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Lexus RX300 Evaporator and Heater Core Replacement (With Videos)

Hardlymoving writes about do-it-yourself automobile maintenance on various makes and models.

My partner, who takes and edits all my videos, had an AC problem with the Lexus RX 300 he purchased a few years back. There was no cold air coming out of his vents and the AC compressor clutch wouldn't engage.

I did a quick freon compression check and found there was virtually no pressure. We looked around the engine compartment for any tell-tale signs of leakage (compressor oil stains) but found nothing. I injected some UV dye along with enough freon to get the compressor to engage. It turned out to be a very slow leak. He discovered it a few days later when he noticed an odor of freon and compressor oil inside his car.

I was convinced the leak was coming from the evaporator, even though the condensation vent tube showed no signs of UV dye mixed in with the water droplets. Certain that my conclusion was correct, he agreed to have the evaporator replaced. Since the cost of a new heater core and expansion valve was nominal (considering all the work involved in getting to the evaporator), we decided to replace those parts as well.

It took me around eight hours to complete the replacement. For someone who had never performed this type of repair, I would estimate around fourteen hours. No special tools are required to complete this repair, just a lot of patience and perseverance because you have to deal with so many parts and connections to get to the compressor.

How to Stay Organized

This is around the sixth evaporator replacement job I have done in the last couple of years. I used to turn this work down until the customers were begging me to do it for them. Don't know if they loved me, loved what I charge, or both. All I can say is that it gets easier to do the job regardless of the make or model of the vehicle. All cars are put together with the same basic layout with slight differences. The heater and evaporator core replacement in this article was performed with no external sources or instructions; just my past experience. Just follow your repair game plan and deviate very little from it.

The plan is very simple:

After each component or part has been removed, keep the parts in the order they were removed with their respective fasteners (screws, bolts, clips, etc.). If uncertain remembering how a part fits back in during re-assembly, take photos you can refer back to during removal or disassembly.

If you don't feel comfortable evacuating and recharging the system after the core(s) have been replaced, you can bring your car to a shop that has an auto evac and charge machine.

Tools You Will Need

Quality hard plastic panel removal tools (see photo below) should be used to removed various pressed-in plastic facial parts that are held in place with alligator clips. Using metal pry tools may damage or break these parts. As a general rule, if you pull too hard and the thing you are pulling on won't come off, something additional needs to be detached. If you keep pulling under these circumstances, something will break or bend.

Dashboard Pry Tools

Dashboard Pry Tools

The below instructions show you step-by-step how to get to and replace the heater and evaporator cores on a Lexus RX 300. The videos have been segmented allowing you to take breaks between tasks with quick reference points to restart where you last were.

I. Front Seat and Center Arm Rest Console Removal

We need to remove the front seats to maneuver around the dash area to remove the various dash components. After the seats are out of the way, the center armrest console is removed to open up the entire area. The door sill plates on both the left and right side are removed in order to remove the kick plates.

The video below will show you how I did it.

II. Glove Box, Door Trim Molding, Dash Pillars, Lower Dash Panels, Center Dash Control Switch Plates Removal

Continuing with our path getting to the evaporator, the glove box, door trim molding, dash pillars, and lower dash panels must be removed.

  • The glove box is held in place with a few Phillips screws,
  • The door trim molding must be pulled away to allow the removal of the dash pillars.
  • The dash pillars must be removed to allow the dash to pull out.
  • The driver's side lower dash panel must be removed to allow various electrical connectors to be detached. The hood latch cable must be detached from the lower dash panel.
  • To the left and right of the steering wheel are control switch and ignition panels that must be removed with their electrical fitting detached.

The video below will show you how I did it.

III. Instrument Cluster, Shift Console Bezel, Shift Console Cover, Shift Assembly and Radio Removal

  • A black bezel covers the outside perimeter of the instrument cluster and is held in place with two top screws and alligator clips. After the screws have been removed, the bezel can be pulled out. This will expose the four screws that hold the instrument cluster. After removing the screws, the cluster can be pulled and rotated to expose the electrical connectors that can be disconnected.
  • The shift console bezel (wood grain color) can be pried off of their alligator clips exposing all the electrical connectors. Detach the connectors.
  • The shift console cover is screwed and bolted in place. Remove these screws and bolts. At the base of the cover are attached kick plates held by plastic fasteners that must be removed.
  • The transmission shift assembly is held in place with four nuts. Remove these nuts, and detach the shift cable attachment and the electrical fittings. The assembly can now be removed.
  • The radio assembly is held in place with four nuts. Remove these nuts, pull out the assembly and disconnect all the electrical connectors.

The video below will show you how I did it.

IV. Steering Column Cover, Glove Box Vertical Supports and CD Player Removal

  • Turning the steering wheel 90 degrees to the left and right will expose the lower steering column cover screws. Remove these screws and the single screw on the bottom of the cover. Both the upper and lower covers can now be removed. Detach the steering wheel's electrical connections.
  • Remove the two vertical supports for the glove box.
  • Remove the CD player's mounting nuts and remove the player.

The video below will show you how I did it.

V. Unbolt All Connections to the Dash Cross Member and remove the Dash

  • Remove the two nuts that hold the passenger-side airbag to the dash cross member.
  • Unbolt the fuse box from the cross member
  • Unbolt the dash hangers by the steering column from the cross member.
  • Detach all electrical connectors and wire fasteners from the dash.
  • Drop the steering column by removing the four nuts that hold the column to the cross member.
  • Pull the dash out of the car. I recommend getting a second pair of hands to help.

