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Heater Control Valve


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I am looking for the heater control valve from a 1992 through 2000, Lexus SC300 or SC400. It is located in the engine bay on the firewall on the passenger side. Lexus wants $400 plus $150 to install. Anyone know of a wrecked 1992 through 2000 SC300 or SC400??

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Try this:

Maybe they can help

Is it the just the valve - you can reverse the vacuum lines and the valve will shut or open depending on what you need. Then disconnect. That is what others have done. They reconnect when they need heat or whatever for the winter. I know it is not fixing the problem but dealing with it and it is cheaper - maybe easier. I'll try to get more info on that.

Where in Chicagoland are you at? I'm from Gurnee originally.

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  • 1 month later...

A bad thermostat perhaps? If the thermostat is a "fail-safe" type then it can stick open i.e. coolant is constantly circulating through the radiator. Is your coolant temp gauge in the normal range? At idle the coolant would warm up providing some heat but once you start driving the temp could drop well below 195F to the point where you don't get much heat from the vents. Anyway, a new thermostat is cheap and it's easy to check if the thermostat is stuck open. Start the engine when it's cold and squeeze the hose that supplies the radiator ... if the thermostat is working properly you shouldn't be able to feel any pressure build up in the hose as you're constricting it.

:)

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I should have mentioned it earlier, but that was the first thing that I replaced. I did it even though the engine warmed up as it should. Alas, it did not work. I checked both hoses on either side of the heater control valve and both are hot. I manually actuated the valve and it still does not blow warm air. At least I've got some time to figure it out. Kee the suggestions coming!!

Marty

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The car never overheats, even when driving from Houton to Chicago non-stop. (it didn't blow heat either). The fluid level is AOK. When I changed the thermostat, I refilled the system, ran the engine, bled it, refilled etc. etc.

Where oh where has my hot air gone...

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Marty,

You may already have the factory repair manual but if not this might help. There are numerous possible explanations as to why you're not getting any heat. A plugged heater core is certainly one of them but you could easily verify if coolant is flowing in and out of the heater just by grabbing the return hose. You'll feel the coolant in the hose if you squeeze it enough to provide a restriction. Other explanations include a failed actuator, a failed interior temperature sensor or maybe a failed coolant temperature sensor.

TROUBLE SHOOTING

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. See Fig. 3 or 4. Press OFF button to

cancel actuator check mode.

:)

Let me know if you need more information. I can send you a link to the factory repair manual for a '95 SC400.

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I just wanted to add that replacing the heater core would be a royal PITA and that's why shops charge an arm and a leg to do that since it often requires dismantling or removing the dash. If the car was used in a temperate climate like Hawaii, Florida, South Texas etc then it's possible that the coolant in the heater core never got circulated which could lead to a heater core failure. If the heater was run on any kind of the regular basis AND the coolant was flushed every year or two then I seriously doubt that the heater core is the problem. I would guess that it's a stuck door or a failed door actuator. If you run through the test procedures that I listed you might get lucky and find the problem.

Good luck.

:)

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I agree. PITA. Never done it - never hope to. By the way K9crew - nice procedure bud. That may be added to the tutorial. Thanks man.

Marty - the car may also be vapor locked where an air bubble is in a high spot of your coolant system. Perhaps a pesky bubble of air is in a bad place. I'll be back with more if needed - let me grab some time. Do that test procedure. I'm curious how that will work out. B)

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AWJ and SK,

I just copied the information from the '95 SC400 repair manual that I bought on eBay. I think it's amazing that the A/C controller has a built in diagnostic tool ... very cool!!

:)

I'm learning about these cars along with everyone else.

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AWJ and SK,

I just copied the information from the '95 SC400 repair manual that I bought on eBay. I think it's amazing that the A/C controller has a built in diagnostic tool ... very cool!!

:)

I'm learning about these cars along with everyone else.

well lexus are a remarkable vehicle

as the slogan goes

"have you driven a ford latley"

lol

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SK,

I happen to own a '02 Ford F-350 7.3L dually and it's AWESOME. No creaks, rattles, leaks or problems of any kind in almost two years!! I also have a '98 Jeep Wrangler that I abuse on weekends on some tough trails. That vehicle has 42K trouble-free miles on it. I'm not one of those that subscribes to the theory that Japanese vehicles are perfect and American vehicles are a POS. This '95 SC400 is fun but it ain't no PSD!!!

:)

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ford trucks though

are the damn good

i will say that for beating on every day

the fit and finish iss another thing completly

but it is made to work not really go to the opera

but i am sure in texas it doers alot

they seem to sure love there trucks there

( i haven't travelled in the states too much out of the big citys)

kinda perfer chevy trucks for durability

and dodge rams for looks

but it is all so opinionated

everyone likes different things

and in 2 years you must have really gotten a real good one

i used to go by the f 150 truck plant outside toronto and they didn't have that may defects in the line

as comapred to the windstar

whiich had a huge row of lines for defects to fix

which hapened to be next door to each other in oakville

the 350 is a beast though

all you need now i a turbo k9,

as the 7.3 is gas right? :blink:

:cheers:

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all you need now i a turbo k9,

as the 7.3 is gas right?

