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Formely SSierra08
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Discussion Starter #1
First what ive done.
New compressor
New accumulater
New orifice tube
New expansion valve
Blew out all the lines
Had it filled to around 50 psi at 1800
Checked the blend doors

With front and rear ac on full blast the compressor and the lines are sweating. The line from the accumulator to the firewall is cool but not cold.

I thought blend door but the rear or front would work if one is bad.


Im at a stand still!<br/>
 

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Do the lines at the rear get cold? And on the accumulator there should of been a weight of the capacity of the system.
 

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Formely SSierra08
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Discussion Starter #3
Yes low side does high side is hot. The accumulator didn't have that. Low side reads 55
 

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well that's a no then :)

for any air conditioning system whether it's in your car, you home central air or a window unit, or the freezers at the supermarket, the ac system can only have refrigerant in it. 100% refigerant, no air and no water/moisture.

when you had your ac system apart, it filled up with air at atmospheric pressure along with water vapor that's normally present in the atmosphere. you need to remove that from the AC system prior to charging it with refrigerant... which is known as evacuating the ac system with a vacuum pump. when you do that you pull nearly all the air out but most importantly the reduction in pressure allows water vapor to boil out and be removed. This is very important, because any H2O molecules in there when the AC system is running and refrigerant is under pressure will cause that H20 to freeze and cause a blockage. Also any water or oxygen in a running AC system will break down and oxidize the oil in there turning it to sludge, causing blockages and wrecking the compressor. Oh, and the ac system won't work right either, you'll never get cold air out your vents. The air that's left in the AC system (78% nitrogen 21% oxygen) is what's called non condensible gas, meaning it doesn't serve a purpose it displaces refrigerant and it prevents the ac system from working. it's like putting water in your fuel tank- your engine won't run because water doesn't combust.
 

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Formely SSierra08
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Discussion Starter #7
I did pull vacuum on it. I dont know the right amount of time but I prob did 30 min. Do I need to flush or "wash" the lines? I did reverse flush the lines.
 

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what/how did you pull vacuum? how much vacuum did you pull, what type of gauge did you use?

the most common causes of poor ac performance are not pulling deep enough vacuum on the system to remove air and moisture, too much air is left in the system displacing refrigerant. the other is an incorrect charge of refrigerant, generally not enough.

you didn't mention why you did what you did. if you had compressor failure previously or other major problem what is common is for the condenser to get plugged up. and it's been reported that certain types of condensers (parallel flow vs series or whatever) have tiny passages that get clogged where flushing is not effective. so the recommendation is to put in a new condenser if ever not sure.
the other big thing is flush solvents used, most are not approved by the car maker (GM/Ford etc) and they can leave residue and cause problems.

the outlet high pressure line from compressor should be hot as it goes into the condenser. The line from condenser to the orifice tube should be warm. the line after the orifice tube going thru firewall to the evaporator should be cold but not necessarily ice cold or really cold. you should feel a definite temperature change before and after orifice tube. the line coming out of firewall from evap to accumulator should be cold and sweating along with accumulator if it isn't wrapped. the suction line from accum. to compressor should be cool but not as cold as accumulator.
if you feel temp change in a line anywhere other than orifice tube location, you have a blockage.
 

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Formely SSierra08
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Discussion Starter #9
He used a vacuum that hooked up to the low side port. He does commercial ac for a living so right tools but we are not car ac pros. I have read that I need 1-2 hrs of vacuum. I did because only the front ac was working (blowing cold) so I changed the rear exp valve as it was clogged with oil I assume. The tahoe didnt have air when I got it but clearly had new compressor. I put freon in and it worked fine till I drained it to install the valve. The last paragraph ill have to check tommorow. I really appreciate the feedback!
 

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i'm not familiar with the trucks having 2 or more zones for climate control,
I ASSUME that there's only one evaporator coil in the dash that cools the air for the entire vehicle and then the cold air is vented to the rear. if so, it's basic AC service so it should be straight forward to fix. But you said you changed rear expansion valve so that leads me to believe you have one compressor pumping liquid refrigerant and that liquid line splits however to 2 or more zones each having their own expansion valve (orifice tube ? ) and their own evaporator coil. in this case troubleshooting is a little more involved. that rear expansion valve should not clog, certainly not with clean PAG oil. if it's clogged, you need to determine what/why it clogged, I'm guessing debris in the system from failed compressor. it's very important to flush everything and remove all contaminants, otherwise it'll lead to problems.

the duration of vacuum is eh, you need to pull below ~2000 microns ideally below 1000.
once you get below 1000 microns you don't 'need' to keep pulling for hours, 10-20 minutes is ok then let it sit with pump off and see if vacuum holds. if it holds less than ~4000 microns for ~30 minutes you're good, how long you decide is subjective. it's a small system having less than 2 lbs vs a large system so your friend certainly doesn't need to follow guidlines he might be used to for large systems having 10+ lbs of refrig.
 

