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Help solve this AC mystery.

ARFFAZ

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ARFFAZ Enthusiast

ARFFAZ

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2007 Silverado Classic 1500 LS 4.8

 

When I start my truck and turn the AC to the on position I can hear the clutch attempt to engage but immediately kicks out.

 

If I put the truck in drive the clutch will engage and stay running cooling the truck. If I move the gear selector to neutral the clutch will disengage and attempt to engage every 30 seconds or so like it does in park.

 

I hooked up one of those cheap gauges to check the pressure on low side and getting a 45-50 PSI reading while I am putting the truck in drive to engage the clutch. Currently 107 deg outside while testing.

 

I had my ac checked out back in March at the mechanic said I was only slightly low but nothing that would cause my AC to not work. He added like 3 oz and sent me on my way.

 

I have jumped the low pressure switch when the clutch is attempting to engage and no success.

 

Now when I am driving around town my ac is off and on working seems to do best while I am at idle or cruising around 2000 RPM. I would like like to believe that my system is low but I do not understand why it won't work when I just the low pressure switch.

 

I am thinking there is a electrical problem but I have no idea where to look...? A/C pressure transducer?

 

 

ARFFAZ Enthusiast

ARFFAZ

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Does the alternator only supply power are truck is out into drive initially? Low voltage maybe? just thinking out loud.

ARFFAZ Enthusiast

ARFFAZ

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Ok today I got some gauges and tried to get a reading but could get the compressor to cycle on. I put the garden hose on the front of the compressor for about 35 seconds and got the compressor to finally engage and stay in gauged while I tested the system for about 10-15 minutes. Here are the numbers I got:

 

Outside temp - 118 Deg

Hi side - 165 PSI

Lo side - 40 - 45 PSI over the entire check

Vent temp - 60 Deg

 

Check done at idle parked in in driveway

 

 

Today I had no AC for most of my drive around town. If I was parked in a parking lot I could get it to cool for a little bit but not long. Today I could get my AC to engage in drive, park and neutral.

 

At home the compressor kept short cycling until I sprayed down the compressor.

Dnt Senior Enthusiast

Dnt

Posted
Posted

Here is what I want you to do. Hook up your guages start engine and and turn the AC on max with fan speed on highest setting and leave the doors open. Now post your readings High and Low. If your compressor does not kick in I want you to take a large long handle screwdriver and carefully smack the chit out of the front of the compressor (aim for the clutch). Most likely the clutch has worn and is not pulling in consistently. Once you verify that, we can move forward with a fix.

ARFFAZ Enthusiast

ARFFAZ

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I already got readings see post # 4

 

Not sure what my readings should be but they sounds a little low.

Dnt Senior Enthusiast

Dnt

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Yeah i see all that but it is critical to follow proper protocol to establish proper readings ONE THING I LEFT OUT IS I NEED RPM's at 1500 during the test (dang it has been a long day) get back out there and follow instructions and post readings if you want some help. Heading out to local bar soon s you got like 30 minutes LOL.

ARFFAZ Enthusiast

ARFFAZ

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Ok ran the test at 1500 RPM

 

Outside temp - 110

Hi port - 285 PSI

Lo port - 35 PSI

Vent AC temp - 40 deg

 

My initial test may have been inaccurate, i hooked up the high side this last test and got a 0 reading. After dinking around I realized the cheap harbor freight coupler needle was not going down far enough to put the high port valve. I put a small ball bearing in there and it gave it the extra length to push the valve down.

Dnt Senior Enthusiast

Dnt

Posted
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Those are good numbers. The low pressure switch should not pull the electrical circuit until the low side drops below 25 or so. Put the guages back on and just make sure that the low side does not drop to below 25 when the truck is in park and idles. Pull and clean the compressor clutch wire connector and inspect the wiring as far back as you can follow it. Next lets inspect the wiring to the low pressure switch on the accumulator and the high pressure switch on the back of the ac compressor, clean and inspect the ends same as clutch connection. Now another known problem area is the fuse block connection pull the AC relay and carefully inspect the connections inside the block if you see anything suspicious there (black soot etc) that could make that suspect. I would like you to perform the clutch test when in park and the compressor kicks out does it immediately kick back on if you tap the front of the compressor clutch with a long handle screwdriver? I am suspecting that the clutch air gap is too wide to allow the electromagnet to hold the clutch pulled in! Can be reshimmed if that is the issue but requires some specialty tools...

