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Old 02-14-2019, 08:44 PM   #1
LBJ
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2004 Silverado A/C - Bad Switch or Low Freon?

For 14.5 years the A/C has worked almost perfect on the 04 Silverado Ext Cab 5.3 Vortec. It was working fine a month ago, but the other day, I turned it on and ZERO cool air. The fan blows and the compressor clicks on, but no cool air. What is the easiest way to determine the problem? Is it the low pressure sensing switch or just low on freon? I have a set of freon gauges/lines I've had since my 1977 was my main ride, but not sure where to hook them up on this "new" truck. Thanks for any tips. LBJ
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Old 02-15-2019, 10:26 AM   #2
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

If the compressor is kicking on it's not the LPCO switch.

I assume you looked at the compressor to be sure the clutch is engaging the hub when it clicks. Not in an easy location to see from the top with that compressor buried down next to the frame and oil pan but you should be able to look up from underneath.

I'd hook up a set of manifold gauges and see what's what. Your 1977 R12 gauge set with threaded fitting hoses will not have the quick disconnect fittings for R134a.

You can use R12 manifold gauge hose to R134 service port adapters.
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Old 02-15-2019, 01:58 PM   #3
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

Thanks Hatzie, good information. I need to go get some R134a adapters for my old gauges.

Had a friend look at the clutch while I engaged it from inside the cab. He said it was engaging and wasn't making any noises. But, the little yellow light on the A/C power pushbutton would go off as soon as I pushed it, which it never does when working correctly. It finally came on and stayed on, but no cool air.

I'll look thru those service manuals to see where the 2004 hi and low pressure connections are.
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Old 02-15-2019, 02:02 PM   #4
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

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Thanks Hatzie, good information. I need to go get some R134a adapters for my old gauges.

Had a friend look at the clutch while I engaged it from inside the cab. He said it was engaging and wasn't making any noises. But, the little yellow light on the A/C power pushbutton would go off as soon as I pushed it, which it never does when working correctly. It finally came on and stayed on, but no cool air.

I'll look thru those service manuals to see where the 2004 hi and low pressure connections are.
I don't have any T800 service manuals scanned.

The R134a High and low service ports are easy to find and you can't mix them up.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old 02-15-2019, 02:10 PM   #5
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

I'm looking at YouTube for some visual instructions. Should get me going. Thanks, LBJ
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Old 02-15-2019, 06:37 PM   #6
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

I am going to throw this out there just in case .

One thing that is bad to give problems is the actuators that control the blend door . It will not control the door proper and will introduce heat from core and feel like the a/c is not working . Being the compressor is working this may be a realistic problem .
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Old 02-15-2019, 06:55 PM   #7
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

Hi homemade87, I just replaced one Heat/AC door actuator last year and that fixed that. So, hope it's not another one that's bad. Ha. Thanks, LBJ
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Old 02-17-2019, 11:32 AM   #8
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

I ran the A/C system the other day and felt the aluminum lines to see if it was getting cold. The air temp was about 55 Deg F so they were cool, but not COLD. I also checked the air vents to see if the air changed from cold to hot when changing the temp levers. They appeared to work as normal - full cold to full hot to full cold. So, the actuators all seem to be working fine. Since my A/C charging manifold is way out of date with current refrigerants, I'll borrow a set from a friend to check pressures, or buy a new set. No use messing with all the adapters. Still a few months before HOT temps around here, so, no hurry on getting it figured out. LBJ
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Old 02-17-2019, 12:12 PM   #9
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

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I ran the A/C system the other day and felt the aluminum lines to see if it was getting cold. The air temp was about 55 Deg F so they were cool, but not COLD. I also checked the air vents to see if the air changed from cold to hot when changing the temp levers. They appeared to work as normal - full cold to full hot to full cold. So, the actuators all seem to be working fine. Since my A/C charging manifold is way out of date with current refrigerants, I'll borrow a set from a friend to check pressures, or buy a new set. No use messing with all the adapters. Still a few months before HOT temps around here, so, no hurry on getting it figured out. LBJ
Good deal , sounds like you are getting a direction to go to getting it figured out . Let us know what you find .
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Old 02-17-2019, 01:58 PM   #10
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

