Intermittent A/C - suggestions?

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  #1  
Old 05-01-12, 12:29 PM
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Intermittent A/C - suggestions?

Vehicle is a 2001 Jeep Cherokee. When it works, the A/C cools very well, but the compressor periodically disengages. I've checked the low side pressure and it is in the normal range (just over 40# at 85F). There doesn't seem to be a pattern, except it "seems" to happen more often when I've been cruising in traffic, and then stop at a light. It appears to kick out more often then, but it has also happened at highway speeds.

From what I've seen on troubleshooting charts, it could be the low pressure cutout switch, or it could be the thermostat. I've only had this vehicle a few weeks, so I don't know the history - how long this has been happening, etc.

Is this an obvious symptom of something, or does anyone have a suggested troubleshooting procedure to eliminate a possible problem?

Thanks.
 
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Old 05-01-12, 02:26 PM
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1. compressor is supposed to engage/disengage
2. overall, how does a/c work?
3. how do you know it's disengaging more frequently?
4. do you have automatic climate control?
5. what temp switch you talking about?
6. it should engage at long stops more often, as you do not have air flow assistance, coming from moving at any/higher speeds.
 
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Old 05-01-12, 03:31 PM
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1. compressor is supposed to engage/disengage
Yes, understood. It disengages and stays disengaged, and temp coming out of vents (of course) rises.
2. overall, how does a/c work?
56F temp out of center vent at idle, 83F ambient. That is when the compressor is engaged, of course.
3. how do you know it's disengaging more frequently?
See (1) above - temp from vents continues to rise, at which point I pull into a parking lot, open the hood and see that the compressor is not engaged.
4. do you have automatic climate control?
Manual
5. what temp switch you talking about?
I didn't mention a temp switch, mentioned low pressure cutout switch and thermostat. By thermostat, I'm referring to the temperature control dial, which should control the frequency of engage/disengage of the clutch, right?
6. it should engage at long stops more often, as you do not have air flow assistance, coming from moving at any/higher speeds.
Yes, but in this case I'm saying it kicks out & doesn't kick back in to provide a continuous flow of cold air.

I will say I'm a little confused on exactly what pressure the low side should be at 80 - 85F. I see one chart which says up to 40# but another which says up to 56#. Any input on what that should be? I may still be too low on R134, which would cause the compressor to kick out on low pressure.

Read more: http://www.doityourself.com/forum/pa...#ixzz1tevU64wW
 
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Old 05-01-12, 03:35 PM
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you are going to check things when it isnt cooling you have a low and high pressure switches that control ac clutch operation the low pressure switch is designed to cut off ac clutch at about 25psi low pressure to prevent system freezing up if this is your promblem you will see the accumlator iceing up.the high pressure switch switch will cut out ac clutch at about 300psi high pressure check and see if cooling fan motor is coming on if it isnt working the ac condensor will overheat causing excessive high side pressure, cherokee also had intermittent ac clutch engagement due to a weak compressor coil if clutch wont engage and you have 12 volts and ground at the compressor connector smack the compreesor clutch to see if it reengauges.
 
  #5  
Old 05-02-12, 06:01 AM
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Auxiliary cooling fan is working as it should. I'll carry a rubber hammer for a couple of days to see if "persuasion" gets the clutch to engage.

Thanks.
 
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Old 05-02-12, 05:11 PM
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Perhaps it's a flaky a/c relay.
 
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Old 05-02-12, 07:18 PM
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Yes, my apologies. It was "thermostat", not "temp switch". Still a mystery, what t-stat has to do with this.
There's a standard on how a/c is supposed to work. I think it's 20 degrees below ambient? Anyone correct this, as I am shooting off bad memory.
Do you have a small visor in a/c line, showing freon flow? look at it. If it's grey and bubbly, you are low on freon/oil mix. If it's nice steady and clear - you are good on freon mix, and problem is somewhere else.
Try simple - disconnecting pressure switch plug and cleaning it with electrical parts cleaner.
The way you have it described sounds like climate control unit issue. That's why I asked about automatic control.
 
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Old 05-03-12, 03:12 PM
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The problem appears to be in the selector switch on the dash. There are 3 settings for Air Conditioning:
-Dash vents
-Dash vents plus Floor
-Max (Recirculate)

I had been using the normal Dash Vent setting, but I discovered today that when set in either Max or Dash plus Floor, the compressor does not disengage and fail to re-engage as it does in the Dash Vent setting. In either of the other two settings, it works just great and cools well.

Hopefully, this resolves the question, and it is just a matter of either putting in a new dash selector switch or just using one of the other two settings.

Thanks for the advice, and maybe this will help someone else as well.
 
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