355 heater temperature valve problems. Help!

That is the ABS ECU pictured. The AC ECU is back up under the dash behind the bank of relays shown in the picture.

 

I just developed the same issue. Ive tested everything. I even have 3 hvacs that I tried. Everything works including that little motor you just bought. Ive come to the conclusion its the ac ecu cuz something isn't sending a signal to that little motor to open and close. There is supposedly a reset procedure for it but I ve tried it several times but it didn't work

 

Also, you can test the motor by disconnecting the plug and apply +/- 12 V across the pins where the yellow/black and red/white wires were connected. + volts moves the valve one way, - volts the other. I believe they are the outer pins in the receptacle on the valve housing. DO NOT connect any power to the plug on the end of the harness.

If the valve moves when you do this it means that you are not getting power from the ECU.

 

Here are some "Sensors" that may need to be part of the diagnostic checklist:


1. Outside Air Temperature Sensor located on the Driver Side Rear View Mirror

2. Cooled/Heated Air Temperature Sensor(also known as Treated Air Sensor)...

3. Evaporator Temperature Sensor

4. Passenger Compartment Sensor(Very Important as this Sensor is used to compare with the control unit knob setting on dashboard which in turn variate s the heater valve stepper motor)


If any of these are not working the microprocessor(ecu) cannot compute logic(one of its many functions is to control the stepper motor on the heater valve)...

 

Do you know how to test these sensors.

 

Anyone who is knowledgeable about "Negative Temperature Coefficient Thermistors", and has the equipment can test these.

I believe all of these are the NTC type but someone else may want to comment

Maybe JohnK can help out

 

I'm currently looking at a friend's 355 and the heating/ac works properly including the stepper motor however when turned on the stepper motor closes the flap. Take the stepper motor off and reset it again to full open, it closes the flap once plugged in and turned on. Am going to to take a look at the sensors next as it appears one has failed.

 

If they are NTC or PTC they should have 2 wires. To test you would just measure the resistance between the two wires and check if it varies if you heat the sensor up, say with hot air from a hair dryer. That would at least show they were responding, but without know the rated resistance (for example they come in 100 ohm, 1000 ohm, etc) it's hard to say they are ok. But chances are, if the resistance is changing smoothly with heat and cooling, it's ok.

By the way, I'm following this thread closely because I have the same issue. When out for a drive on a cool day and heat was working fine. Next time out it was warmer and I could not shut the heat off. Checked the valve and it was working fine. I applied a voltage to close it and everything works: AC, air direction, Fan speed, temp selection (as long as cooling is required) but heater valve will not open even if I set the controls to manual and the temp selector to max heat (red dot). I setup a little circuit to tell me if power was being sent to the valve and wither it was being asked to open or close. No power either way. No signal from the AC ECU. Being winter now, I' not playing with it and come spring I think I may just have a diagnostic run on it unless something come of this thread.

Would love to have an AC ECU to swap though.

 

Different problem. If you are talking about the recirculation vent flap, if the button is not depressed it is supposed to open and close based on time and/or outside/inside temperature. If the button is depressed it will close. This is discussed on the owners manual.

 

Ok,the WorkShop Manual Volume 3-Section "Air Conditioning" is saying they are "NTC" type.

I agree that the big issue in testing is what values are considered "within limits", according to the logic program in the ECU.

 

Yes I'm aware of what the manual says.
Whats happening here is the flap is closing and never opening despite any of the settings.

When the stepper motor is removed and manually reset (12 volts)to open position and then reinstalled (with flap open).....car is started & the flap closes (regardless of where the settings are ) and never opens again although the ac , defogger and heating are working perfectly.

 

#8 and #13 in Diagram

Cabin Sensor is circled in yellow in pic
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Chris ive done all that. The only things I haven't checked is the sensors that bruce has mentioned. im going to try to test them as well. keep us posted please

 

Not Bruce, but yes, 46 is the AC ECU. As I said, it is mounted behind the line of relays which was along side the ABS ECU shown in your earlier post. Under the windshield area.

 

This is timely for me as of this weekend. Took my 98 Landcruiser to a place to have a remote starter installed. Picked up the truck and when heater controls were set to auto the fan blew at full speed regardless of the temp dial setting. It would switch from heat to Ac and change the ducts but the fan was on high all the time. If I took it off of auto I could control it manually.

Went back to the shop and explained it to the owner and asked if he had any ideas. He said right away, yes. He came out and said the passenger sensor was unplugged and he had plugged it back in. He unplugged it and all is well. He said the sensors sometimes get clogged and people unplug them although I never did but my point is in this case that plugging the sensor in made things whacky.

So to Bruce's point , maybe it's a sensor issue.

 

Me about it. Snowing again today in New England. 23* F. Fortunately, I have a spider and don't driver it in winter.

 

Here are the values of the four sensors in the 348, should be similar in the case of 355.
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