need help with a/c ???

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  #1  
Old 05-25-12, 08:45 AM
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need help with a/c ???

I bought my teenage son a small 2003 chevy malibu a couple months ago, it was cold so did'nt need a/c but it was checked and was working. Now it gets hot and he tells me its blowing warm air. I checked all fuses inside and under hood and all are good. Even switched some of the larger relays with the one that controls the compressor. But clutch is not engaging when a/c button is pressed although the light on the button comes on. There is no voltage on the wires going to the compressor clutch. I just figured if it were low on freon the low side switch would prevent the clutch from engaging. I ran hot wire from battery to clutch and it engages. The only gauge i have, came on a short hose with a can of freon that i bought several years ago and can use the hose to add freon when i need to. I hooked the gauge to the L-p port with the clutch hot wired and cranked the car, then checked pressure and it was almost in the red area and was still moving up. I ran around to turn the car off but before i could switch it off there was a sudden release of pressure and sort of like a fog in the air around the engine. I haven't tried running the compressor again but i did release some of the pressure by pressing the neddle on Low side port. When i hook the gauge back up there is still about 25 lbs showing with the car not running after a week, so it appears to not be leaking down. Now what i'm wondering is if i damaged anything and where did the pressure release from? (the high pressure switch i assume) I just hope i did'nt blow any seals, but if i did it looks like it would have lost all pressure. Appreciate any help with this, and sorry for such a long description.
 
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Old 05-27-12, 02:42 PM
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I think this is why couple yrs ago most of a/c questions here were advised NOT to be answered. Apparently it changed, but this is typical example of how much ecological damage and damage to one who tries to do this can be done.
1. any car blows cold air when a/c is checked out winter time. daahh
2. a/c is supposed to be turned on periodically, or freon/oil mix gums up connections
3. if you have known good system pressure, a/c comp works off jumper, you either have bad pressure switch, or loose contact, or your climate control unit is not working. light comes up means squat.
 
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Old 05-28-12, 03:14 PM
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Came across an odd one last week........First off........YOU don't turn the A/C on.........You ask the ECM to turn the A/C on ...........First the signal goes to the BCM which checks pressure at switches AND (Here's where it gets weird) signal from the intake air sensor......If everything is OK the BCM tells the ECM to drop ground to the compressor relay AND the cooling fan relays......... I had an intermittent intake air and the compressor would cycle with the read from the intake air sensor.......and NO it didn't set a code
 
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Old 05-29-12, 03:38 PM
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When you jumped your switch you bypassed all systems that control ac clutch including your electric radiator cooling fan which also cools ac condensor,without cooling fan high side pressure will just keep climbing and will discharge to prevent ac compressor damage that's the cloud of freon you saw.your low and high side pressure readings with engine not running should read almost ambient outside temperature. First make sure proper freon level.then you might have to use a scan tool to determine all sensor readings sounds like possible sensor problem not letting clutch operation
 
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Old 05-30-12, 12:06 PM
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thanks jktune for the information, have you got any idea which sensor. I have a cheap ob2 scanner that i picked up at harbor freight but it don't do much detailed scanning. BTW ukrbyk, it was in the winter that i checked the a/c but that day was in the high 70's. The only reason i jumped the compressor was to verify that the clutch was working. But this all happened in less than a minute, before i could turn the car off. Just looking for some diagnostic help. thanks
 
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Old 05-30-12, 03:49 PM
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dont think your scanner will access ac sensors.Find your low pressure sensor most of the time is a two wire connector and sensor is in the low pressure line.With the ac switch on and engine running use a jumper wire across the two terminals in the lowpressure switch. If compressor engages you are either low on freon or bad low pressure sensor.
 
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Old 05-30-12, 06:56 PM
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I can't find a sensor on the low pressure line . The only one i see is at the top left side, line from condensor on the high pressure line. I did find this after doing some searching, although this car is a 2003 malibu it must be the same........................................... (There is no low pressure cutout switch on the 1997-2001 Chevrolet Malibu. This holds true for both L4 cyl and V6 cyl models of this regardless of two door or four door. There also is not a high pressure cutout switch, but there is a pressure switch on the high side line at the top of the condensor, on the aluminum line coming from the condensor to the A/C compressor. Most parts stores will find it listed as a high pressure switch, but it actually is a transducer switch that works off the high pressure side. The compressor clutch engage and disengage functions are controlled by the on-board computer. It sends a 5 volt reference signal to the pressure transducer switch and the switch modulates the return voltage back to the on-board computer. The on-board computer reads that voltage change and determines if the high side pressure is within a certain range. If it is below that range then the on-board computer grounds the A/C clutch relay in the relay/fuse box on the driver-side under the hood, which in turn puts 12 volts to the A/C clutch engaging the compressor. Once the high side pressure reaches a certain point and the voltage return from the pressure transducer switch to the on-board computer is above a certain range, then the on-board computer removes the ground from the A/C clutch relay, which removes the 12 volts to the A/C clutch and it disengages.
This particular system of controlling the A/C clutch/compressor cycling is used on many of the vehicles GM has been building since 1994. The set up of the system varies from vehicle to vehicle, but almost all of them control the compressor from a switch used on the high side pressure line)..........I have 5 volts at the connector
 
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Old 05-31-12, 07:30 PM
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no worries, I jumped compressors before, and not once. As a result, I also fried - and not just one. Good part is, you can easily resuscitate it on a bench, with a little bit of elbow grease and good oil.
 
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Old 06-04-12, 03:29 PM
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Looked up wiring diagram on all data .AC control head sends a a ac request to bcm then sends to pcm ,ac transducer 5 volt reference on gray wire should have voltage on pin c red/blk wire at 220 psi will be 5 volts,voltage will vary depending on pressure and voltage on pin a blk wire at 30 psi will be 0 volts these are pressure inputs to pcm then pcm grounds pin 39 c2 connector of pcm dkgrn/wht wire to ac relay. Fuse 37 10 amp feeds ac compressor clutch relay then sends power to ac compressor dk/grn wire to turn on compressor.
 
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Old 06-05-12, 07:06 AM
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i replaced the temp sensor that turns the coolant fans on because they did.nt seem to be coming on even after the engine ideled for 10 to 15 minutes in 90 degree heat. They do come on now after about 10 minutes since replacing the sensor. But still nothing with the a/c,when i turn on the switch, i will check that fuse 37. In the fuse box the # 16 relay is listed as for clutch relay. I did check the voltage at the transducer connector with car running and a/c switch on and it shows the 5 volts.
 
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Old 06-05-12, 04:12 PM
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Dont forget to check voltages on all three transducer wires.Do yo have access to a scanner to see if pcm is getting a ac request.
 
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Old 06-05-12, 07:15 PM
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fuse 37 is good. the cheap scanner i have won't do that. I wonder if one of the auto stores could do that.
 
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Old 06-06-12, 04:44 AM
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Needs to be one that is capable of reading real-time data and not just stored codes; not sure what the majority of parts places are using. Can't hurt to ask.
 
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