Special Functions

SPECIAL FUNCTIONS

The IHKA control module is programmed to perform some special functions automatically based on sensed inputs and ignition switch cycles. These functions are described below.



Cold-Start Arrest







If, at engine start-up, engine coolant temperature is below 86 °F (30 °C), and the left Y-factor is 100%, the control module automatically initiates the cold-start arrest function. The purpose is to avoid cold drafts in the passenger compartment.


NOTE: Cold-start arrest is overridden if the "maximum defrost" program is selected or if the blower control thumbwheel is in the maximum speed detent position at engine start-up.


Cold-start arrest operation is as follows:
- The defroster flaps are fully opened; at other air distribution flaps are fully closed.
- The blower runs at very low speed (3 volts).
- The A/C compressor is turned "Off".
- The auxiliary coolant pump is turned "Off".

The control module monitors the coolant temperature as the engine warms up:
- When coolant temperature reaches 68 °F (20 °C), the module increases blower voltage with temperature.
- At 86 °F (30 °C), the A/C compressor is enabled, the auxiliary coolant pump is turned "On", and air distribution is determined by control panel button positions.
- Above 122 °F (50 °C), blower voltage is determined by blower speed thumbwheel position.

Beginning with software version "03" (from 12/88 production), the A/C compressor operates during cold-start arrest if the A/C compressor push button is depressed, to help prevent window fogging following engine start-up.


NOTE: Also beginning with software version "03", if the IHKA system is "off", at engine start-up and remains "off" as the engine warms up, the blower motor turns off automatically when the cold-start arrest function ends.


Service-Station Feature







Beginning with software version "03" (from 12/88 production), the IHKA control module continues to power both coolant valves closed for about 3 minutes after the ignition is switched "Off." This feature prevents the heater cores from being flooded with hot coolant when the engine is shut off for brief periods (e.g. during refueling).




Calibration Run

If the battery is disconnected, IHKA control module memory is cleared and the module loses its information about where the flaps are positioned. Therefore, when power is restored, the control module performs a calibration run, whether the IHKA system is turned "On" or "Off".

The control module runs all the stepper motors at maximum speed to fully close the flaps, and then continues to run the motors for a few seconds more than the normal endstop-to-endstop time, in order to ensure the flaps are closed.

The calibration run takes about 40 seconds. During that time, soft "ticking" or "scratching" noises can be heard, as the flaps reach their endstops but continue to be pulsed.

The control module also monitors system voltage. A sudden surge or dropout causes the control module to automatically perform the calibration run.