A/C kicks off at 2000 rpm not reset

kev2

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sorry bill I am not following your train of thought..
thinking out loud:
I read it as the RPM is changing, coasting, breaking and then at the LOWER rpm allowing AC to operate again.
That “psst” sound suggests to me at a high pressure blow off - maybe I am wrong any evidence of discharged refrigerant, oil, tracer dye?
I will need to check unless someone knows, if PCM shuts down AC for HIGH pressure will it code?


Does any one know if the part 95018104 is a blow off valve, transducer, or ?
 

billr

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That's why I'm asking the OP to clarify the "slight brake" application. I interpret that to mean a quick tap, like I do to disengage cruise-control when I know way ahead of time to slow down
 

DavidS

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Nick, I thought by auto or manual you were asking about climate control. I can use A/C by setting cabin temperature or I can set fan myself. Apparently, do not understand the manual vs. automatic question.

I do not think that there is any refrigerant release. The A/C worked before repairs no change after recharge of system. I think that if the psst were a release of refrigerant it would be empty by now. It

The slight brake application turns on A/C when car is back down below 2000 rpm and at highway speeds and A/C has not come back on. A very slight tap, will start A/C again.
 

nickb2

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Nick, I thought by auto or manual you were asking about climate control. I can use A/C by setting cabin temperature or I can set fan myself. Apparently, do not understand the manual vs. automatic question.
If you have ambient temperature sensors, you have a automatic climate control. HVAC control head is also different. I am assuming you have auto climate control. An automatic AC will have an inside and outside ambient sensor and a sunload sensor.

Diagnostic procedures and wiring are vastly different from one system to the other.

OEM part # for pressure sensor is 22664328 and is interchangeable with part # 95018104 so we know the shop changed the pressure sensor and not the relief valve.

I am not seeing any correlation schematic wise on how tapping the brakes can trigger the AC clutch.

Here are snapshots of the entire auto AC system wiring, no note whatsoever of a AC brake switch kill signal. So, if the brake switch for some reason triggers the compressor, that is beyond my level of comprehension and I would need a Tech 2 to verify that claim. I left out the door actuator wiring as it does not pertain to your problem.

Screenshot (779).png Screenshot (780).png Screenshot (781).png
 

nickb2

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Until we see what low and high side pressure readings are at idle and under load (example, at 2000rpm), I don't know how we can help you any further.

This link in principal is what a auto climate control should look like for your car.

http://www.ebay.com/itm/Buick-Centu...ash=item1a17106a40:g:JYQAAOSw2zlXhzon&vxp=mtr

This link is for a manual climate control for your car and if your AC control head looks like this, you have a manual AC system.

http://www.ebay.com/itm/99-02-BUICK...m255caf10e7:m:mxOohm6dfmbNAqRSMFXRJVA&vxp=mtr
 

nickb2

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Unless someone more knowledgeable than me in AC systems can confirm my claim. I have never heard of an AC clutch brake switch kill signal.

I did some google search on that, found nothing that can substantiate that claim.

Have a system performance test done.

Here is how to do that. You will need a set of gauges or a HVAC recovery machine to get those readings.

See pdf included in this post.
 

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nickb2

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Read this link for all your needs. Very informative and gives specified PSI readings a normal operating system should have.

All testing should be done with all doors closed and driver window cranked down just a bit.

A temperature probe will also be needed. I have one I can attach to my multimeter. If you don't have one, something like this http://www.ebay.com/itm/Digital-Thermometer-with-remote-sensor-range-58-F-to-158-F-/331637717165

should do the trick.

Link for troubleshooting AC performance with gauges. Some will say that windows up or down does not affect the performance test, but GM specifies all windows closed with driver window down 5-6 inches.;) See page 2 of provided PDF.

http://aircondition.com/tech/questions/82/Troubleshooting-with-Gauges-FAQ
 

kev2

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Ideally Would want vehicle in bay gauges on system, scanner plugged in.. 2000rpm - lets see what we get.
the schematics show wiring but the "logic" portion is not known...ie high eng temp will disable AC.

That has me thinking could the system be seeing something such as - WOT, lost ECT signal, fan circuit issue, or maybe the system is not actually de energizing the system BUT a clutch issue such as wiring to clutch going open -air gap*- other codes in the B or U series?

*Do we know for sure this is a V5

$.02These are the most challenging and learning type of posts.
 

billr

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Follow the suggestions in Matt's reply #20. Not only will you be able to read actual pressures at the engine rpms where A/C is quitting, but if it won't quit when parked, then that is further evidence that the PCM is dropping the A/C because it perceives the car engine is under heavy load.

Nickb2, that function probably is in the PCM software, not wiring. I'm thinking the PCM drops the A/C to reduce load on the engine if the MAP/MAF and rpm are high; and that having the trans in either P or N (or clutch pedal down, for manual) or having the brake pedal down would "abort" the perception that the engine is pulling hard. That kind of operation was kind of common long before EFI, usually just a simple switch triggered by the carb linkage at WOT.
 

nickb2

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Follow the suggestions in Matt's reply #20. Not only will you be able to read actual pressures at the engine rpms where A/C is quitting, but if it won't quit when parked, then that is further evidence that the PCM is dropping the A/C because it perceives the car engine is under heavy load.

Nickb2, that function probably is in the PCM software, not wiring. I'm thinking the PCM drops the A/C to reduce load on the engine if the MAP/MAF and rpm are high; and that having the trans in either P or N (or clutch pedal down, for manual) or having the brake pedal down would "abort" the perception that the engine is pulling hard. That kind of operation was kind of common long before EFI, usually just a simple switch triggered by the carb linkage at WOT.

That makes a whole lot of sense. Thx Bill.
 

DavidS

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Need the pressure readings at the RPM the compressor kicks off. If you rev the engine to 2000 rpm not driving and hold it there . Does the compressor kick off then to ? Or just when driving ?

Just while driving.
 

billr

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Well, I'm back to the ending of my reply #10...

"Live-data could save a lot of guessing here"
 
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