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  Climate Control

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AC - How it works
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Pollen Filters
Test the HBC
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A/C Manual
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Scorpio fitted with Climate Control

Scorpio without Climate Control

a/c evaporator housing and parts

a/c control panel

condenser & dehydrator assy

evaporator housing & components

a/c & heater housing

heater housing

a/c heater ducting

a/c heater ducting

a/c compressor
Air Conditioning is standard across the Scorpio range however on higher marques such as the Ultima, Climate Control is fitted as standard and was an optional extra on lower spec vehicles.
The climate control on the Scorpio is an extremely sophisticated system, well ahead of its time when you think that it was introduced in the new model back in 1994. Even today on brand new cars that do have cc installed it is rare to find vehicles that have a “dual” system such as is fitted in the Scorpio. This enables two different zones for temperature to be set one for passenger and the other for the driver.

To help the new driver become acclimatised (excuse the pun) to the system they even provided an Audio Cassette with the vehicle.

Note: If you can see the player controls then you have Real Player installed. Otherwise download it from here (choose the free link at the bottom)
Alternatively click here to download the MP3 version

Firstly we will run through the operational aspects of the system which should not be confused with how an air conditioning system works which is covered here

The idea behind Climate Control is to maintain a steady preset temperature which is controlled by the occupants of the car, it’s a bit like setting the thermostat on your home central heating system to maintain a set temperature in your house but this one is more sophisticated.

The cc system has a central processor located immediately behind the front display panel connected to the display by a ribbon that can be detached if the dash needs to be removed.

This processor receives inputs from :-


A temperature sensor mounted on top of the evaporator housing measuring external ambient temperatures.
A temperature sensor located in the middle of the cc control panel measuring internal ambient levels.
  Two temperature sensors located in the right and left front footwell air ducts.
A U/V photoelectric sensor located on top of the dash on the far right.
  A speed sensor measuring the car’s velocity.

These sensors are checked and monitored four times every second.

The unit also controls the air distribution motors and the air temperature blend doors as well as processing signals and controlling the other components of the air conditioning system such as the compressor and Heater Blower Controller (HBC).

The HBC is mounted on the blower plenum and is a solid state variable resistance. The fins are to cool down the electronics as it's resistance increases to slow down the blower motor.
Early versions of the HBC tend to overheat and cause problems so later ones are fitted with a larger (thicker) heatsink.

If you need to test your HBC then here is a suitable test document in PDF format

The whole system is designed to achieve the desired internal preset temperature as quickly as possible and then to maintain that temperature irrespective of the external ambient conditions.

The temperature controls of the cc unit can be set between 17 and 29 centigrade with additional settings of “Lo” achieving maximum cooling and “Hi” for maximum heating. As a matter of interest the Lo setting has a value of 15c and the Hi setting a value of 32c. For Fahrenheit buffs 17c equates to 62.6f and 29c equates to 84.2f.

Passenger temperature set at low

There has in the past been confusion over the operation of the cc system so we will run through a few of the basics.

Firstly don’t confuse the temperature of the air coming out of the vents with the temperature that you have set in the temperature windows on the control panel, they will rarely be the same nor should they be. A good example of this would be setting in a nominal setting of 21c/70f , on a cold day with an external ambient temperature of say 4c, the temperature coming out of the vents at least to start with can be in the region of 38c. On a scorcher in summer with the outside temperature of say 28c and with the temp setting on the cc unit still set at 21c the vent temps may only be 5 or 6c. I’m sure you can now see the logic behind the unit. Basically the set temperature is the temperature inside the car that the system will attempt to achieve and to do this it will pump in cold or hot air as required.

The system also has some clever features to achieve the desired temperature as quickly as possible, when the “Auto” setting is selected the system really comes into its own and in my opinion should be left in this position at all times if you are going to get the best out it. This not only controls the temperature of the air coming out of the vents but also the speed of the fans and under certain conditions the recirculated air function and the air distribution. For example if high cooling power is required when the ac is first switched on then the system will automatically switch to recirculated air to achieve maximum cooling even though the LED in the recirc switch will not illuminate. At the other extreme when the outside air temperature is very low the system will automatically go to the defrost setting for up to five minutes and will override the manual setting of the air distribution flaps pushing the air towards the front windscreen and it will set the air speed fans to low speed to avoid blowing cold air into the interior.

