944 Heating System — Overview & Fresh-Air Blower

The heating group in the 944 Workshop Manual is deliberately thin: from the 85/2 model the car received a revised heating system that shares its housing and most of its service procedures with the air-conditioning system, so the manual points there for removal, installation, and overhaul of the combined heater/A-C unit. What the heating and ventilation groups add on their own is the fresh-air blower service and — for the later controllable seat heating — a calibration table. This page collects that data.

Revised heating system (from the 85/2 model)

From the 85/2 model all 944 vehicles use a new heating system. The key difference from the earlier design is that all flap control is by electric control motors or by vacuum pressure rather than by mechanical cables. The dash controls are:

1. Defrost switch
2. Outside-air blower switch
3. Defrost slide switch
4. Footwell slide switch
5. Temperature switch
6. Ventilation switch

As a special option there is an automatic heating system with a temperature-preselection switch: once a target interior temperature is dialled in, the system regulates and holds it on its own, as long as the outside temperature is below the preselected value.

The heater and, where fitted, the A-C evaporator live in one combined heater/A-C unit. Several of its assembly parts are omitted on cars without air conditioning. For removal, installation, disassembly, and assembly of that unit, see the air-conditioning system reference — the manual handles the whole heater/A-C box under the A-C repair group rather than under heating.

Fresh-air blower — removing and installing

The fresh-air blower sits in the fresh-air well ahead of the windscreen (the "cowl"), so access is from the top of the engine bay. This procedure applies since the 1985/2 models.

1. Remove the fresh-air well cover. Disconnect and pull off the windscreen-wiper arms, pull off the rubber seal from above, and loosen the cement of the cover beneath the windscreen. Done carefully, the cover can instead be folded up against the windscreen, in which case the wiper arms need not come off.
2. Unscrew the fresh-air blower mounting screws.
3. Disconnect the plugs.
4. Lift the fresh-air blower slightly and pull off the inner vacuum line.
5. Check the sealing cord of the fresh-air blower and replace it if necessary.

Tip: The sealing cord keeps water out of the blower well. Inspect it whenever the blower is out and renew it if it is hardened, torn, or no longer seating — a poor seal lets rain into the fresh-air path.

Installation is the reverse. Refit the inner vacuum line and the plugs, seat the sealing cord, and reset the wiper arms to their parked position if they were removed.

Fresh-air blower motor — removing and installing

To reach the motor and fan wheels, split the blower housing after the blower assembly is out of the car.

1. Remove the fresh-air blower (above).
2. Unlatch the plug connector in its holder.
3. Undo the cable straps.
4. Pull off the vacuum hose.
5. Undo the fastening screws.
6. Lay the blower housing on its upper part and lift off the lower part.
7. Take out the blower with its fan wheels.
8. Undo the nut.
9. Take off the fan wheel.
10. Remove the disc.
11. Remove the second fan wheel.

When reassembling, make sure the air-circulation flaps are seated correctly and that the engine-ventilation hose is correctly fitted between the upper and lower parts of the housing. Carry out a functional check on the air-circulation flaps before refitting the blower in the car.

Fastener	Tightening torque
Fan-wheel nut	3 N·m2 ft·lb

Controllable seat heating — calibration

The heated seats fitted from the model 89 onward use a control unit that must be recalibrated after the control unit or a heating element is replaced. Calibration sets the control unit's reference to the current ambient temperature so that the thermostat regulates correctly.

The control unit for seat heating without seat-position control has two features used in this procedure: a set of measuring points (A) and an adjustment potentiometer (B).

Tools

• Digital voltmeter with an internal resistance (Ri) of at least 1 MΩ.
• Two measuring probes, maximum 2 mm diameter.
• Thermometer (as recommended in the Workshop Handbook).
• 2 mm wrench.
• Two auxiliary cables to feed voltage to the removed seat (terminals 15 and 31); use adapter cable 9269 for seat-position control.

Procedure

1. Store the seat in the working area until it has taken on the ambient temperature.
2. Provide the power supply.
3. Measure the ambient temperature and read the corresponding voltage from the table.
4. Connect the voltmeter to the control unit at the measuring points (A).
5. Set the voltage on the calibration potentiometer (B) so that it matches the value for the measured ambient temperature.

Caution: Do not switch on the seat heating during calibration. If it is switched on by accident, let the seat cool until the heating elements have returned to ambient temperature before continuing — otherwise the reference reading is wrong.

The setpoint rises by 0.025 V per °C across the whole table (1.50 V at 0 °C32 °F up to 2.70 V at 48 °C118 °F). Read the exact figure from the table rather than interpolating by eye.

Ambient temperature	Voltage
0 °C32 °F	1.50 V
2 °C36 °F	1.55 V
4 °C39 °F	1.60 V
6 °C43 °F	1.65 V
8 °C46 °F	1.70 V
10 °C50 °F	1.75 V
12 °C54 °F	1.80 V
14 °C57 °F	1.85 V
16 °C61 °F	1.90 V
18 °C64 °F	1.95 V
20 °C68 °F	2.00 V
22 °C72 °F	2.05 V
24 °C75 °F	2.10 V
26 °C79 °F	2.15 V
28 °C82 °F	2.20 V
30 °C86 °F	2.25 V
32 °C90 °F	2.30 V
34 °C93 °F	2.35 V
36 °C97 °F	2.40 V
38 °C100 °F	2.45 V
40 °C104 °F	2.50 V
42 °C108 °F	2.55 V
44 °C111 °F	2.60 V
46 °C115 °F	2.65 V
48 °C118 °F	2.70 V

Functional check: switch on the seat heating for about 10 seconds at maximum heating power. After switching off, measure the voltage at the control unit again — it must now be considerably higher than the calibrated ambient value.