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A/C Overhaul/Compressor Replacement How-To

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Old 07-10-2012, 11:21 PM   #1
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Exclamation A/C Overhaul/Compressor Replacement How-To

OK this is for second gen trucks, but the principle is the same for any vehicle.

NOTE/DISCLAIMER: I will NOT be doing a super detailed how-to on this a/c repair. this repair requires you to know what you are doing to prevent damage to the a/c system, so i wont be going into detail on how to remove the a/c from the engine...etc. if you cant figure that out, you probably shouldnt be working on a/c. basic mechanic skills needed to physically replace the parts. Proceed at your OWN RISK!! if you are new to a/c repair READ this thread A FEW TIMES BEFORE ATTEMPTING REPAIR!!! This how-to is based on a/c compressor failure/general leak and the process to fill the system.

OK now that is said and done here are some PDF files i acquired.

This is the general fill up and recommended pressures @ temps on page 10.
https://docs.google.com/open?id=0B0R...HJPZEc4d2JScmM

This one is more of the overhaul, BOTH contain/cover the same info, but its good to have both. it may say "preview not available" but you still have the option to download it. this PDF should cover any repair not listed in this how-to.
https://docs.google.com/open?id=0B0R...1NRQVF2ZjNUTlk

So, finally did the a/c on the ZR2 and decided to do a writeup about it, being summer is here and a/c questions are always being asked.

i purchased the A/C manifold gauges from Harbor Freight for $40-60. it does the job gauge wise as it's accurate, but yeah the knobs are fragile so don't crank down on them to close the valve. compressor... either buy new OEM, or a good new aftermarket, rebuilt compressors don't seem to last as long.

The system in the 2nd gen trucks hold 28oz of 134A, and 8oz of PAG oil. use the PDF above to see more information on the system specs.

ITEMS NEEDED
  • A/C manifold gauges
  • 28oz 134A
  • PAG 150 oil (or whatever your compressor comes pre-filled with, make sure you check that. use what the compressor comes with, flush out the old oil.)
  • a GOOD vacuum pump (CAN BE RENTED AT AUTOZONE WITH THEIR RENTAL PROGRAM. ITS FREE!!)
  • A/C compressor
  • Accumulator/dryer
  • O-ring kit
  • orifice tube
  • basic hand tools with some decent sized wrenches
So here are the materials gathered.


first, make sure the system is completely empty unless it has already leaked out. a shop with a recovery machine can remove your old 134A if the system still holds pressure.

second, remove the intake...2.2, or 4.3 you will need to do this. again, if you cant figure this part out, stop and seek a professional to complete the repair or READ the PDF above to learn more about the a/c system and removal procedure.


Remove the serpentine belt, then remove the compressor, 4 bolts attaching it. and the a/c lines and the clutch connector up front. on the 4.3 models the high pressure switch is located in the back of the compressor, so don't forget to unhook that before removing the compressor.


4.3 owners, Chances are your new compressor will NOT come with a high pressure switch....so flip your old compressor over and using a snap ring tool, remove the high pressure switch and install it on your new compressor. the new compressor will have a plug, as shown below. remove and install the switch here. clean any debris from the switch to make sure it seals. or buy a new switch if you suspect the old one to be bad.


where the old is leaking. generally these compressors leak in the middle. you could wash the compressor/oil off with water and see if oil appears, if so, you have a leak. discontinue further use of the compressor to prevent more damage to the system.

Thought i heard a loud hiss when turning the a/c on one day. apparently some 134A/oil blew out lol.


using a pair of channel locks i kept the hardline/accumulator steady. its VERY IMPORTANT YOU SUPPORT THE ALUMINUM LINES WHEN REMOVING THE FITTINGS. FAILURE TO DO SO WILL CAUSE THEM TO BEND AND TWIST!!


simply unscrew the low pressure switch from your old accumulator (if still in good working order) this repair can be done on a fully charged system as there is a schrader valve to keep the pressure in.


orifice tube removal. it is VERY important you change this. the screen easily clogs, and is critical for proper a/c operation (and its cheap). it is located on the bottom of the evaporator coil, by the frame. needle nose pliers are needed (or a special tool) to remove it. it should come out easily. again, support the lines when removing the nut on the line. replace O-ring.



some metal shavings, but not bad. I've seen worse lol. now, if your orifice tube is packed with metal shavings, i suggest you replace the condenser up front. most likely its clogged with metal shavings as well and if you don't replace it, the orifice tube will just get clogged again and introduce contaminates in the system. i believe they sell for $120....a lot cheaper than a new a/c compressor/charge and would be cheap insurance....or just ignore what i typed and go ahead and don't replace it....see what happens

if you have nitrogen available you can blow out the lines to free any possible debris.




