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AC Pressure Rises at Idle = Compressor Shut Off

 
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  • 4 Post By LionPT
  • 2 Post By Azrak
  • 3 Post By PTCrews

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Old 22 Jul 2017, 08:42 am
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Join Date: Apr 2016
Location: Chicago
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Default AC Pressure Rises at Idle = Compressor Shut Off

Hello All,

I have replaced several components on the PT (compressor, a hose, dryer, etc.), to resolve leaks.

After evacuating the system, it holds a vacuum. After several attempts to charge the system, the low side pressure starts fluctuate; going as high as 90 psi. Once that starts, the compressor would shut off and the pressure starts to drop. The compressor would turn on at about 50 psi and then shut off again at about 70 psi (I will get the exact numbers soon).

I noticed that when the fan kicks on, it seems to be OK at idle.

Is the a sensor related to the fan bad or something? Or is the system simply overcharged?

Thank you in advance for you help!
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Old 22 Jul 2017, 11:01 am
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Default Re: AC Pressure Rises at Idle = Compressor Shut Off

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Originally Posted by PTCrews View Post
Hello All,

I have replaced several components on the PT (compressor, a hose, dryer, etc.), to resolve leaks.

After evacuating the system, it holds a vacuum. After several attempts to charge the system, the low side pressure starts fluctuate; going as high as 90 psi. Once that starts, the compressor would shut off and the pressure starts to drop. The compressor would turn on at about 50 psi and then shut off again at about 70 psi (I will get the exact numbers soon).

I noticed that when the fan kicks on, it seems to be OK at idle.

Is the a sensor related to the fan bad or something? Or is the system simply overcharged?

Thank you in advance for you help!

The fan should be on at all times while the A/C is running.
Either 1 of the 2 fan relays is bad or 1 of the 2 fan speeds is broken.
Check the relays, then check or replace fan.
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Old 22 Jul 2017, 07:44 pm
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Default Re: AC Pressure Rises at Idle = Compressor Shut Off

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Originally Posted by LionPT View Post
The fan should be on at all times while the A/C is running.
Either 1 of the 2 fan relays is bad or 1 of the 2 fan speeds is broken.
Check the relays, then check or replace fan.
+1
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Old 22 Jul 2017, 10:43 pm
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Default Re: AC Pressure Rises at Idle = Compressor Shut Off

Thanks LionPT and Handy! I will keep you posted.

Thanks again!
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Old 24 Jul 2017, 11:30 am
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Default Re: AC Pressure Rises at Idle = Compressor Shut Off

I will try to swap the fan relays tonight and see if there is a difference.

Meanwhile, here is a little more detail:

Pressure before connecting the gauge to the car. Note: There is a can of refrigerant attached but all valves are closed.



Pressure after connecting the low side only. Note: Engine not running



Pressure after starting the car.



Video of pressure after the car ran for a couple of minutes. The compressor is cycling on and off; I assume the high pressure switch shuts the compressor off. Note: The fan never turned on.
Compressor Cycling On and Off


Pressure after shutting engine off.
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Old 24 Jul 2017, 12:57 pm
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Default Re: AC Pressure Rises at Idle = Compressor Shut Off

Pictures posted on photobucket are less than worthless.
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Old 24 Jul 2017, 02:22 pm
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Default Re: AC Pressure Rises at Idle = Compressor Shut Off

Quote:
Originally Posted by Azrak View Post
Pictures posted on photobucket are less than worthless.
What are you guys using to post and share?
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Old 24 Jul 2017, 03:08 pm
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Default Re: AC Pressure Rises at Idle = Compressor Shut Off

I use imgbox. Very simple, but limited in features. At least it's free. Others use imgur. Do a web search on 3rd party image hosting option.

Highest probability of non-working fan is worn brushes. The simple fix for that is a new fan. Relays rarely go bad but testing them out by swapping costs nothing so that's a good start.
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Old 29 Jul 2017, 08:44 am
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Default Re: AC Pressure Rises at Idle = Compressor Shut Off

The low speed on the fan wasn't working.

I wanted get a Chrysler fan, but didn't want to spend almost $300.

I picked one up for under $100 with a lifetime warranty.

Problem solved! Thank you all for your help.
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