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95 volvo high head pressure

jesaire on Fri May 16, 2008 4:09 PM User is offline

Year: 95
Make: volvo
Model: 850 wagon
Engine Size: 2.4
Refrigerant Type: 134a
Country of Origin: United States

Colleagues,
I am asking if one of you can give me some info on my volvo? I am witnessing my a/c system shutting off when driving on days when the osa ambient is >100 degrees.
My request is can one of you guy/gals give me info on my condenser fan for this car? that is, should the condenser fan turn on once the a/c is enabled or does it cycle on press/temp.

jesaire
hot in So Cal..

bohica2xo on Sat May 17, 2008 3:01 AM User is offline

You have a 2 speed fan on that 850, and it is controlled by the powertrain module on the RH side of the engine bay.

The Fan relay itself in mounted at the top passenger side of the fan shroud. The red & green wires go to the fan for high & low speeds. The module selects a fan speed based on engine temperature, road speed & the high pressure switch on the high side line. You should see low speed fan operation as soon as the compressor starts if you are stopped.

The fan should run at low speed if the vehicle speed is under 40 mph with the A/C on, even with a cold engine. The fan will only step up to high speed if the A/C is on & the coolant temperature goes over 240f.

It sounds like you are cycling on the high pressure switch, with no fan operation. Check the fan motor first. Pull the connector from the relay, and feed the motor directly. If it runs, you may have a bad fan relay. There is no fuse to check on the high current side of the relay, it is fed with a fusible link that is hot at all times. Check the fat red wire for +12 volts, this is the power from the battery.

B.



-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

jesaire on Sun May 18, 2008 4:57 PM User is offline

Bohica,
Thanks for the info, You are a great contribution to this forum. I will post my results with my repairs.

Thank You

Jesaire

So Cal

jesaire on Sun May 18, 2008 6:13 PM User is offline

Bohica,
I had a chance to trouble shoot the system here is what I found:
The fan lo & high fan speed work fine when powered directly ( bypassing the relay) when I start the car with the a/c on Low speed fan starts ( system ok). I used a 12 volt test light for my test instrument on the fan relay. here is what I found:

Car running at Idle: osa ambient 100 degrees ( one hot weekend !!)
first reading: grnd to Red wire to relay _ hot.
second reading: grnd to low speed_ hot.
Third reading: grnd tp high speed_ hot.
Fourth reading: relay coil wire (yellow) No power.
Fifth reading: relay coil wire ( yellow w/ white stripe) No power, but... relay pulled, and high speed fan came on.

Can you possibly forward some advise on what component failed, Do I have a bad ground on the relay coil?

Many thanks

Jesaire

So Cal

bohica2xo on Sun May 18, 2008 7:32 PM User is offline

Jesaire:

The two coils in that relay are both powered from the red wire - they are always "hot". The PCM controls the relay coils by providing a ground path.

The yellow wire switches the red output wire when grounded. The yellow/white wire switches the green output wire when grounded.

Based on that, I would say your test lamp passes enough current to pull up the relay coil, and the high speed fan. You say that the low speed fan operates when you turn the A/C on, so it looks like your fan control is in order.

To go any farther, you really need system pressures. You may have high head pressures from a blockage, overcharge, etc. Or your condensor may be plugged up on the airside.

How does the system perform at highway speeds?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Edited: Sun May 18, 2008 at 7:34 PM by bohica2xo

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