The video below will show you how I did it.

VI. Dash Cross Member Removal

  • Remove the left and right air ducts by the side of the two cross-member vertical supports.
  • Unbolt and remove the two cross-member vertical supports.
  • If not already done, unbolt the fuse box from the cross member.
  • Unbolt the cross member from the front chassis of the car.
  • On the right side of the air box, unbolt the electrical control boxes from the cross member and detach the electrical connectors.

The video below will show you how I did it.

VII. Detaching the Heater Hose and AC Supply and Return Lines in the Engine Compartment

Before the heater and evaporator core housing can be removed, the heater and evaporator core supply and return hoses and pressure fittings must be disconnected from inside the engine compartment. These connections are on the firewall and cannot be accessed unless the windshield wiper motor cowling and the air intake hose assembly are removed.

  • Remove the air filter upper hose assembly and detach it from the throttle body.
  • Remove the windshield wipers, followed by the rubber weather guard, plastic upper cowling cover, wiper motor assembly, and the cowling.
  • Pinch and shift the heater hose clamps away from the heater core fittings. Use hose pliers to twist the hoses off.
  • Unbolt the single bolt that holds the supply and return lines to the expansion valve. Wiggle the connection off.

The video below will show you how I did it.

VIII. Heater and Evaporator (HVAC) Housing Removal

  • Remove the plastic duct fittings on the HVAC housing. The black plastic duct on top and the duct on the left side, the white right side duct, and the front duct connected by four screws.
  • Disconnect all electrical connectors, plastic ducts, and brackets between the blower motor housing and the HVAC housing.
  • Unbolt the two top HVAC housing bolts and the bottom right bolt. Pull out the condensation tube from the floor. The housing can now be pulled out.

The video below will show you how I did it.

IX. Heater and Evaporator Core Replacement

The HVAC housing consists of two halves joined together by sheet metal-type screws. Within the housing are three hinged air direction doors connected by the two compartments:

  1. the fresh air or recirculate door
  2. the air mix or blend door
  3. the air direction door: up, down, middle or combined

The doors are actuated by servos or actuator motors controlled by the HVAC dash head unit that relies on input preferences from the driver.

To remove the evaporator, you have to open the HVAC housing by separating the two halves. The process for replacing the heater and evaporator core is as follows:

  • Detach the two metal heater core tube clamps.
  • Pull out the heater core.
  • Remove the screws and clips that hold the two halves together.
  • Remove the dust screens on the up side portion of the housing.
  • Separate the halves.
  • Detach the A/C coupler (that holds the expansion valve) from the evaporator.
  • Pull out the evaporator.
  • Transfer the plastic cover from the old evaporator to the new evaporator.
  • Mount the new evaporator into the housing halve then join the 2 halves. Ensure the door hinge pins are in their hinge holes. You can use any thin tip screwdriver to assist with the alignment.
  • Re-install the removed clips and screws to keep the housing halves together.
  • Install the heater core and secure in place with the two metal tube clamps.
  • Re-install the dust screens (now or later). Aluminum duct tape works well in keeping the screens from moving. Afterward, apply foam insulation strips on the borders of the dust screens.

The video below will show you how I did it.

X. Replacing and Insulating the Expansion Valve

  • Remove the two long bolts that hold the expansion valve to the AC coupler. Wiggle off the expansion valve and replace with the new expansion valve. Replace the old O-rings with new ones and lubricate them with compressor oil. Re-install the two long bolts.
  • Connect the AC coupler with the new expansion valve to the new evaporator connection ports.
  • Using HVAC foam insulation wrap (you can find it in a hardware store), wrap the insulator around the AC coupler tubes.
  • Install new O-rings on the engine compartment AC lines that will connect later on with the expansion valve.

The video below will show you how I did it.

XI. HVAC Housing Re-installation

The HVAC housing can be re-installed in the same manner it was removed. Align the air input port of the housing with the blower motor housing, and then push the supply and return hoses and pipes of the heater and evaporator core through the firewall. Once connected, the housing can be bolted in place. Don't forget to connect the condensation vent tube to the housing and push the vent tube through the floor opening.

The video below will show you how I did it.

XII. Heater Hose and AC Connection and AC Vacuum Test

Back inside the engine compartment, re-connect the heater hoses to the heater core tubes and the AC lines to the expansion valve.

Re-install the wiper motor cowling, wiper assembly, plastic cowling cover, rubber weather stripping, and the wiper arms.

Before putting everything back together, I tested the new evaporator by performing a vacuum (evacuation) test. The high and low side service port valves were first replaced followed by a vacuum hold test. This involved pulling a vacuum and seeing if my low-pressure gauge was moving back to zero after I closed off the lower pressure gauge. If the needle moves much in the first minute or so, there's still a leak somewhere in the system. In my case, there were no leaks.

The video below will show you how I did it.

Re-Assembly of the Interior Components

If you set down all of the removed interior components in the order they were removed, then there should be no problem installing them back in reverse order. The positioning and connection of electrical connectors can cause some confusion but if you have been taking pictures as you were detaching them, reference the pictures if or when you get confused.

You can refer to my articles on either the Toyota Sienna or Honda Pilot AC compressor replacement for instructions on evacuation and recharge of the AC system.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2018 hardlymoving