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post #1 of (permalink) Old 06-04-2019 Thread Starter
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A/C Problem.

07 A/C went out about 5 months ago. Finally got around to putting a new clutch on it and now it works, the only issue is that once it’s on if you turn it off you can’t turn it back on. If you turn the car off for a while then it will work again.
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post #2 of (permalink) Old 06-04-2019
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Originally Posted by cmurray View Post
07 A/C went out about 5 months ago. Finally got around to putting a new clutch on it and now it works, the only issue is that once its on if you turn it off you cant turn it back on. If you turn the car off for a while then it will work again.
You may be low on refrigerant (freon). IIRC, there's a low side switch on the hose from the evaporator. When you first turn on the system, the low side and high side are at the same pressure - they are equalized. But after the system has run for a while, the high side is at a much high pressure, around 200psi, IIRC, while the low side is around 40-50psi.

If your system is low on refrigerant, the low side may drop so low that the low side switch is preventing the system from starting up again after it's been shut off. (At least, that's my theory ) Letting it sit for a while allows the two sides to equalize thereby raising the low side pressure enough to allow the compressor to engage next time the AC is turned on.

Per my manual:

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high or low pressure condition exists. The powertrain control module (PCM) disables the compressor clutch under the following conditions:

A/C pressure is more than 3034 kPa (440 psi). The clutch will be enabled after the pressure decreases to less than 2068 kPa (300 psi).

A/C pressure is less than 241 kPa (35 psi). The clutch will be enabled after the pressure increases to more than 248 kPa (36 psi).

Another possibility is that, once the system is running, the high pressure goes up too high thereby preventing it from running once it's been turned off. As before, shutting the car off for a while would allow the high side pressure to drop back down below the max limit value.

Most likely, it's a low side issue - it's a 12 year old car - they lose freon, not gain it Seriously, unless someone has recently charged the system, it's probably a low pressure issue rather than a high.

You might try charging the system to see if the problem goes away.

Or get a set of gauges hooked up to it and see what the pressures get to after the AC has been running for a few minutes.

HTH.

Doug

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Thanks, I’ll put gauges on it and go from there.
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Did you set the air gap after installing the clutch? When the compressor won't re-engage, carefully tap the faceplate with a screwdriver handle, broomstick, etc. to see if it will pull in.
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post #5 of (permalink) Old 06-05-2019 Thread Starter
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I’ll give that a try too. Anything to avoid taking it to going to the shop.
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Originally Posted by cmurray View Post
I’ll give that a try too. Anything to avoid taking it to going to the shop.
You might pursue the compressor clutch idea first. It's probably easier to check. If you can get a voltmeter on the wires to the clutch, you can:

  1. Check the voltage when it's set to OFF and not running (should be no voltage)
  2. Check the voltage when it's set to ON and running (s/b +12V)
  3. Check the voltage when it's set to ON and not running (??)

If the voltage in item 3 matches item 2 (+12V), that indicates the engine computer is instructing the clutch to engage but it's not doing it, indicating a clutch issue. Conversely, if it matches the voltage in item 1 (0v), then put some gauges on it on the AC hoses.

One more thought: You can also probe the relay for the AC compressor. It's in the underhood fuse block. Connector C1-pin C1 will be low (~0v) when the compressor is supposed to be engaged, high (~+12v) otherwise. Connector C1-pin D1 will be high when the compressor is supposed to be engaged, low otherwise. The ECM controls the relay which in turn controls the compressor. I've attached a drawing. (Connector C1-pin D1 feeds the dark green wire, D-GN, to the compressor.)

There's also a 10A fuse downstream of the relay. You might pull that out and inspect it, or swap it for another.

HTH.

Doug

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If your socket set is all the same brand, you might be a city slicker.

.
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post #7 of (permalink) Old 06-10-2019 Thread Starter
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Quote:
Originally Posted by plano-doug View Post
Quote:
Originally Posted by cmurray View Post
I’ll give that a try too. Anything to avoid taking it to going to the shop.
You might pursue the compressor clutch idea first. It's probably easier to check. If you can get a voltmeter on the wires to the clutch, you can:

  1. Check the voltage when it's set to OFF and not running (should be no voltage)
  2. Check the voltage when it's set to ON and running (s/b +12V)
  3. Check the voltage when it's set to ON and not running (??)

If the voltage in item 3 matches item 2 (+12V), that indicates the engine computer is instructing the clutch to engage but it's not doing it, indicating a clutch issue. Conversely, if it matches the voltage in item 1 (0v), then put some gauges on it on the AC hoses.

One more thought: You can also probe the relay for the AC compressor. It's in the underhood fuse block. Connector C1-pin C1 will be low (~0v) when the compressor is supposed to be engaged, high (~+12v) otherwise. Connector C1-pin D1 will be high when the compressor is supposed to be engaged, low otherwise. The ECM controls the relay which in turn controls the compressor. I've attached a drawing. (Connector C1-pin D1 feeds the dark green wire, D-GN, to the compressor.)

There's also a 10A fuse downstream of the relay. You might pull that out and inspect it, or swap it for another.

HTH.

Doug

.
Tapped on the clutch and it turned on. Do you know the torque specs on the clutch bolt by any chance? I may have it too tight. If not I need to remove shims correct? Pressures were fine btw.
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post #8 of (permalink) Old 06-10-2019
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Originally Posted by cmurray View Post
Tapped on the clutch and it turned on. Do you know the torque specs on the clutch bolt by any chance? I may have it too tight. If not I need to remove shims correct? Pressures were fine btw.
According to my manual, the torque spec is 106 in-pounds (12 Nm).

I've never torn into the clutch nor compressor, so I can't be much help there. I pdf'd the clutch replacement instructions from my manual. They are attached.

Getting that thing properly lined up looks a bit tedious - a special tool is supposed to be used - J 37872 Compressor Clutch Holding Tool .

At a glance, it appears Sheila nailed it, that you may need to adjust the shims. Air gap should be 0.3-0.6 mm (0.012-0.024 in).

HTH.

Doug

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File Type: pdf compressor_cl;utch_2007_impala.pdf (1.32 MB, 4 views)

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If your socket set is all the same brand, you might be a city slicker.

.
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post #9 of (permalink) Old 06-10-2019
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^+1. Try removing shim(s). Sorry, dunno the torque spec.
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