i grouped the O-rings for easier matching. that single black o-ring was a stock one. make sure you get the correct one and replace every o-ring from any connection you remove. you could replace ALL the o-rings but if its not leaking you don't have to...but that is a chance you will have to take, as the old ones could start to leak. lubricate the o-rings with mineral base 525 refrigerant oil...but if you cant get any you can use mineral oil to lubricate the o-rings...also heard dielectric grease works too but i don't know if i would use that. don't use pag oil to lubricate the o-rings. it attracts moisture and can corrode the fittings (or from what i have heard) make sure you do not torque the crap out of the lines! doing so can cause the fitting to leak too. just make sure its fairly snug, but dont force it.

If your compressor is shipped with oil, and its 8 oz, leave it. if your compressor was NOT shipped with oil, add the correct amount of pag oil to the system. refer to the PDF above for this info. rotate the compressor 10-20 or so times once installed to cycle the oil throughout it.


next, draw a vacuum for 40 minutes. suppose to be 30, but whatever, doesn't hurt if you do it a little longer. make sure you open the high, and the low side on the gauges and the valves are open on the quick connect. the valves on the quick connect you tighten down to open, sorta opposite, but it pushes down the valve on the line.

Close both high/low valves and turn the vac off for 10 minutes for a quick leak check. there was none. so let it sit for 20 more minutes to confirm no leaks. i do know some leaks can not leak on a vacuum, but can when pressure is present. also there is a chance the A/C manifold gauge could leak, or the quick connect... something to keep in mind.


So, now its time to fill the system with 134A. a hot pan of water helps prevent the 134A can from freezing. DO NOT TURN THE CAN UPSIDE DOWN WHILE FILLING!!! This could damage the compressor.

  • start the truck
  • turn the a/c on max
  • fan speed 4 or max.
slowly open the low side valve, DO NOT OPEN THE HIGH SIDE AT ANY TIME!! this will cause the can to pressurize dangerously and could EXPLODE. you are dealing with 150-300 PSI from the compressor going into a can that is not designed to hold such pressure.

so, the system would be filling up with 134A, the compressor wont be running at this time, but once the pressure builds enough it will kick on for a few seconds and shut off, and keep cycling slowly. every time the compressor kicks on, it draws in 134A from the can (it will get cold) you will also see the pressure increase on the high side, and the low side pressure dropping while the compressor is on.

after the first can the compressor should be running constantly, for the most part. the late model 4.3s and 2.2 have a variable displacement compressor, so they do not cycle on/off during operation.

after the second can the system should be blowing cold, open the 3rd can and use a digital scale to weigh it, add 2 more oz of 134A to fill the system. Refer to the pressure tables in the PDF for the correct high/low pressures. take note of the current ambient temperature, and humidity and follow the chart. page 10 of the first PDF will have it, as well as the second pdf. with ~28oz of 134A in the system, and at 1500 RPM with the A/C on max, and the blower speed maxed, the pressure should be very close to what the PDF files state.


Rev the engine to 1500 RPM as per GM manual. had to get creative LOL. you can fill the system at idle, but to get the final reading you need to do this step.
df87129c by bean4dip, on Flickr

it works! (forever alone )


close the valve on the high/low port quick connects, and remove. leak checking the high side port with some water. Sometimes, these leak, so it wouldn't hurt to replace the valve. on the high side port it simply screws off, it looks like one piece on the hardline, but in fact 2 pieces. make sure you use a wrench to hold/support the line before removing the port. the low side port likes to leak sometimes. even with a new accumulator/dryer. i use a pair of needle nose pliers to gently pull the schrader valve out. this should stop any leak at the valve. it also wouldn't hurt to run the a/c while checking the high port. as the greater pressures would likely cause a leak if one is present. using compressed air, remove the water from the port and let it dry before installing the cap.


results....


nice and healthy system sweats.


So hope that will help you guys getting A/C to work. please, do some reading before attempting this job. its easy once you get things figured out and understand. by no means am i a "pro" at a/c systems. but i do have enough knowledge to work on them. please, if anyone has any questions or suggestions, post your thoughts.

Last edited by beandip; 04-15-2014 at 08:58 PM.
Old 07-11-2012, 03:04 PM   #2
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Re: A/C Overhaul/Compressor Replacement How-To

Good job!
Old 07-12-2012, 03:32 PM   #3
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Re: A/C Overhaul/Compressor Replacement How-To

Very nice. I just replaced my high side valve and needed to pull a vacuum. Could not find any pumps for rent and didnt want to drop the coin on a pump.

