ASE T7 Truck HVAC Exam Prep Exam Questions & Answers 2026 (21–30)

Question 1

A truck's A/C system has low high-side pressure and normal low-side pressure. Technician A says this could be caused by a restricted condenser. Technician B says this could be caused by a defective compressor. Who is right?

TheoryPractice · Accepted Answer

Technician B only. A restricted condenser would cause high high-side pressure, not low. A defective compressor that cannot properly compress the refrigerant would result in low high-side pressure while the low-side pressure remains normal.

Question 2

When recovering refrigerant from a medium-duty truck A/C system, what is the MINIMUM amount of refrigerant that must be recovered to be in compliance with EPA regulations?

TheoryPractice · Accepted Answer

90% of the system capacity. EPA regulations require that when servicing mobile A/C equipment, at least 90% of the refrigerant must be recovered if the appliance has its compressor working.

Question 3

When adding refrigerant oil to an A/C system, it's MOST important to use:

TheoryPractice · Accepted Answer

The type specified by the manufacturer. Using the correct type of refrigerant oil as specified by the manufacturer is critical. Different refrigerants require specific oil types, and mixing incompatible oils can damage system components and reduce efficiency.

Question 4

What would cause an A/C system's high-side pressure to be excessively high while the low-side pressure is also higher than normal?

TheoryPractice · Accepted Answer

System overcharge. An overcharged system will have excessive refrigerant, causing both high-side and low-side pressures to be higher than normal.

Question 5

A heavy-duty truck's A/C system uses R-134a and has a sight glass in the liquid line. Bubbles are visible in the sight glass during operation. Technician A says this could indicate a low refrigerant charge. Technician B says this could indicate restrictions in the liquid line. Who is right?

TheoryPractice · Accepted Answer

Technician A only. Bubbles in the sight glass typically indicate a low refrigerant charge as the system doesn't have enough liquid refrigerant to completely fill the liquid line. Restrictions would more likely cause high-side pressure increases rather than bubbles.

Question 6

The MOST accurate method to charge an R-134a system in a medium-duty truck is by:

TheoryPractice · Accepted Answer

Weight. Weight is the most accurate method to charge an R-134a system as it ensures the exact specified amount is added regardless of temperature conditions or system state.

Question 7

Before performing a leak test on an A/C system, which of these should be verified first?

TheoryPractice · Accepted Answer

That the system has adequate refrigerant charge. The system must have sufficient refrigerant charge to create enough pressure for an effective leak test. Without adequate pressure, leaks might not be detectable.

Question 8

When using a refrigerant identifier, a sample shows that a truck's A/C system contains a mixture of R-134a and R-12. The CORRECT course of action is to:

TheoryPractice · Accepted Answer

Recover the entire charge into a separate cylinder for contaminated refrigerant. When a system contains mixed refrigerants, the entire charge must be recovered into a separate recovery cylinder designated for contaminated refrigerant. Mixed refrigerants cannot be reused and must be properly disposed of according to regulations.

Question 9

When charging an A/C system on a heavy-duty truck, why is it important to verify that the condenser is clean and unobstructed?

TheoryPractice · Accepted Answer

To prevent abnormally high high-side pressures during charging. A dirty or obstructed condenser reduces heat transfer efficiency, which can cause abnormally high high-side pressures during charging. This might lead to an incorrect diagnosis of system condition or improper charge amount.

Question 10

When inspecting an A/C compressor belt on a Class 8 truck, what is the MINIMUM acceptable belt condition?

TheoryPractice · Accepted Answer

No cracks deeper than 50% of the belt thickness. An A/C compressor belt should have no cracks deeper than 50% of the belt thickness. Deeper cracks indicate significant wear and increase the risk of belt failure during operation.

ASE T7 Truck HVAC Exam Prep Exam Questions & Answers 2026 (21–30)

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