NOTE: When the system is set to AUTO and the Air Distribution control is set at Defrost the cc system will put the fan on as soon as the engine starts and run the air conditioning pump in order to demist the front screen - this can be disconcerting. If the Air Distribution control is set on any other position then the fan will not start to operate until the coolant temperature exceeds the interior temperature.

As has been said earlier the system also receives speed pulses from the speed sensor to tell the cc module what velocity the car is travelling at. This is used to control the speed of the fans to the air vents, for example if you are sitting in traffic in hot weather then it will instruct the fans to speed up, however if you are on the open highway doing 70mph then the air being forced naturally into the cabin makes high fan speed unnecessary and it will lower the fan speed accordingly.

UV Sensor, technically known as the SLD

Another very clever and well thought out sensor is the UV or sunlight load sensor located on the top of the dash, it's purple in colour and a lot of Scorpio owners are intrigued to know what it is and what it does.

Well let’s investigate the theory behind it first. All temperature readings that you see on weather reports and forecasts are taken in the shade, they are actually taken from inside a white painted box with louvers called a Stevenson screen. Say the temperature for example is 21c and its cloudy, it will feel exactly the same in the shady area of your garden as in an area where if the sun was shining it would be quite hot. Imagine then that the skies clear and now when you walk from the shady to the sunny area of your garden. Your body detects a noticeable difference in temperature as you feel the sun beating down on you. But has the temperature being reported in the shade of the Stevenson screen changed at all? Well hardly, maybe by a couple of degrees, but your body now in full sun will feel the effect of the direct rays of the sun markedly. And basically this is the idea behind the sun load sensor. The temperature sensors in your Scorpio may not be registering much change in the internal ambient temperature when the sun suddenly comes out, but you will feel the heat of the suns rays on your body and will feel much hotter. The SLD (sun load sensor) measures the intensity of the light falling on it and adjusts the cooling load of the cc to compensate for the suns heat. Clever eh!

A Stevenson Screen

So let’s just recap. When the cc is set to “Auto” the blower speed is changed continuously depending on the temperature setting, the amount of sunlight falling upon the sun load sensor, the outside temperature and the velocity of the vehicle.

You can of course deselect the auto operation and manually set the fan speed to one of 27 preset speeds.

As far as selecting temperatures for the passenger and drivers side these cannot exceed 6c difference, the driver’s side always has priority. The cc system always defaults to ac “on” when the ignition is turned, this can be manually switched off if required, after stopping the car the system remembers the settings for approximately one hour after the ignition is switched off. Also “recirculated” air can not be selected for 15 seconds after the car is first started to allow adequate ventilation of the system.



Just as the rest of your car needs looking after so does the ac system. It’s a good idea to have an ac health check once every couple of years.

Loss of the r134a refrigerant by natural seepage of between 60g and 130g per year is normal and as it is the refrigerant that carries around the lubricating oil to the ac compressor if you lose too much refrigerant then no oil will reach the compressor and it will seize, they are not cheap! Never has the philosophy “prevention is better than cure” been more apt.

Do ask for the complete a/c report which will give you vent temps, state of the system, high and low pressure readings, loss of refrigerant etc etc, keep these with your other servicing sheets and you will be able to keep an eye on the state of your cc system over the years giving you good forewarning of any impending problems.



Low pressure fill and guage valve with protective cap removed. Note the yellow UV dye is visible which is introduced during the service. Low pressure fill valve and pipework.

The a/c specialist will evacuate the r134a from the system, weigh it to determine the charge level, it will then be cleaned and any moisture removed. Whilst this is happening the ac system will be drawn into a deep vacuum which should be held for at least 30 minutes drawing any moisture out and checking for leaks. After this time the cleaned refrigerant is gradually re-introduced to the system a bit at a time and topped up with new r134a to the correct level to replace that lost in previous years, oil is also topped up at this time. A UV dye is also inserted so that leak testing can easily be carried out.