So I ripped the pump out of an old refrigerator, attached an AC low side fitting to the "suck" tube on the fridge pump. Hooked up a cheap vacuum gauge to the pump and it was pulling -29. Hooked it up to the system and heard it belching air out of the oil for quite a while. Left it on there sucking for 45 minutes and then charged it back up with 2 1/2 cans (50 psi at 85*f). AC is now colder than a witches tit.

Totally a "hick" way of doing it, but it really didnt cost me anything besides the cans and high side valve.. Its a good solution for those who need a vacuum pump on a budget.
Old 07-12-2012, 11:05 PM   #4
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Re: A/C Overhaul/Compressor Replacement How-To

Just added that i rented the vacuum pump at autozone through their rental program. its free, just gotta pay the cost of the pump, and you get your money back when you return it.

forgot to mention this in my first post.
Old 07-13-2012, 02:42 PM   #5
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Re: A/C Overhaul/Compressor Replacement How-To

I already fixed my a/c but i was going to check out the links you posted. Do have them in something other then google docs?
Old 07-14-2012, 01:09 AM   #6
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Re: A/C Overhaul/Compressor Replacement How-To

i can email, i think....not sure what the size requirements are for google, but the second link i posted is 40 mb or so.

but you cant get google docs to work? trouble viewing?
Old 07-14-2012, 02:52 AM   #7
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Re: A/C Overhaul/Compressor Replacement How-To

I dont have google docs. I think you have to sign up for it so i cant see anything when i click the links, just the home page for google drive. If you have to sign up to see it then it might be good to have a different way to access the information, if possible.

Nice write up BTW
Old 07-14-2012, 04:10 AM   #8
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Re: A/C Overhaul/Compressor Replacement How-To

I didn't have to sign up to view Phil's google docs.
Old 07-14-2012, 09:20 AM   #9
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Re: A/C Overhaul/Compressor Replacement How-To

I think the rental pumps are ymmv depending on the location. I went to advanced, oreillys, and autozone all of them gave me a clueless look and said no when I asked about one. This is the armpit of the united states though so Im not surprised.
Old 07-14-2012, 02:15 PM   #10
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Re: A/C Overhaul/Compressor Replacement How-To

Thought firefox might be blocking it but wont work on explorer either. Not sure oh well
Old 07-14-2012, 10:58 PM   #11
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Re: A/C Overhaul/Compressor Replacement How-To

odd.....you should be able to view them. if anything be logged into gmail. let me see if i can correct this.

:edit: ok, apparently when i uploaded them they were set for private. i set them to where anyone with a link can view, no sign in required. let me know if it works or not.
Old 07-15-2012, 01:59 AM   #12
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Re: A/C Overhaul/Compressor Replacement How-To

Thanks for posting this, I have put off buying stuff to do A/C work myself cause I didn't know the pump was available as a rent-a-tool.
Old 07-15-2012, 01:43 PM   #13
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Re: A/C Overhaul/Compressor Replacement How-To

Its still asking me to sign into google docs. I'm not signed up w/ google docs but i was signed into gmail and it still didnt work. Ive never used google docs so maybe its just me
Old 07-18-2012, 11:18 PM   #14
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Re: A/C Overhaul/Compressor Replacement How-To

Beandip .. (just my 2 1/4 cents.., nothing personal meant by it...)

Where's the flushing of the system ??? I, personally ,would NEVER install a new system without flushing out the lines, condensor, and evaporator extremely good. Especially if the orfice tube came out looking like that above !!! I am willing to bet that that condensor weighs a bunch ....

It Just my thoughts on the subject..., Flushing the system.., it's extremely cheap insurance when the price of compressors run from 100.00 up to 400.00 these days....

Advance and Orielys sell pressurized flush in a can for around 16.00 (tall can with a hose attached to it with a rubber tip on the hose..)
Poor mans way..., carb cleaner.., or brake clean and then use pressurized air... Anything, really, that will cut thru grease and that can be blown out of the line with pressurized air....

I just did two of these today... one in a blazer and the other in a dime.... 37-41 degree temps....

