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I have 2011 Mazda CX7. When I first turn the car on I can see the A/C clutch being engaged, but after the car runs for bit, then clutch disengages. After a while it starts to engage for few seconds and than back off for about 10-15.

While A/C clutch is engaged, pressure gauge shows it to be on bottom side of green.

I have followed direction on bottle of A/C Pro to fill my unit. But it have not made any difference. It seems that sometimes it decides to start blowing slightly colder air while other times it just blows hot air.

Update:

After taking it to Pep Boy's for diagnostics. It turned out to be a relay. Once relay was repaired it turned out that I overcharged the system. Now I taking it to service for evac and recharge. In the end $49 for diagnosis, $60 for evac and recharge, $40 for bottle of A/C pro. In the end I feel lucky to get system repaired for under $200. If I took it to get it diagnosed in the first place it would have cost me whole lot less.

Lesson Learned: Do not charge system unless you have a gauge to read both LOW and HIGH pressure. Next time before I waste money on charging system I will buy the following gauge http://www.harborfreight.com/a-c-manifold-gauge-set-92649.html

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    One possible reason for the clutch to disengage like that is to protect the compressor from surging. How confident are you that the amount of refrigerant in the system is correct? How much pressure are you seeing on the high side?
    – Zaid
    Commented Jul 26, 2014 at 19:34
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    Usually when I fill A/C units, I like them to be at least to the mid-line if not 3/4 of the way to the top of the green area (around 40psi) when the clutch is engaged. This allows the A/C to function well, yet not put too much pressure on the system. I've seen it where the low end pressure will do exactly as you are saying, both in not cooling very well and with the cycling of the clutch.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jul 27, 2014 at 9:53
  • When I started the car and clutch was engaged it showed around 25psi at about 75 degrees Fahrenheit.
    – Vladimir Oselsky
    Commented Jul 27, 2014 at 17:15
  • Well, 25 psi would be considered low for most applications. It should be around 50-60 psi at steady state (when the A/C has been running for some time)
    – Zaid
    Commented Jul 28, 2014 at 4:23

1 Answer 1

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Your description points to a gas leak, or a control electronics fault. You need to have your AirCon system checked over and possibly re-charged by a service quality machine. The AirCon can switch itself on and off intermitantly when you have a faulty resistor pack/thermostat, faulty track on your Accelerator position switch, faulty Hot-Cold control, faulty system pressure switches, compressor clutch, or associated relays and wiring. The way to go is an AirCon system scan to isolate the electrical fault(s).

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  • I plan on taking it to service center to get it diagnosed tomorrow. Will post results.
    – Vladimir Oselsky
    Commented Jul 27, 2014 at 17:16
  • Turned out to relay issue and improperly filled system. In the end it had too much pressure instead of too little. If it was not for bad relay it would cause more damage.
    – Vladimir Oselsky
    Commented May 12, 2015 at 11:34

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