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The mkiv Supra Owners Club

Heater/Blower Stuck on Low Speed


Eightdip
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Hi all!

 

I've tried searching everywhere for a solution but not seen anyone with the same issue as me.

 

I have a 95' SZ Jap import in which the heater/blower will only ever go to the lowest speed. The lights on the dash work and the blower itself does turn off if I press the 'off' button. Also the temperature is only every blazing hot or freezing cold, no in between. All fuses are ok, I've replaced the blower motor relay in the passenger footwell, everything looks ok on the insides of the dials unit and I also replaced the interior temperature sensor (thermister?) in the dashboard yesterday but still no luck.

 

Does anyone have any ideas?

 

Much appreciated!

Piers

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Check if the flap isn't stuck closed. It's the one behind the dash, passenger side. Theres an arm attached to a white flap that moves between hot and cold. Last resort is taking out the lower and uppger gloveboxes to see if the pipes are connected properly.

 

I'll have a look asap, I'd assume if any pipes weren't connected properly it wouldn't affect the fan speed?

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I'll have a look asap, I'd assume if any pipes weren't connected properly it wouldn't affect the fan speed?

 

I'm confused now. Are you checking the fan for the speed or how hard it blows out the vents? If one of the pipes are off, all the air would blow into the nearest hole and only a little would reach the vents as there isn't enough pressure to push the air out all the way to the vents.

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I'm confused now. Are you checking the fan for the speed or how hard it blows out the vents? If one of the pipes are off, all the air would blow into the nearest hole and only a little would reach the vents as there isn't enough pressure to push the air out all the way to the vents.

 

The blower itself only works at low speed, I would hear if the actual unit was working at higher speeds and not making it to the vents but it isn't.

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Have you tried run hvac unit diagnostics?

 

http://www.jack-frost.co.uk/toyota_supra_air_con.html

 

According service manual (electrical)

-The motor is connected to blower motor relay box.

-Blower motor relay box gets signal from ac amplifier, what speed is needed.

-Ac amplifier gets signal from dash unit if not on "auto" mode

 

If motor itself works the broblem is between

1. Dash unit vs ac amplifier

2. Ac amplifier vs blower motor relay box

3. Blower motor relay box

 

I would start by reading those codes... if nothing, then by measuring, with voltage meter, that blower control box gets current to control signal input wire.

 

Also, trying with other working ac amplifier / dash unit could lead to symptom...

Edited by kaahari (see edit history)
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  • 2 years later...

Just picking up on this thread, so after trying myself to diagnose and failing miserably, I spent a few hours on it today with an actual capable mechanic and we think it could be the AC amplifier not functioning (part 88650-14270, though maybe different on my J-Spec?).

 

I was super confused with the system as a whole, not realising that the ac amplifier and dash control unit was actually 2 different things (even though it definitely says that above, I just didn't quite get it), the amplifier being presumably hidden somewhere in the depths of the dashboard.

 

I believe the dash control unit has been replaced in the past as it has a part number written on it in tipp-ex (seems like a replacement used part), I've changed the blower motor relay and internal temp sensor, we confirmed today that the blower does indeed work if we send voltage to it so presumably the only option left is the AC amplifier unless anyone else has ideas?

 

Does anyone know of one for sale/where I could get one? I'll try toyota tomorrow but not holding out much hope, will also try Garage D.

Edited by Eightdip (see edit history)
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