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Formely SSierra08
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Discussion Starter #11
There is a seperate evap in the rear. Its a evap with expansion valve and a blows motor. The air is pumped up thru a tune to the rear seats. We blew co2 thru all the lines prior to install. The old valve I took out was clogged with burnt oil. I made have made a big mistake but I havnt added pag oil!
And the accumulator isn't sweating.the other lines and compressor are
 

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Formely SSierra08
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Discussion Starter #12

Ron I think I found it. The line running to that junction block is cold, the line running down to the rear is cold but where im pointing after the block, accumulator and the line running to the firewall are warm. So my block would be in that block prob....right?
 

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i'm not sure. you (and I) have to understand the direction of flow in the system... what lines are what and going where, put little paper labels with arrows on them if need be if it's all crazy there.
the compressor pumps thru the outlet - then to to condenser - then to a junction where that high pressure liquid line splits because you said you have 2 evaps so one line goes to front evap and one to rear evap. the lines coming back from each evap will then T into each other, then one line runs to accumulator then the suction line from accumulator to compressor inlet. you need to verify that, i'm saying this as an educated guess based on what you've said so far.

how refrigerant is regulated thru evap i don't know for sure, are they using a thermostatic expansion valve at each evaporator or is it orifice tube? you've been saying orifice tube, if that's what used on yours 2 orifice tubes i don't know if there'd be any check valves or balancing valves somewhere.... i'm not familiar with your split system on the tahoe is certainly something you'd want to look up in a GM service manual to know for sure how it all works. with extra mechanical shit like that in the system naturally is just another thing cause problems or need replacing, and they can be hard to recognize.

when i said temperature change, it's from hot to cold because it's when high pressure refrigerant that's a liquid drops to a lower pressure, boils and expands into a gas. just like the orifice tube which is a simple restriction of a certain sized hole- a blockage in a line will do the same thing and the pressure drop after the restriction will [usually] cause a temperature change from warmer to colder. it's a troubleshooting method.

so in your pic i can't really tell but the junction looks like it's on the return where that line going up and over then the rubber down to the right is the suction line to compressor. i can't tell how the accumulator is hooked up in your pic. on the return line from accumulator to compressor, it will get warmer as it picks up heat along the way but it shouldn't be a drastic change at a pinpoint location, if it is then likely there's a blockage. hope that helped.
 

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google, or check underhood or owners manual for that.

for front/rear ac system looks like 11 oz PAG-150 oil total. so you account for whatever oil is already in system then add to achieve a total of 11 oz.

for refrigerant charge i'm seeing anywhere from 46 to 64 ounces.
 

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http://www.autoacforum.com/messageview.cfm?catid=20&threadid=9172

if you didn't do it complete already prior to installing new compressor, you need to unbolt and remove basically everything except the evaporators (unless you're crazy and like to work on your truck). the compressor and accumulator you don't flush, just dump all oil out of them. if any debris comes out of accumulator, get a new one. if you're accumulator is new but only has the 1/2 hr run time on it you can probably reuse it, but if you pull your orifice tubes out and find they have debris in them then get a new accumulator. and if any of that happens and you didn't already replace it, it would be a good idea to replace the condenser as those don't flush successfully.

that's if you want to spend the money on the tools to do it yourself, which is only worth it if you prefer to do the work yourself and already have a good vacuum pump or access to one. otherwise it's worth it to bring it to a licensed ac shop who will stand behind their work.

http://www.angelfire.com/biz7/johnsresume/Condensers.htm

i'm looking up your stuff on rock for '99 tahoe with rear air,
http://www.rockauto.com/catalog/moreinfo.php?pk=818703&cc=1353721
if you have hose assemblies like this you need to understand what the large chambers are in the hard line, you may need new hose assemblies if your previous compressor died and put debris in the system, otherwise you're taking a chance on wasting time and money trying to flush them. the relatively straight lines with nothing to them you can flush, but also consider age of the vehicle because lines that go from hard line to crimp to flex rubber hose are prone to leaking with age. so you have to sum it all up and price out all new lines vs flushing.

again i don't know the split systems on the gm vehicles having rear air but this was what i was afraid of, shit like this can cause you major headache, research it and verify it's flush-able otherwise buy a new one... consider hitting up other tahoe/gm forums that talk about rear ac with someone knowledgeable about a lineset like this. those chambers might trap debris you can't flush out and you need a new one.
 

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Formely SSierra08
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Discussion Starter #18
Mine seem blocked right there at the junction block. That other info was great thanks. What can I clean them with
 
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