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 Post subject: ST205 heater problem.
PostPosted: Tue Nov 15, 2011 7:31 pm 
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Location: Bournemouth
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Just wondering if anyone can make a few more suggestions to try or has a full wiring diagram of the JDM climate control system.

Symptom is that with the temperature control below 20 I get cold air (even colder with aircon on, although I think it controls to 16). With it set above 20 I get full heating. The set position doesn't ever change regardless of temperature.

So far, I've measured what I think is the thermistor (comes out of heater unit passenger side (RHD car) at the bottom and resistance goes down with hot air & up with cold. Have changed the control panel with knob & buttons and the 'aircon amplifier' located just above ECU.

The wiring diagram in RM399 doesn't appear to be a full wiring diagram and doesn't show heater servo etc.

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PostPosted: Tue Nov 15, 2011 9:32 pm 
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Joined: Fri Mar 31, 2006 7:29 am
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Location: Up North
Car Model: ST205
I am only guessing here, but when you set the temp up wont it run hot until it gets to 20deg then keep it at an even temp???? or isnt it that clever?

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PostPosted: Tue Nov 15, 2011 11:42 pm 
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It's meant to control the temperature at what you set in a normal proportional servo fashion

It appears not to be measuring temperature as the temperature setting it goes from cold to hot doesn't change. It also seems to have gone high gain as it goes from fully cold to fully open with just a whisker of movement on the control, normally it would be over a few degrees.

If it were a servo motor feedback problem would explain the high gain but I'd expect the set point to be at whatever temperature the thermistor is at.

I'm wondering if there's more than 1 thermistor and it's another one gone wrong. The drawing I have only shows one but I know it's not a full drawing or may be for a different version.

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PostPosted: Wed Nov 16, 2011 12:06 am 
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Location: drinking devil fuel
Car Model: ST205
there's a sun load sensor behind the instrument binnacle too but I have no idea where that fits into the picture

Have you checked the water valve hasn't got sticky - maybe it only responds to large inputs and hence becoses a limit->limit type switch


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PostPosted: Wed Nov 16, 2011 12:09 am 
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Location: drinking devil fuel
Car Model: ST205
PS
if it's any consolation my Mondeo' vacuum operated heater system :shock: has sprung a vac leak somewhere behind the dash so I have to put up with roasted eyeballs and frozen feet :lol:


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PostPosted: Sat Dec 21, 2013 12:57 pm 
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2 years I've been suffering with an on off heater and had to cycle manually between roast and freeze. Now I've finally found the problem after examining a scrap shell which has had the dash removed.

My suspicions were correct, there is another thermistor under the dash, but it's hardly hidden. There is a small (15mm dia) pipe coming from the heater system at the back, driver side which feeds outgoing air to the sensor mounted on the trim under the steering wheel. In my caser, I'd obviouly removed this to access something and not put the plug back in or not noticed it dropping out (it just pulls out if pulled at a slight angle).

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PostPosted: Sat Dec 21, 2013 2:28 pm 
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Ahh I've seen a similar thing on my CS, that tiny vent, always wondered what it was for !

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PostPosted: Sat Dec 21, 2013 2:37 pm 
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I didn't realise the 185's had a climate control option. My JDM one is the conventional manual control.

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PostPosted: Sat Dec 21, 2013 4:06 pm 
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Location: Perth, Western Australia
Car Model: ST205
Same for the 205's. My UK had manual control A/C heater and my JDM is climate control A/C heater.

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1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
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PostPosted: Sat Dec 21, 2013 4:17 pm 
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As far as I'm aware, on 205's the JDM normally have 'climate control', the UK have manual. All the handbooks I've found only cover the UK version hence no ability to diagnose my system.

I can only assume is was an optional extra on 185's, or maybe was fitted to the RC/CS being the special version.

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PostPosted: Sat Dec 21, 2013 4:31 pm 
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Location: Camberley, Surrey
Car Model: ST205
Yeah doesn't seem clear cut with the ST185's if yours has manual control, my ST185 had climate. It was a 1991 Widebody version

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