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Gallagher99, Senior Vehicle Technician
Category: Ford
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Fiesta LX 1997 1.25 16V Heater Blowing hot air. I have replaced

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Fiesta LX 1997 1.25 16V
Heater Blowing hot air.
I have replaced the heater valve on the bulk head.
Still blowing hot air.
I have checked the voltage at the two cables connecting the heater valve.
Cable 1 - Is purple/black and is 12V when at pre-ignition. This cable bells out to earth.
Has it shorted out?
Cable 2 - Is green/black and is 0V when at pre-ignition.
I have bought a second Heater Control Panel and fitted it.
Cable 1 - Is purple/black and is 12V when at pre-ignition. This cable bells out to earth.
Has it shorted out?
Cable 2 - Is green/black and is now 4.56V when at pre-ignition.
Heater still blowing Hot air
Hi there good evening to you
Ok the heater control valve has 2 wire going to it
it has a 12 volt feed on the violet/black wire ( this is powered from fuse 13 ( 15amp)
this is located in the CJB ( just under the steering wheel to the right handside )
also ensure that fuse 2 ( 7.5amp) in the CJB is ok as this powers the heater control panel ,
the heater control valve is controlled/opened using a variable earth from pin 5 at the heater control panel to pin 2 at the heater control valve ( black/green)
if the heater control valve has been replaced then i would rule this out
the easiest way to check if the heater control panel/wiring to the heater control valve is working is to dissconnect the multiplug and connect either a noid light or a circuit tester ( using a paper clip etc)
and put the temperature dial to the middle ( the light should pulse )
if you turn the dial to fully cold the light will stay constant if you select hot the light will go out as there is no feed and earth

Pin 1 has 12 volts to it the other side is the variable earth to operate the valve (close it )

i have changed a few of these control panels ( usally after someone has replaced the valve)
The heater control valve is in open position (hit air ) with the multiplug dissconnected )

You can use a multimeter if you don't have a noid light go across the 2 wires with the plug connected (leave it connected so the wiring is loaded (this way either nick into the wiring or use a paper clip to back prove the plug

You cannot test wiring with the multiplug connected unless a noid light is used

So with multiplug connected across the 2 pins/wires

Hot = 0 volts
Cold = 12volts +
Middle = fluctuation between 0&12volts

if you need anymore help or advice on this issue please let me know
if you are completley satisfied with my answer/advice PLEASE CLICK ACCEPT
Kind regards ***** ***** and have a nice evening
Customer: replied 3 years ago.

Hello and good evening.

I have already carried out this test.

I used a side repeater bulb(I thought this a sufficient load to test with) and plugged it into the two pin plug

that connects to the heater control valve and turned the plug through the three positions.

The bulb did not light in any.

I then assumed that the original heater control panel and the replacement(Second hand) I had bought where both broken.

If it did light I would expect the heater control valve I had purchased new was broken.

Hi there thanks

Ok can we carry out a few tests with the plug connected and ignition on

1- measure (back probe or nick wiring ) violetv/black to battery negative you should have battery voltage
If you don't then this is where the issue lies this you cannot check voltages with plug dissconnected

We need to find out which side the issue lies (feed or earth )

Regards Brian
Customer: replied 3 years ago.


Violet/Black and ignition off 0v

Violet Black and ignition on 12v

I have put a nick in each of the two heater control valve cables.

I turned the ignition to pre-ignition.

I then tested the voltages.

In the green and black cable the voltages.

Cold setting - 12v

Mid setting - Pulsed between 9.5v to 12v

Hot setting - 12v?

Does this mean that the heater control panel is broken.

Cheers Andrew.


Hi Andrew thanks

Was this last test across the 2 wires if the heater bakve with the plug connected

Regards Brian
Customer: replied 3 years ago.


The previous readings where:-

With the two wire plug ( Violet/Black and Green/black wires) connected to the heater control valve.

The previous readings where to earth point on the car to the green/black wire

New readings below where taken across the two wires and with the plug connected to the heater control valve.

Across the two wires

Cold setting - 0v

Mid setting - 0.56v Fluctuating

Hot - 0V

Cheers Andrew.

Hi there thanks

Ok the fault lies in the earthing side this is used to close the valve

We know the feed to the valve is ok at pin1 violet and black as we have 12 volts with ignition on and connected at this pin to battery negative

The variable earth from the panel is what closes the heater valve and makes it operate for cold air

Basically you should have a constant earth at the cold position setting this moves the valve to closed position not allowing any hot coolant to glow through the valve

The variable earth leave the panel at pin 5 of the heater control panel so if you put an earth up this wire the heater control valve should operate thus you get cold air

I would suspect a faulty panel in this case

Regards ***** *****

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