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newSchoolWorks.com › VoTechWorks › Transportation › Automotive Technology › Automotive Heating, Ventilation, and Air Conditioning (HVAC) › Lesson 6
TRN-AUTO19-06 · Lesson 6 · 22 clock hours · lab

Condenser, Evaporator, Receiver-Drier, and Expansion Device Service

Objective. Students will replace an orifice tube or thermal expansion valve (TXV) and receiver-drier/accumulator on a training vehicle, using proper flushing and contamination-prevention procedures.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why These Components Matter

The condenser, evaporator, receiver-drier, accumulator, and expansion device are the heart of the refrigerant circuit. When any one of them fails—or when compressor debris contaminates the system—simply swapping the broken part is not enough. Leftover oil sludge, metallic particles, or moisture will destroy a new compressor within hours. This lab teaches you to clean the circuit properly, replace the expansion device and drying unit, and confirm the system performs to specification before returning the vehicle.

System Contamination and Flushing

When a compressor fails internally, it sends metal particles and degraded oil throughout the high- and low-pressure sides of the circuit. The condenser and evaporator act as collection points for this debris. Before installing any new parts, you must flush the evaporator core and the liquid line—the two components that cannot simply be replaced as part of routine repair and that trap the most contamination.

Always recover refrigerant completely with the shop's refrigerant recovery, recycling, and recharge (RRR) machine before opening any fitting. This is both a legal requirement under EPA Section 608 regulations and a safety necessity—liquid refrigerant contacting skin or eyes causes frostbite, and refrigerant vapors displace oxygen in enclosed spaces. Wear safety glasses and insulated gloves throughout.

Use only an approved HVAC flush solvent in a dedicated flush tool; never use brake cleaner, carburetor cleaner, or compressed air alone—they leave residue that contaminates oil or damages seals. Follow the flush tool manufacturer's procedure: typically you inject solvent in the direction opposite to normal refrigerant flow, then blow dry with dry nitrogen. Capture all used flush solvent in the tool's collection bottle and dispose of it according to your shop's hazardous-waste protocol—it is considered a regulated waste in most jurisdictions. Do not flush the compressor, the expansion valve (TXV), the orifice tube, or any component with a built-in filter screen; replace those instead.

Expansion Device Service

Orifice tube (OT): Found in accumulator-style (low-pressure side) systems, the orifice tube is a fixed restriction usually located in the liquid line at the inlet of the evaporator. A dedicated orifice tube removal tool grips the tube's plastic body and pulls it straight out. Inspect the screens for metallic debris—heavy debris confirms compressor failure and the need for a full flush. Install the new OT with the small screen end (inlet) facing the condenser. No torque is required for the tube itself, but any Schrader caps, line fittings, or block-type connectors must be torqued to specification.

Thermal expansion valve (TXV/TEV): Found in receiver-drier systems (high-pressure side drying), the TXV meters refrigerant by sensing evaporator outlet temperature and pressure through a sensing bulb and an internal equalizer port. When replacing a TXV, use a back-up wrench to hold the valve body stationary while you turn the line fitting—failure to do so twists the valve body, damaging the sensing bulb capillary tube or the internal piston. Always replace the O-rings on every fitting. Lubricate O-rings with the correct refrigerant oil for the system: PAG oil for R-134a systems, POE oil for R-1234yf systems. Never mix oil types. Torque all fittings to the vehicle manufacturer's specification found in the service information.

Receiver-Drier and Accumulator Replacement

The receiver-drier (high-side, used with TXV systems) and the accumulator (low-side, used with orifice-tube systems) both contain desiccant that absorbs moisture from the refrigerant. Desiccant is rated for a finite amount of moisture absorption; it must be replaced any time the system is opened to the atmosphere, after a component failure, or whenever service information specifies. Cap all openings immediately after removing the old unit to prevent atmospheric moisture from entering the new one before installation. Add the quantity of refrigerant oil specified in the service information to compensate for oil retained in the old drying unit.

Evacuation and Recharge

After all components are installed and fittings are torqued, connect the RRR machine and pull a deep vacuum—typically 500 microns or lower as verified with a micron gauge—and hold it for a minimum period specified in the service information (commonly 30 minutes). A rising vacuum indicates a leak or remaining moisture; do not proceed until the system holds. Recharge with the exact refrigerant type and weight stamped on the vehicle's underhood label. Never mix refrigerants.

Performance Verification

With the engine running, A/C on maximum, blower on high, and doors open, record the center vent temperature and the high- and low-side pressures. Compare these readings to the temperature-pressure charts and expected values in the service information for the ambient temperature at the time of the test. A properly functioning system should deliver vent temperatures well below ambient. After your instructor inspects for leaks with an electronic leak detector—zero leaks are required to pass—document all torque values, oil added, refrigerant charge weight, and performance readings on your lab worksheet.