txab Senior Enthusiast

txab

Posted
Posted

Those are good numbers. The low pressure switch should not pull the electrical circuit until the low side drops below 25 or so. Put the guages back on and just make sure that the low side does not drop to below 25 when the truck is in park and idles. Pull and clean the compressor clutch wire connector and inspect the wiring as far back as you can follow it. Next lets inspect the wiring to the low pressure switch on the accumulator and the high pressure switch on the back of the ac compressor, clean and inspect the ends same as clutch connection. Now another known problem area is the fuse block connection pull the AC relay and carefully inspect the connections inside the block if you see anything suspicious there (black soot etc) that could make that suspect. I would like you to perform the clutch test when in park and the compressor kicks out does it immediately kick back on if you tap the front of the compressor clutch with a long handle screwdriver? I am suspecting that the clutch air gap is too wide to allow the electromagnet to hold the clutch pulled in! Can be reshimmed if that is the issue but requires some specialty tools...

 

 

This^^

ARFFAZ Enthusiast

ARFFAZ

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Those are good numbers. The low pressure switch should not pull the electrical circuit until the low side drops below 25 or so. Put the guages back on and just make sure that the low side does not drop to below 25 when the truck is in park and idles. Pull and clean the compressor clutch wire connector and inspect the wiring as far back as you can follow it. Next lets inspect the wiring to the low pressure switch on the accumulator and the high pressure switch on the back of the ac compressor, clean and inspect the ends same as clutch connection. Now another known problem area is the fuse block connection pull the AC relay and carefully inspect the connections inside the block if you see anything suspicious there (black soot etc) that could make that suspect. I would like you to perform the clutch test when in park and the compressor kicks out does it immediately kick back on if you tap the front of the compressor clutch with a long handle screwdriver? I am suspecting that the clutch air gap is too wide to allow the electromagnet to hold the clutch pulled in! Can be reshimmed if that is the issue but requires some specialty tools...

Thank you for the reply, I have been waiting for the weekend to look at this. It is currently running 120-127 deg where I live and trying to work on an engine that already roasting after getting home from work in the heat is no fun.

 

I will go back through all the step you provided again tomorrow. Last I checked my relay was good, I even swapped it for another know working relay. The pin ports looked clean too. I have not yet checked the wiring at the connection to the clutch or traced it back. Could be a reason why the clutch will like to engage when it is sprayed down with water.

 

I already did the clutch test and had no luck. The clutch will not engage no matter where I hit it. The clutch seems to engage every 30-40 seconds for a 1-3 second period like clock work....like the computer is attempting to turn it on and it is not staying engaged. Once I wet down the clutch it engages and stays engaged.

 

I am leaning towards needing a new clutch assembly, I found one on autozone for 145. If I do narrow it down to this would this be a easy item to replace while the compressor is attached? If I had to remove the compressor might as well get a whole new unit. It looks straight forward though...Remove the belt, remove the center bolt, pull the clutch plate and shims, pull the pulley and then pull the coil. I know this to be true on other compressors but I am not familiar with the silverados. I am thinking I can get the puller tools from autozone on loan and knock it out in a hour or 2.

ARFFAZ Enthusiast

ARFFAZ

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Ok so I did some check this morning and this is what I got.

 

Turned on A/c and compressor did not try to engage at all.

Jumped low pressure switch and got no response.

Shut down truck and inspected connect for A/C clutch coil...looks good.

Ran direct 12V to connector and got clutch to engage.

Connected connect back together and started truck and A/C... did not engage.

Remove A/C relay and jumped pin 87 to 30 and got clutch to engage.

Connected gauges and got 10 on lo side and 100 on high side... outside temp was 110. now cold air at vents.

I am guessing I am low on refrigerant and the A/C pressure switch was keeping the system from kicking in....??? don;t understand why when I would spray off the compressor the compressor would engage and show good numbers... I would think cooling off the compressor would lower the pressures.

 

At a loss... Guess it is low... maybe clogged expansion valve...

muddkatt Senior Enthusiast

muddkatt

Posted
Posted

 

Connected gauges and got 10 on lo side and 100 on high side... outside temp was 110. now cold air at vents.

 

Those pressures show the system is nearly empty of freon.

ARFFAZ Enthusiast

ARFFAZ

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Yes I think I may have been leaking from the schrader valve. I will post more info after I charge the system.

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