, preventing liquid slugging which can cause severe damage to the compressor. Adding liquid refrigerant to the high side or when the system is off can be dangerous and damaging.

All of these statements regarding A/C-heater control panel service are true, except:

Answer: You must discharge the refrigeration system before the A/C control panel removal.

The A/C control panel is an electrical component located in the vehicle's dashboard and is not physically connected to the refrigerant lines of the air conditioning system. Therefore, discharging the refrigeration system is completely unnecessary when removing or servicing the control panel. Disconnecting the battery and waiting for airbag systems to de-energize are crucial safety steps for electrical work in the dash, and self-diagnostics can indeed identify control panel issues.

In high-demand scenarios, an air conditioning system with a variable displacement compressor performs poorly. ALL OF THESE ARE POSSIBLE CAUSES, WITH THE EXCEPTION OF:

Answer: A faulty low pressure switch.

A variable displacement compressor adjusts its output based on demand. If it performs poorly in high-demand scenarios, it suggests insufficient cooling capacity. A weak compressor, a faulty control valve (which regulates displacement), or a low refrigerant charge would all directly lead to reduced cooling. A faulty low-pressure switch, however, typically prevents the compressor from engaging at all to protect the system, rather than causing poor performance during operation.

The heater blows out only cold air at operating temperature. Technician X says a stuck closed thermostat could be the cause. Technician Y says the cooling system could be low on coolant. Who is right?

Answer: Y only

If the heater blows only cold air despite the engine being at operating temperature, it indicates that hot coolant is not circulating through the heater core. A common cause for this is a low coolant level in the cooling system, which can create air pockets that prevent coolant flow to the heater core. A stuck-closed thermostat would prevent the engine from reaching operating temperature in the first place, which contradicts the problem description.

The low pressure gauge reads 5 psi and the high pressure gauge reads 105 psi with the A/C system operating at an ambient (outside) temperature of 85° F. What do these numbers imply?

Answer: Low refrigerant level

Low pressure (5 psi) on the low side and relatively low pressure (105 psi) on the high side, especially at an ambient temperature of 85°F, are classic symptoms of a low refrigerant charge. A properly charged system at this temperature would typically show higher pressures on both sides (e.g., 30-45 psi low, 180-250 psi high). Insufficient refrigerant means less heat transfer, resulting in reduced pressures throughout the system.

With the temperature selector in the cool position, incoming air is heated in the vent position. What could be the issue?

Answer: Air blend door is stuck.

The air blend door, also known as the temperature door, controls the mixture of hot air from the heater core and cold air from the evaporator. If the temperature selector is set to cool but the incoming air is heated, it means the blend door is stuck in a position that allows hot air to enter the cabin, overriding the desired cool setting. Other options relate to cooling system issues or a clogged heater core, which would not cause heated air when cool is selected.

Technician X says the clutch relay protects the control head from the clutch circuit's high current. Technician Y says open clutch relay windings result in compressor clutch engagement at all times. Who is correct?

Answer: Technician X

The compressor clutch relay acts as a protective switch, allowing a low-current signal from the control head to activate the higher-current circuit required to engage the compressor clutch. This prevents high amperage from damaging the sensitive control head. An open clutch relay winding would interrupt the circuit, preventing the clutch from engaging at all, not causing it to engage continuously.