And Awesome tutorial above...,Just thought I would ask about the flush part...

l8taz,
Allen
Old 07-19-2012, 12:57 AM   #15
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Re: A/C Overhaul/Compressor Replacement How-To

Nothing personal taken, its a valid question.

i did blow out the lines with nitrogen, all that came out was some clean pag oil. nothing black or chunky . nothing looked like how the orifice tube above (pic made it look worse than it actually was)

generally if a system experiences complete compressor failure, as in the whole thing seizes up, then yeah, flushing wont save the condenser and replacing it is your best bet...

in my case, i had a few "large" metal shavings caught in the orifice tube, nothing serious. the a/c blew perfectly cold too. its a good thing sorta that the orifice tube clogs up easily. basically a filter I did catch the oil leak soon though. i'm sure if i didnt i would have to replace condenser as well. (it was stock sealed a/c system)

those flush cans, i figured they were crap honestly. i never used one but i suppose they do work. i just didnt feel like introducing more possible contaminates into the system by using a "flush" kit, and having the leftovers of that kit sitting in the bottom of the condenser.
Old 07-19-2012, 07:45 AM   #16
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Re: A/C Overhaul/Compressor Replacement How-To

I don't want to add much since I don't know alot, but on the options of a poor man's flushing liquid, add rubbing alcohol. I hold the hoses up high and pour it in both directions and then blow it out. I like rubbing alcohol cause its not as harmful as carb or brake cleaner and evaporates almost as well.
Old 07-20-2012, 07:41 PM   #17
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Re: A/C Overhaul/Compressor Replacement How-To

here is the orifice tube we pulled out of an 01 tahoe with rear air (that was fun). complete compressor failure....needless to say we had to replace just about everything. the screen on the orifice tube was crushed (imploded) and filled with metal shavings.


Last edited by beandip; 04-15-2014 at 09:00 PM.
Old 08-09-2012, 05:02 PM   #18
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Re: A/C Overhaul/Compressor Replacement How-To

nice writeup! my 02 blazers AC died the other day, thought i would try just refilling it and seems to last a day or so then it leaks out. do the storebought UV dye kits work at all?

i replaced the low side shrader valve already as i checked it about 2 months before it died as it didnt feel as cold of air and thought it could have not seated well.

whats the common failures with this AC system?
Old 08-10-2012, 06:26 PM   #19
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Re: A/C Overhaul/Compressor Replacement How-To

compressor
Old 08-13-2012, 06:26 PM   #20
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Re: A/C Overhaul/Compressor Replacement How-To

well...just about a month after i charged the system...guess what? it cycled on me the other day....threw the gauges on it, low charge. i soaped all the connections i took off and others, found out the high side port had a tiny leak, so i poked at the rubber valve and it stopped, then i noticed that there was some liquid refrigerent/oil on the low side port.

turns out the schrader valve was loose a little more than 1/4 turn and leaking from there

so time will tell now.....
Old 08-13-2012, 09:01 PM   #21
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Re: A/C Overhaul/Compressor Replacement How-To

do those do it yourself UV detector kits work at all?
Old 08-14-2012, 12:28 PM   #22
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Re: A/C Overhaul/Compressor Replacement How-To

from what i have seen, they do work. the stuff is uv reactive and dyes the oil, so if it leaks, you should be able to see it. really not much to it.
Old 08-15-2012, 12:13 AM   #23
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Re: A/C Overhaul/Compressor Replacement How-To

cool. ill have to do that i guess. im guessing its cheaper to do it yourself than pay someone? those friggin 134 cans are like $12 a pop haha
Old 08-15-2012, 01:55 AM   #24
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Re: A/C Overhaul/Compressor Replacement How-To

in solidarity to you on the forever alone man.. feck.

was actually reading this awesome fucking manual you produced and thinking.. I need someone around here.. as it is i am going to pay a guy who works with my const. co. to help me swap out my trans'.. lol jeeze.
Old 08-02-2013, 01:08 PM   #25
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Re: A/C Overhaul/Compressor Replacement How-To

Great write up, what is the correct compressor part number we should buy for a 4.3L 2000 Sonoma? I prefer AC Delco.
Old 08-02-2013, 05:19 PM   #26
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Re: A/C Overhaul/Compressor Replacement How-To

Quote: Originally Posted by dmarti
Great write up, what is the correct compressor part number we should buy for a 4.3L 2000 Sonoma? I prefer AC Delco.
I prefer the Sanden A/C compressor over the AC Delco belly leaker.

http://www.sanden.com/productsearch.php?model=4261
Old 06-14-2014, 05:33 PM   #27
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Re: A/C Overhaul/Compressor Replacement How-To

Thanks so much for this write up. Just got done replacing everything mentioned and had it charged. Blowing cold air compared to the warm before this quick fix. Bring on the heat.
Old 06-28-2014, 03:01 PM   #28
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Re: A/C Overhaul/Compressor Replacement How-To

Before I spend the money, any other ideas on my system on my 85. There was nothing in it, so we put 134 in and it blew cold for a week. Then nothing, the back of the compressor looked liked it leaked there. We vacuumed the system and my uncle said it held for like 30 minutes. I tried putting more in, just to double check, but it won't even take anything, the gauge on the can doesn't move when pull the trigger, the compressor is running. I don't know long the system hadn't worked, so could it just be clogged, the filter, or condenser?
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