944 86 ac problem only cold air

[kmakovac]

Hi

today my car don't want to heat untill i depress the "defrost switch".So with the switch on it heats full witout problem.The temperature knob doesn't make any differnce from cold to hot.
Before it works you can heard an audible "click" when it goes from cold to hot and viceversa.Now nothing.

So it blow cold all the time untill i depress the defrost switch.It works fine for years so is a new problem.
Water level ok,heathing valve ok,clip ok...

Any ideas?
Thanks

[GreenWater]

I was going to say check the coolant level. Maybe it is the switch that is bad? I don't know if there is a test for the switch, but there should be a way to find out if the switch is good or not.


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[kmakovac]

So i investigate and conclude this:

-3 sensor with ommeter OK
-replace the interior sensor with motor but nothing
-the outer vacuum/water valve closes in all position of temp-knob
-the outer vacuum/water valve open in defrost position

So what control the selenoid valve in engine compartment?It's operet by vacuum but i can't uderstand why it's work in defrost position and closed in all other?

Any ideas?(water,termostat and all global thing OK)

[kmakovac]

so after 2/3 hours on +2°C out i resolve the problem:

- i change all the temp.sensor-nothing
-change the ventilator cabine module/gauge-nothing
-try the vakuum valve-engine compartment-OK

so i seet 10 min and try to understand:
when you press the defrost switch everything work fine,the vaccum valve open and heating works fine.This situation bypass all the sensors and force full heating.
In global heating works,so the problems is in the sensors or comand.
hange the sensores,measure it and all OK.
Problem with the AC module?Change it and nothing.

What remain?Cables,shorts.

I try to make better conections on plugs with a little screwdriver and WD-40 and everything turn to normal!!!

So the issue was been lost of contacts in the plug"A" to modul,maybe for my 18" wheels....

Interesting Gremlin....

[GreenWater]

Good information to know. Bad connection gremlin.


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[kmakovac]

i look deeper in the electric diagram of the AC of 944 and if you see the 3 temperature sensosr have the same ground and tecnical is very easy to lost it with trouble in information to heating control module.

maybe i will put a new ground on one or more sensors if the problem return.

[GreenWater]

kmakovac -

What wires did you clean so they would contact better? I think a bad connection could be my problem as well. My heater is different everytime I drive the car. One time 27deg is super hot and the next time 27deg is only warm.


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[Along4ride]

Have you checked the three air flap servos for proper operation? I forget exactly how air is piped around in the HVAC, but If one or more flaps where malfunctioning you might have an issue that that. Pushing the defrost button puts the servos in a specific mode which could explain why you get heat.

Just a thought...