The 7.3L is a turbo charged diesel engine. 275HP and 525lb-ft (@1600rpm). :lol: I have a 65:1 crawl ratio, a 6spd manual trans and a 4.11 rear end ... anyway, there are other boards to discuss my F-350 (excellent fit/finish by the way) ... I won't mention it again .... :unsure:

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Wow, you guys are great. I will give the diagnostics a try. My coolant is a reddish color by the way.

I will keep you filled in. I am working on getting a set of manuals for a 1997 SC400. I assume that the 95 and 97 will be almost exactly the same??? Any comments??

Marty

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K9CREW, you is da man!!!! I just tried the sel diagnostics and got trouble codes 21 & 41. The number 21 is the solar sensor unit, but is was dusk when I did the test. Besides, it works fine.

But, code 41 "Air mix door servo motor circuit" could be the jack pot!!!! It sounds like it makes sense to me. Got anything in the manual to solve this code K9Crew???

Let me know.

Thanks to everyone who is helping out.

Marty

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On a ford?? Must be a Hawaii thing.

... no comment! :D

Marty,

I'll check the manual today. I've been so busy trying to solve my own SC400 problems that I haven't checked the board in a few days ... sorry about that. I'll try to make a post around 1:00pm (PST). That A/C heater diagnostic feature is excellent!! I've yet to try it but the 41 code that you received does make sense. If the air mix door isn't opening then you won't be getting any heat.

:)

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Marty,

Here's some information on diagnosing faulty actuators.

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. See Fig. 3 or 4. Press OFF button to

cancel actuator check mode.

AC.jpg

AC2.jpg

I hope this helps.

:)

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CODE 31 OR 41 - AIR MIX DOOR POSITION SENSOR CIRCUIT

NOTE: For Code 41, also see CODE 41 - AIR MIX DOOR SERVOMOTOR

CIRCUIT for additional trouble shooting procedures.

Voltage Check

1) Remove A/C-heater control panel, leaving harness

connectors attached. See A/C-HEATER CONTROL PANEL under REMOVAL &

INSTALLATION.

2) Turn ignition on. Backprobe between terminals A12-22

(Green/White 6wire) and A12-20 (Brown wire) of A/C-heater control

panel connector. See Fig. 5.

AC3.jpg

3) Measure voltage while changing set temperature to activate

air mix 6door. See AIR MIX DOOR POSITION SENSOR CIRCUIT VOLTAGE

SPECIFICATIONS table.

4) If voltage is as specified, temporarily substitute a

known-good 6A/C-heater control panel, then retest system. If voltage

is not as specified, measure sensor resistance. See SENSOR RESISTANCE

TEST.

AIR MIX DOOR POSITION SENSOR CIRCUIT VOLTAGE SPECIFICATIONS TABLE

Set Temperature (1) Volts

Maximum Cool ................................... 3.70-4.27

Maximum Hot .................................... 0.88-1.16

(1) - As set temperature increases, voltage should gradually

decrease.

CODE 41 - AIR MIX DOOR SERVOMOTOR CIRCUIT

NOTE: Also see CODE 31 OR 41 - AIR MIX DOOR POSITION SENSOR CIRCUIT

for additional trouble shooting procedures.

Actuator Test

1) Warm the engine to normal operating temperature. Perform

step 1) under RETRIEVING CODES. After system enters diagnostic code

check mode, perform actuator check. See ACTUATOR CHECK under TROUBLE

SHOOTING. Observe air mix door operation. See appropriate AIR MIX DOOR

AIRFLOW table.

2) If air mix door functions as specified, no problem is

indicated at this time. If air mix door does not function as

specified, test air mix door servomotor. See AIR MIX DOOR SERVOMOTOR

TEST heading below.

AIR MIX DOOR AIRFLOW TABLE (1995)

Display Code Door Position Condition

20-22 ..... Fully Closed ............ Cool Air Comes Out

23-24 ...... Half Open ... Blend (Cool/Hot) Air Comes Out

25-27 ...... Fully Open .............. Hot Air Comes Out

AIR MIX DOOR AIRFLOW TABLE (1996)

Display Code Door Position Condition

0-2 ........ Fully Closed ........... Cool Air Comes Out

3-4 ......... Half Open ... Blend (Cool/Hot) Air Comes Out

5-7 ......... Fully Open ............. Hot Air Comes Out

Air Mix Door Servomotor Test

1) Remove air mix door servomotor. Refer to

AIR MIX DOOR SERVOMOTOR R & I under REMOVAL & INSTALLATION. Unplug air

mix door servomotor connector.

2) Connect battery voltage to air mix door servomotor

connector terminal No. 5 (Violet wire). Connect terminal No. 4

(Red/Yellow wire) to ground. See Fig. 8. Air mix door servomotor lever

should move to cool air position. Transpose battery and ground leads.

Servomotor lever should move to hot air position.

AC4.jpg

3) Replace air mix door servomotor if it does not function as

described. If servomotor functions correctly, inspect wiring harness

and connectors between servomotor and A/C-heater control panel. Repair

as necessary. If wiring harness and connectors are okay, temporarily

substitute a known-good A/C-heater control panel, then retest system.

:)

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