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John, triple chrysler master tech
Category: Chrysler
Satisfied Customers: 2251
Experience:  43 years,triple chrys ,ase master tech,l1,t2 b5 a1-a8 Hev spec.
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pt cruiser....when a/c is switched on, cooling fan does not

Resolved Question:

pt cruiser....when a/c is switched on, cooling fan does not operate. What is your diagnosis?
Submitted: 7 years ago.
Category: Chrysler
Expert:  John replied 7 years ago.
Hi my name is john

What year is your PT?

Do you have tubro?
Customer: replied 7 years ago.
It is a 2003 pt without turbo
Expert:  John replied 7 years ago.
If you cycle the key ON OFF ON OFF ON with in 5 seconds and look at the display is there a P code number on cluster.
Customer: replied 7 years ago.
there is no P codes on the cluster. I also used a scanner and no codes came up. It is my undersanding when you switch thea/c control on the cooling fan should come on to cool the condenser but this is not happening. Since the fan is not on, the freon actually seems to boil in the condenser causing the compressor to cycle and excessive low side pressure because of the condenser not being cooled down
Expert:  John replied 7 years ago.
Your right about that.

there is fuse 12 on the inside fuse box that control both fans

than there is two relay in the outside fuse box the control high and low fans.

and two relay for this system.

If you have 12 volt here than check the relay for power at pins 25 on the low relay should be hot with the key on and pin 4 on the high relay should be hot with the key on.


Expert:  John replied 7 years ago.
You will need a volt ohm meter for the tests.

Check fuse 5 under the hood also.

Customer: replied 7 years ago.
fuse 12 on the inside fuse box is good. outside fuse box pin #4 and 5 have power for high speed radiator fan relay. pin #25 and 28 have power for low speed. I have exchanged the relays and they are not considered possibilities. I am leaning toward the coolant temperature sensor. Am I headed in the right direction?
The funny thing about this is if you let the car run to operating temperature the cooling fan comes on and off automatically as needed, but will not control when a/c switch is on. I even took the dash a/c switch apart, cleaned it, and the contacts, so I know it is working properly. Please help!!!
Expert:  John replied 7 years ago.
Non Turbo Fan Opertion: Radiator fan operation is control by the Powertrain Control Module (PCM) with inputs from the temperature of the coolant, which is sensed by the coolant temperature sensor, and vehicle speed which is measured by the vehicle speed sensor. The PCM turns on the fan through either the high or low speed fan relay. The PCM provides a ground to the relay's control circuit.

To control radiator fan operation, the PCM looks at inputs from:
? Engine coolant temperature
? A/C pressure transducer (turbo only)
? Ambient temperature
? Vehicle speed
? Transmission oil temperature (automatic transmission only)

A/C High Pressure Switch Operation:
The A/C high pressure switch is located on the rear of the A/C compressor. The A/C high pressure switch turns off the compressor if the refrigerant system pressure exceeds 3240 kPa (470 psi). The A/C high pressure switch is factory calibrated and cannot be adjusted or repaired and, if faulty or damaged, must be replaced.

A/C Low Pressure Switch Operation:
The A/C low pressure switch is electrically connected in series with the A/C-heater control mode switch and the A/C high pressure switch, between ground and the powertrain control module (PCM). The A/C low pressure switch contact opens or closes the path the ground, signaling the PCM to turn the A/C compressor clutch on and off. This regulates the refrigerant system pressure and controls evaporator coil temperature. Controlling the evaporator temperature prevents condensate water on the evaporator fins from freezing and obstructing air conditioning system air flow.
The A/C low pressure switch contacts are open when the suction pressure is approximately 152 kPa (22 psi) or lower. The switch contacts will close when the suction pressure rises to approximately 234 to 262 kPa (34 to 38 psi) or above. Lower ambient temperatures, below approximately -1° C (30° F), will also cause the switch contacts to open. This is due to the pressure/temperature relationship of the refrigerant in the system

It could be the temp sensor for this,
Customer: replied 7 years ago.
you may agree with the coolant temperature sensor because my understanding is that it is over ridden by the a/c on switch. Does this make sense? Something I am wondering about since this has a 2 speed cooling fan, could low speed be burned out and high still work? If so, what controls the speeds?
Expert:  John replied 7 years ago.
The ac control head does for non tubro and the ac tranducer does for tubro models.

you could put 12 volts to the raditor fan motor on the high side and see if it will run.

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