Engine Noise, A/C Not Working Right? Check Compressor Clutch First (B11080B)

ENGINE NOISE, A/C NOT WORKING RIGHT? CHECK COMPRESSOR CLUTCH FIRST

TECHNICAL SERVICE BULLETIN

SERVICE INFORMATION

Got a vehicle in your shop because there's an engine noise from the drive belt area, the A/C sometimes doesn't work, or it doesn't work at all? What you might be dealing with is too much clearance (air gap) in the A/C compressor clutch set or worn clutch parts, so don't  replace the whole compressor.

Those symptoms can vary, depending on how bad  the problem is, and for how long  it's been going on. To your service client, if the clutch intermittently slips under acceleration or doesn't engage at higher temperatures, it looks like the A/C isn't doing a good job. And it can take some time before it's even noticed. Heat from the slipping clutch can eventually damage the rotor pulley bearing and the field coil.

To troubleshoot these problems, here are some handy tips:

• Check the PGM-FI Data List  . Hook up the HDS, and go to the PGM-FI Data List.  Scroll down to A/C SWITCH  and A/C CLUTCH.  The A/C SWITCH  signal tells you the control panel is getting the A/C request and trying to supply a ground. The A/C CLUTCH  signal tells you the ECM/PCM is trying to supply a ground for the compressor clutch relay. Keep in mind that circuit problems can keep either of those events from happening. If both values read ON  (green light), the compressor clutch should be engaged. If it's not  engaged, you're probably looking at too much clutch clearance or an open (high-resistance) field coil.
• Pinpoint the noise  . It sounds like a whirring, grinding, scraping, or humming, and might not be noticeable until the engine has been running for a while. You'll usually hear it best with the compressor clutch disengaged. When it engages, the noise changes pitch or goes away.

  To pinpoint that noise, hold the engine speed steady at 2,000 rpm  with a throttle depressor tool. Then, with a mechanic's stethoscope, touch each part that's driven by the accessory drive belt. You'll hear that noise the loudest at the compressor body or the aluminum part of the lines that are bolted to it.

  Before you blame the rotor pulley bearing, make sure the compressor mounting bolts are torqued to spec and the A/C lines aren't  touching the body. Loose bolts or line contact can make a similar noise to the one you're trying to pinpoint.

• Do some initial checks  . To find out if you're dealing with a compressor clutch problem-or something else in the A/C system-first check these items with the compressor in place:
  • Armature plate finish:  Check it for blistering or burning.
  • Field coil:  Measure the resistance, and compare it to the spec in ISIS. If it reads open (infinite resistance) or it's the least bit out of spec, the field coil will need replacing. It's designed to protect the compressor and shaft seal by opening if it overheats.
    NOTE: Since you're working with a low-resistance part, make sure your digital multimeter is zeroed out before  you start, to allow for any resistance in the test leads. For more info on that, go to Online University and check out self-study module ELC31 - How to Measure Resistance  .
• Clutch clearance:  Check it with a feeler gauge, and compare it to the spec in ISIS. Use the long side of the gauge, and slide it into the gap no more than 1/8 inch (3 mm)  . You've got to do that because uneven armature plate wear can mask a clearance problem.

  If the armature plate's finish is damaged, or the measured field coil resistance or clutch clearance is out of spec, you've probably got a clutch problem. At this point, you'll need to remove the compressor for further inspection.

• Check other A/C parts  . Other A/C system problems can lead to compressor clutch problems, so be sure to check for these conditions as part of your troubleshooting:
  • Oil leaking onto the clutch surfaces
  • Too much discharge pressure from compressor clutch relay problems
  • A condenser or radiator fan that's not working
  • One or both fans not turning the right way
  • A dirty, corroded, or damaged condenser
  • An aftermarket condenser

To fix these problems, check out the August '11 ServiceNews  article "A/C Compressor Clutch Inspection and Replacement Tips."