Key terms9

Orifice tube (OT)A fixed-diameter metering device in the liquid line that restricts refrigerant flow into the evaporator; used in accumulator-style A/C systems.
Thermal expansion valve (TXV)A variable metering valve that regulates refrigerant flow into the evaporator based on evaporator outlet temperature and pressure, providing precise superheat control.
Receiver-drierA high-side component in TXV systems that stores liquid refrigerant, filters debris, and contains desiccant to absorb system moisture.
AccumulatorA low-side component in orifice-tube systems located at the evaporator outlet; stores excess refrigerant and contains desiccant to remove moisture.
HVAC flush solventAn approved chemical designed to dissolve and carry away contaminated refrigerant oil and debris from internal circuit passages without leaving harmful residue.
PAG oilPolyalkylene glycol synthetic refrigerant oil used in most R-134a A/C systems; not compatible with R-1234yf systems without specific approval.
POE oilPolyol ester synthetic refrigerant oil compatible with R-1234yf and also approved for some R-134a systems; must not be mixed with PAG oil.
Back-up wrenchA second wrench used to hold a component stationary while a fitting is tightened, preventing torque from twisting or damaging the component body or attached capillary tubes.
Micron gaugeAn instrument that measures vacuum in microns of mercury (µmHg); used to verify that system evacuation has reached the depth required to remove moisture before recharging.

Worked examples4

1. The service information states you must add 1.0 oz of PAG oil to a new accumulator to replace oil lost with the old unit. The shop's PAG oil bottle is graduated in milliliters. How many milliliters do you measure out? (Use 1 fluid ounce = 29.574 mL)
  1. Identify the required quantity: 1.0 fluid ounce.
  2. Apply the conversion factor: 1.0 oz × 29.574 mL/oz = 29.574 mL.
  3. Round to the nearest whole milliliter for practical measurement: 30 mL.
Answer: Measure 30 mL (approximately 29.6 mL) of PAG oil to add to the new accumulator.
2. The underhood label specifies a refrigerant charge of 1 lb 4 oz of R-134a. The RRR machine displays charge weight in ounces. What total number of ounces should the machine dispense?
  1. Convert pounds to ounces: 1 lb × 16 oz/lb = 16 oz.
  2. Add the remaining ounces: 16 oz + 4 oz = 20 oz.
  3. Enter 20 oz as the target charge weight on the RRR machine.
Answer: The machine should dispense 20 oz of R-134a.
3. After recharge, the center vent temperature reads 48 °F and ambient temperature is 85 °F. The service information says the expected vent temperature drop below ambient at this condition is at least 35 °F. Does the system meet specification?
  1. Calculate actual temperature drop: 85 °F − 48 °F = 37 °F.
  2. Compare to specification: 37 °F ≥ 35 °F (minimum required).
  3. The actual drop exceeds the minimum, so the system meets specification.
Answer: Yes, a 37 °F drop meets the service specification of at least 35 °F below ambient.
4. A TXV inlet fitting requires 18 ft-lb of torque. Your torque wrench is graduated in in-lb. What reading should the wrench click at?
  1. Convert ft-lb to in-lb: 18 ft-lb × 12 in/ft = 216 in-lb.
  2. Set or watch for the torque wrench to signal at 216 in-lb.
Answer: Torque the fitting until the wrench signals at 216 in-lb.

The math in this lesson2

Learners convert 1 lb 4 oz to ounces, 18 ft-lb to in-lb, and PAG oil volumes.
N-Q.1N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: After refrigerant recovery (using skills from Lesson 3), flush the evaporator and liquid line of a contaminated training circuit using approved HVAC flush solvent following the flush tool manufacturer's procedure; capture and dispose of used flush according to the shop's hazardous-waste protocol. · Replace the orifice tube or TXV on the assigned vehicle using new O-rings lubricated with refrigerant oil appropriate for the refrigerant type; torque fittings to specification using a torque wrench and back-up wrench to prevent component rotation. · Install a new receiver-drier or accumulator, evacuate, and recharge the system; perform a system performance test recording vent temperature and pressures, then compare to the expected values in the service information.
Materials: Assigned training vehicles, HVAC flush tool and solvent, orifice tube removal tool, TXV service kit, receiver-drier/accumulator units, O-ring kit, appropriate refrigerant oil (PAG or POE per application), torque wrench and back-up wrench, RRR machine, service information
Check: Instructor inspects fittings for leaks with electronic leak detector after recharge; zero leaks required. Lab worksheet documents all steps with torque values, oil added, charge weight, and performance readings—80% rubric score required.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

A7 Heating and Air Conditioning
1. Why must technicians use a back-up wrench when torquing a TXV line fitting?
A7 Heating and Air Conditioning
2. An orifice-tube system has failed due to internal compressor damage. After compressor replacement, which additional component must be replaced because it contains desiccant that has absorbed contamination?
A7 Heating and Air Conditioning
3. Which refrigerant oil is specified for use in an R-1234yf A/C system?
A7 Heating and Air Conditioning
4. Before opening any refrigerant fitting during a component replacement, the first required step is to:
A7 Heating and Air Conditioning
5. When flushing a contaminated evaporator core, a technician should flush solvent in which direction?
A7 Heating and Air Conditioning
6. After installing a new receiver-drier and all fittings, the technician pulls a vacuum. The micron gauge reads 480 microns, then rises steadily to 2,500 microns over 10 minutes with the vacuum pump valve closed. This most likely indicates:
A7 Heating and Air Conditioning
7. Used HVAC flush solvent captured during a system flush must be:
A7 Heating and Air Conditioning
8. A technician installs a new orifice tube and notices the small screen is facing toward the evaporator inlet rather than toward the condenser outlet. What is the most likely result if the system is charged and operated?
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