940 1987 heating stops after one hour

[sprokkie]

Hi,

I have an unusal problem with my Volvo940

After one hour driving the heating stops, not really stops it become's colder inside. If i turn the dial for the heating it becomes normal again.

The AC kick's in and out even the switch on the dashboard is set to off. When driving with a cold engine the cooling fan starts running on high after aprox 1-2 minutes and stay's on to long. The engine temp is normal not to cold, the outside temp is aprox 8 degrees here in the Netherlands now. I tried to locate the switch for the coolingfan, but i couldn't find it on the radiator or in the hose. All above starts as a whole problem at once

Anyone any ideas ?

Regards
Sprokkie

 

[James Sweet]

Hi,

I have an unusal problem with my Volvo940

After one hour driving the heating stops, not really stops it become's colder inside. If i turn the dial for the heating it becomes normal again.

The AC kick's in and out even the switch on the dashboard is set to off. When driving with a cold engine the cooling fan starts running on high after aprox 1-2 minutes and stay's on to long. The engine temp is normal not to cold, the outside temp is aprox 8 degrees here in the Netherlands now. I tried to locate the switch for the coolingfan, but i couldn't find it on the radiator or in the hose. All above starts as a whole problem at once

Anyone any ideas ?

Regards
Sprokkie

As I recall, the cooling fan is controlled by the ECU. You may have a bad coolant temperature sensor, this is separate from the one used for the temperature gauge. Not sure why the AC is cycling, you don't have Defrost enabled do you? That will run the AC compressor.

 

[sprokkie]

As I recall, the cooling fan is controlled by the ECU. You may have a bad coolant temperature sensor, this is separate from the one used for the temperature gauge. Not sure why the AC is cycling, you don't have Defrost enabled do you? That will run the AC compressor.

The AC is turned off at the with the dashboard switch.
If the coolant temparature sensor is bad, why does the fan runs at high speed after a minute or two ? when its broken the fan doesn't run or doesn't stop running, but that is my opinion.

Where is the switch located ? how do i test it ?

regards
Sprokkie

 

[James Sweet]

sprokkie wrote:

It depends on how it breaks. A thermistor can fail either open circuit or short circuit, so the ECU could think the engine is either too hot or too cold. Of course the problem may be something else entirely, this is just a guess. The sensor is located in the cylinder head under the intake manifold.

 

[sprokkie]

sprokkie wrote:

It depends on how it breaks. A thermistor can fail either open circuit or short circuit, so the ECU could think the engine is either too hot or too cold. Of course the problem may be something else entirely, this is just a guess. The sensor is located in the cylinder head under the intake manifold.

Any idea how this affects the heating inside the car ?
Is the fan running on high cooling to much so the heater for the car gets colder ?

 

[James Sweet]

sprokkie wrote:

Could it be because the AC is kicking in?

How's the coolant level in the car anyway?

 

[sprokkie]

sprokkie wrote:

Could it be because the AC is kicking in?

How's the coolant level in the car anyway?

Coolant level 4mm under max, that ok for me