The high pressure fill and guage valve located on top of the receiver/dryer, the high pressure switch can be seen in the background. An example of the ac service report.
Note that on the sheet you can see that since the last service the charge level has fallen from the original 740g to 560g and it has been recharged with 1000g and oil topped to 160ml to comply with the issued tsb

You can do an easy check to see if your system is performing to spec. Buy yourself a cheap digital temperature probe, they don’t cost any more than a tenner and can be purchased from Halfords, Maplins, CPC etc. Firstly take an external ambient temperature reading outside the vehicle, make sure that the probe is in the shade and not in direct sunlight, make a not of this temperature. Then insert the probe a couple of inches inside the centre air vent, then start the engine, make sure that all windows and doors are closed, dial both passenger and drivers temperatures to “Lo”, set the fan speed to maximum speed, press the recirculated air switch to on, set the air vents to face level, run the engine at approx 1500 revs per minute and read off the lowest temperature reading on your digital probe within ten minutes. The diagram below shows centre vent temperatures that you should be getting if your system is within specification. You will notice the correlation between the outside readings and those at the centre vents.
Revs at just over 1500 rpm. Centre vent temperature reading showing a healthy 3.4c

A is the temp at the centre vent in centigrade, and B is the External temp.

For example if the external ambient is 15c then the vent temp should be between 3c and 6c. Readings in between the two lines on the graph are acceptable within spec.

Next time you have the hood up on your Scorpio take a look at the bright yellow sticker on the front cross member to the left of the car, this will tell you what charge of r134a and oil should be applied, if it says 740g of  r134a and 100ml of oil plus or minus 10% then you have the old fill capacities and you need to do some revision. In May 1995 a TSB no. 996/207 was issued increasing the amounts to 1000g of  r134a to improve cooling and 160ml of oil to prevent compressor damage. You will need to order a new yellow sticker from ford, part no.1 031 598, costing a few pence, to document the revised amount.


Old A/C sticker

New A/C sticker.

The next point probably will not readily apply to owners of Scorpios with Climate Control as if they have it fitted they will probably have it silently running in the background all the time, but if not then do make sure that the ac system is run for at least ten minutes every month, this keeps the compressor lubricated and prevents the o rings from drying out.

As you are probably well aware the system also filters and removes moisture from the air making it especially useful in the winter for demisting the windows. Pollen filters should be changed at least once a year, more often if you do a lot of your driving in polluted areas, when you put the new pollen, or cabin filters as they are sometimes called, they will be nice and white, when you remove them they can be very dirty even black. If you leave them too long they will eventually completely block up, preventing air flow into entering the cabin. The filters are very easy to change and are located in the evaporator housing just underneath the windscreen and easily accessed with the hood up, there are three of them for the Scorpio, simply undo the clips on the top of the housing, remove the black plastic lid and you will see the filters in front of the evaporator. Before removing them, note exactly which way they are fitted so that you can fit the new ones correctly, you may also want to order a pack of clips for the evaporator lid housing, they are only a few pence and if you were to drop one of the original clips then at least you will have some spare to hand. When fitting the new filters in place be extremely careful not to touch the fins of the evaporator itself, they are very delicate and easily damaged.

Evaporator with lid removed and pollen filters clearly visible, note the red lines indicate the top of the filters and the overlapping flaps should be at the front. The Evaporator with the filters removed and the delicate fins to the rear. Pollen Filters (there are 3 of them)

From time to time take a look at the ac condenser, this is located in front of the radiator at the front of the car and is of similar appearance, it is important to keep this clean and clear of debris, if this gets clogged by leaves or especially insects in the summer months the cooling ability of the system will be impaired. Take a water hose or preferably a compressed air line to this from time to time and spray straight directly onto the fins to clear any obstructions. Do not spray at an angle as this may cause damage to the fins.

(Viewed from underneath)
There are 3 'radiators' at the front of the
Scorpio. The rear most is the water coolant radiator,
followed by the Air conditioning condenser and finally
the smaller Automatic Transmission fluid cooler.

The Condenser mounted at the front of the car - this is not the radiator! Close up of the Condenser showing slight damage to fins and insects and debris that need removing. Do not inflict further damage.

For details of Fault Interrogation and Climate Control Reset see CC Reset





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