No Heat

[mondialneil]

Hi All

I am a member on the 911uk forum and 986 forum but no one seems to have an answer for my below problem.

Well it has been 8 months since I last had my 2001 2.7 Boxster out to play.

The trouble is my heater is not putting out warm air when it is set manually anywhere between 18 to 29 on AC or none AC mode, you only get very hot air immediately if you set heater to high.

Is this a known problem with a fix, I have read one problem that lay with the heater gate being full of holes after all the foam has broken down on it.

I have taken the heater core out and there is no foam anywhere in the box, the foam on the flap is all intact and in very good condition, no signs of breaking down.

I do have a question about the flap.

When the heater is put on high the flap completely opens.

As soon as you set the temp to just below high the flap completely shuts, so at 29.5 c I get cold air and all the way down the scale to 22 c.

Should the flap close in a graduated fashion when you go down in the temp scale, if it should then this is my problem as the door just completely shuts when not on the high setting.

The core is also not blocked and heated coolant flows through it.

Has anyone got any other ideas what this could be.

Thanks

Neil.

[Ahsai]

Sounds like the servo that controls the flap is not providing the correct feedback of the flap position? Have you tried to bench test the servo?

You can hook up a 5v supply (from any USB power plug) to the potentiometer of the servo (pin 3 = 5v, pin 1 = 0v), then power the servo motor with a 9v battery (on pins 4 and 5, or 6, can't tell for sure in the diagram). Diff polarity will move the arm in diff directions. You can then check the potentiometer output (pin 2) and verify that it outputs 0.5v to 4.1v smoothly and continuously when the arm sweeps through its full range of motion in both directions.

junk3.pdf

[mondialneil]

Hi Ahsai

I will check the servo.

So the servo should move the flap bit by bit when you change the temperature setting ?

Cheers

Neil.

[Ahsai]

Hi Ahsai

I will check the servo.

So the servo should move the flap bit by bit when you change the temperature setting ?

Cheers

Neil.

Exactly. The servo should move the flap proportional to the temp setting. It should be able to stay partially open so it can modulate the air temp by mixing the right amount of hot air with cold to get the exact temp setting you chose.

In other words, as you change the temp setting gradually, the flap should move bit by bit. That's why there's a potentiometer inside the servo that provides a varying output depending on the degree of opening of the flap. I hope that makes sense.

[Ahsai]

Another maybe simpler failure point could be the interior temp sensor, which maybe sensing HOT all the time so the control unit decides to close the air mix flap to avoid hot air. When you set the temp to Hi though, maybe this sensor is bypassed so its faulty input won't matter.

You can check it with Durametric or check the voltage of pin B6 of the control unit

0c->3.7v

23C->2.5v

35C->1.7v

Also, there's a temp sensor called output footwell sensor, pin B7 of the control unit

0c->4.2v

23c->3.2v

35C->2.6v

Of course if you use Durametric, it can also retrieve any a/c related error codes.

Edited June 4, 2014 by Ahsai

[mondialneil]

Ahsai

Thanks very much for the help and information. :thumbup:

[mondialneil]

Yes Yes Yes it is sorted.

It was the cabin ambient temperature sensor, the one that sits behind the passenger side air vent.

One of these came up on Ebay for £10 secondhand so I bought just to try as it was not too expensive.

Also I had read above from Ahsai this could be a culprit and it was.

Happy chap now lol

Edited June 6, 2014 by mondialneil

[Ahsai]

Glad you got it sorted out and it's a simple fix!

[mondialneil]

Ahsai

Thanks, it was you who gave me the info.