jgtodd42

2001 RX300. A/C works fine, but heater won't put out any heat...just cool air. Any ideas on cause?

blueridge

May be the servo that controls the temp door. Follow this procedure to check the code. More than likely you will see 31, 33, and 41.

I pulled out the glove compartment and the small trim panel near the passenger's left foot and was able to see if the servos were moving with temp/vent control **** inputs. I had both servos failed, I removed the servos, cleaned the contacts, greased the tracks.

You have two servos, upper and lower. The upper controls the door position for vents selection (defrost, feet, upper, both, etc) and the lower servo controls the door for temperature.



SELF-DIAGNOSTICS
An Electronic Control Unit (ECU) within A/C-heater control
panel monitors system circuits and stores trouble codes in memory if
problems are detected. All codes, except Codes 22 and 23, are stored
in memory. Malfunction is current if Code 22 or 23 is displayed. To
retrieve stored codes, see RETRIEVING CODES. Codes are displayed at
temperature display. See Fig. 2.
RETRIEVING CODES
1) Simultaneously press and hold AUTO and recirculated air
switches. See Fig. 2. Turn ignition on. All indicators will flash 4
times, at one-second intervals. Tone will sound when indicators flash.
2) A/C system will enter self-diagnostic mode. To end
indicator check, press and release OFF switch. Read codes at
temperature display.
3) If trouble code is displayed, proceed to appropriate
trouble shooting procedure. See DIAGNOSTIC CODE IDENTIFICATION table.
Codes are displayed in ascending order. To slow rate at which codes
are displayed, press fresh air button to change display to step
operation. Each time fresh air button is pressed, display changes by
one step.
4) If tone sounds as code is displayed, problem currently
exists. If tone does not sound as code is displayed, problem occurred
in past and does not presently exist.
Code Diagnosis
00 ...............Normal
11 (1) ..........In-Vehicle Temperature Sensor Circuit
12 (2) ..........Ambient Temperature Sensor Circuit
13 ...............Evaporator Temperature Sensor Circuit
14 ...............Coolant Temperature Sensor Circuit
21 (3) ..........Solar Sensor Circuit
22 (4) ..........Compressor Lock Sensor Circuit
23 (4) ..........Pressure Switch Circuit
31 ...............Air Mix Door Position Sensor Circuit
32 ...............Air Inlet Door Position Sensor Circuit
33 ...............Air Outlet Door Position Sensor Circuit
41 ...............Air Mix Door Servomotor Circuit
42 ...............Air Inlet Door Servomotor Circuit
43 ...............Air Outlet Door Servomotor Circuit
(1) - If in-vehicle temperature is -4  F (-20  C) or less,
Code 11 may set even though system is normal.
(2) - If outside air temperature is -58  F (-50  C) or less,
Code 12 may occur set though system is normal.
(3) - If testing is done in a dark area, Code 21 may set
even though system is normal. Shine a light at solar
sensor and recheck codes.
(4) - Malfunction is current. Code is not stored in memory.

ACTUATOR CHECK
1) Perform step 1) of RETRIEVING CODES. When system enters
self-diagnostic mode, press recirculated air button. Each mode door,
motor, and relay will operate at one-second intervals. Press fresh air
button to display codes one at a time, and perform step-by-step
actuator check.
2) Check airflow and temperature by hand. Tone will sound
each time display code changes. Each display code is associated with a
system operating condition. Press OFF button to
cancel actuator check mode.

salimshah

Diy diagnostic sticky candidate.

Salim

jgtodd42

Ran self-diagnosis per instructions. Got codes 21, 31 and 41. Then tested each mode one at a time. Every vent and fan speed seems to be OK. Puts out cool or cold, but air doesn't heat. Other ideas?

blueridge

Pull the glove box out, there are two screws on top and two bolts on the bottom. You will be able to see the servos then. They are black boxes with white arms.

The lower one is the one for heat, that is the one that in inop. Turn on the system and move the vent selector ****, you will see the upper servo move. Adjust the temp and the lower one should move, if not then that is your problem. It's a common problem because the servo is right next to the lines going to the heater core. The lines are a pair and they are stainless looking. They get very hot so be careful if your RX has been running for a while.

You can disconnect the wires going to it and clean the contacts. I wound up removing it, opening up the servo (you will break the ears but no biggy) and lubing everything. Works good now!