If you figure it's low on refrigerant and the compressor is kicking on you need to be prepared to replace the LPCO switch.
I would also disable the compressor til you get it sorted so you don't burn it up.
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1969 Dodge Polara 500 B383, A833 SOLD
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1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old 02-17-2019, 02:46 PM   #11
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

OK, thanks guys, I'll keep you posted. By the way, I might as well just buy the R134a adapters for my manifold set as I have forgotten I had the 77 Chevy changed over to R134a 5 years ago! I'm getting old, it appears. Ha. LBJ
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Old 02-17-2019, 02:56 PM   #12
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

If your older gauges and valves are better quality than you can buy now just get a set of R134a Hi & Low hoses to fit the manifold.

You can get can taps that fit the R12 charge hose.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
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Old 02-22-2019, 05:42 PM   #13
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

Hi Hatzie, I pulled out my manifold gauge set from the late 70's. Manufacturer is Continental Precision Instruments in Ft Lauderdale FL. The only stamping on the manifold is "A49." They were top drawer as I recall and still appear to be in fine shape. My question is, are the gauges going to be OK for use with R134A with the proper adapter hoses?
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Old 02-22-2019, 05:58 PM   #14
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

Those look like decent gauges. If those gauges are working I would just change the hoses over.

Check your gauge manifold valves for leaks.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
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Old 02-22-2019, 06:05 PM   #15
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

Hatzie, without buying the new adapter hoses first, what is an easy method to test the rig for leaks?
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Old 02-22-2019, 06:25 PM   #16
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

You can fix leaking valves without much trouble. Usually they're just fine.

Get some brass fittings and hook the manifold to your shop air at 60 psi or so.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old 04-16-2019, 09:31 AM   #17
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

Update to the A/C story. Thru an unexpected "find" of a good A/C guy I lost track of several years ago, I was able to get him to look at the 2004 Chevy. He's a professional mechanic with the full 134a capture and replenishment freon machine. First, he tried to pull a vacuum and didn't get anything with that attempt. Next, he said he was going to put some 134a into the system to try to get a reading. That attempt failed also, Not sure what he did next, but he tried something different with adding the 134a. In the process, we both heard a "pop" in the line next to the drier and then the system took a full 1.6 pounds of 134a. He started the engine and tested the A/C. It worked! He said he could only guess there was something in the lines that popped loose. Might work well for a long time or blow out tomorrow. Hard to tell, but said I could run it and see what happens. For $50, that was a cheap fix. He said if the compressor was bad or goes out, the whole replacement would be about $850 which includes a new condenser and drier. That's $500 less than the Chevy dealer quoted on a worst case, compressor out, situation. While I was at it, I went back home, got the 77 Bonanza and had him refill the 134a in that one. Worked fine. Not bad for a 42 year old truck A/C system. That was $99. Took about an hour to completely vacuum the system and refill. I had him replace the Schrader valves while he was at it, just in case they were bad. So, back in business on both trucks. Thanks for all the suggestions and help, all you guys! LBJ
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Old 04-29-2019, 11:51 PM   #18
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

The low side service port (Schrader valve) is a very common leak area on these trucks. If your A/C starts blowing warm again spray some soapy water on the low side service port...if it bubbles it wouldn't be a bad idea to replace both high and low side fittings
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Old 04-30-2019, 11:46 PM   #19
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Re: 2004 Silverado A/C - Bad Switch or Low Freon?

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The low side service port (Schrader valve) is a very common leak area on these trucks. If your A/C starts blowing warm again spray some soapy water on the low side service port...if it bubbles it wouldn't be a bad idea to replace both high and low side fittings
I see the highside leaking more then the low sides on these trucks the high side uses a hars rubber ball to seal i found out the replacments leak worst then the old ones so i fou d there is a r12 to r134 vavle that screws right in place on the new trucks and uses a scader vavle i stead of the rubber ball to seal
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