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A/C clutch intermittent, then not working

Old 05-02-2008, 03:48 PM
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Join Date: May 2008
Location: United States
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Hey all, just joined in order to help solve my friend's A/C problem. I know what a big help forums can be when it comes to a specific car and mechanical issues.

Well i'll get right to it. She has no A/C. When everything is set to max on the A/C, and the car is first started, the clutch will turn on for a second, turn off, and repeat the process about 5 times over the course of 10 seconds, before turning off and remaining off. What could be causing this problem? With a can of refrigerant hooked up to the lowside, with a guage, the reading was high, about 80 or so. When the car is first started and the clutch is cycling, the pressure is in a good normal reading like. When the clutch kicks in the pressure drops severely, below 20 or so.

My theory is that the system is low on charge, and so when the clutch kicks in the pressure on the low side drops so much that it kicks back off. The pressure is allowed to build up so it turns on, but the A/C lowers the pressure so much that it kicks off again.

If that were the case though I don't see how the clutch would remain off after a few rounds of that, wouldn't the process keep repeating?

What switches does this vehicle have for the clutch, and where are they? For instance lowside pressure sensor... etc. I can check those for continuity at least and narrow the problem.

The car is a '96 Mercury Cougar. AC has not worked for a few years.

Thanks in advance for any suggestions!

Old 07-01-2008, 01:18 AM
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Join Date: Jun 2008
Location: United States
Posts: 13

This is common. TheHVAC controler is seeing a low charge state and turning the A/C relay off. It cycles for a few times and when the readings are consistant with a low charge it disengeges the clutch until the next key start. Your pressures should be about 25-30 low side and 225-275 hi side depending on outside temps. The low perssure switch cuts out at somewhere like 20 psi or so which kicks off the a/c clutch. Also make sure that your electric fans are working and that nothing is blocking the condencer as this will adversely change your hi side readings.
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