Room Thermistor:
Symptoms:
1.output low through all vents
2.on starting when set to medium heat on dial car will get warm inside
but once on the move a medium heat isn't possible. Either full heat or
nothing.
3.fan seems fine but air not getting out well except on max setting.
windsreen vents seem ok though.
Cause:
The room temperature thermistor is either cracked (failed) or dirty.
Fix: here
Room Thermistor Fan:
Symptoms:
When the ignition is on there is an annoying squealing/squeaking noise from the control panel.
Cause:
The small fan moving air past the room temperature thermistor is dirty
Fix: here
Water valves defective:
Symptoms:
Winter time you freeze or in summer you cook. Either way its time to check the water valves.
System description:
This system is rather basic and should be easy to repair.
The two main problems are 1) the solenoids are jammed or
2) the control signal is wrong.
The water valves have one water input (from the engine) and two outputs
(to left and right side heater cores inside the cabin).
The IHKA sends a control signal to drive each solenoid of each valve.
When the control signal is OFF, the solenoid lifts and water flows through the heater core
When the control signal is ON,
the solenoid drives the valve down to stop the water flow.
Here is what to look for.
With
power ON (ignition switch in position I or II) & temperature set to maximum (28 deg C), the control signal should be 0 V.
At
temperatures under 28 deg C but above 16 deg C, the signal is
pulsed: the control period increases as the temperature is lowered.
At the temperature setting of 16 deg C,
the solenoid is driven fully closed: the control signal is steady 12V.
Check the control signal
by using this type of impulse meter
Digital multimeters (DMM) are limited, as they always show only the middle/average value.
At
max. 28 degree C. the light should be fully/always off, at 16 degree C
minimum temperature the light should be fully on. In between 16 and 28
degrees, the light should blink, but at different intervals depending
on the adjustment. Best is to switch the blower fan to max also, as
otherwise the heater valves are adjusted automatically by the system,
and the blinking frequency is reduced.
Connect the clamp of the test light at the pole of the jump start pole (Plus)
Then
'stick' the needle of the test light into the yellow/brown wire for the
driver side and yellow/purple (violet) wire for the passenger side. The
light will blink according to the impulses or it will be full on at the
16 degree Celsius position, and it will be off at the maxiumum
temperature adjustment of 28 degree Celsius.
If the control
signal is OK, give the solenoids a sharp whack with the plastic handle
of a screwdriver; this may dislodge a stuck valve.
water valve repair is here