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Discussion Starter #1
I just acquired a 1999 K2500 suburban. It has a 6.5L diesel and the 4L80E trans.

The issue it is having is no cold air through the vents. The blowers work and are moving air.

So far I connected my gauges and topped it off. It was a whole 12oz low. It might still need a little more but for now it has great high and lo pressures. The truck has cold water dripping from the front and rear evaporator coils. The rear vents felt cool, at night, but not nearly where it should be. The confusing part is how much water was dripping from the rear coil, it seems like it is getting plenty of air flow over the coil.

Also the side window defrost vent is blowing with the AC on.

So far I am thinking it is the blower door motors. At least for the front AC.

What do you guys think? Does anybody have a diagram for the routing of the AC lines? Does this system have 1 orifice tube or 2? Is it normal for the dryer on the firewall to not feel cold with the AC on. On all my pickups, the AC line that comes from the cab to the compressor is always cold. It is my understanding that the compressor is supposed to be refrigerant cooled. What is normal for these multi zone systems?
 

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Rear has one of the variable expansion valve dodads located at the rear. Front has a regular GM style orifice tube that could be right at the inlet of the evaporator at the firewall or on a 99 I think it would be just after the split in the high line, look for the dimples in the line just after a fitting. The dimples are the stopper to keep it from sliding in too far. Every truck with a rear system I have ever messed with had a plugged up orifice tube for the front making the front not cool. I'm not sure if that then causes the rear valve to adjust funny sometimes the rear cools oK other times not.

The 95-00 trucks are kinda known for having mode door issues. Mode doors are a set of 3 doors operated by one motor and some linkages just above the gas pedal. If you are super lucky you have a bad motor or a linkage that fell off just because but more likely something has fallen down the vents or just age has damaged the tar like seal around the edge of the top door which allows it to fall off its pivots and down into the other doors. Sometime in the last week or two someone else asked about the doors and I found the link to my old thread showing how I fixed mine.
 

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Wash the radiator stack.
You need to wash the evaporator which is accessible through the blower fan.
 

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Discussion Starter #4
I did some further testing. The mode door is working and the linkages are connected. It runs the full range of motion and all the vents cycle on and off. The temp door seems to be the issue. I can barely see it but I was able to see it go to heat. It only moves about 1/8 or 1/16 of a turn. How much should the temp door motor be turning? Are the linkages internal? How do you get that one out, it is packed in pretty good.

Cooling stack and evaps will get cleaned. I might evacuate the system and replace the orifice tube to be safe. But for now I just want to get cool air out of the dash. I know the evap coils are getting cold because both are dripping within minutes of running.
 

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Discussion Starter #5
Another update:

The cooling stack is clean as a whistle. The truck only has 46000 miles. I took apart the dash enough to see the temp servo and the marks on it. It was making its full range of motion. I hooked up the gauges again and looked up a pressure-temp-humidity chart. I was being cautions last night because I did not want to over charge it. For my conditions I need the low around 50 and the high around 220 psi. I was around 40 on the low. I added another 12oz can. The rear started to blow cold and after the whole can was in the dash vents started to blow cold. I think it was just low and the capacity of the system surprised me.
 

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Suburban takes a lot of refrigerant.
Not sure if it is still the same as 95 but there is a switch at the dryer, that is a weak point in this AC system.
IIRC, that is a low pressure switch and it can be replaced without leaking any refrigerant.
 

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Discussion Starter #7
Update:

The AC compressor is leaking and needs to be replaced. At least nothing failed and it is only the compressor. The rest of the components look brand new. How much r134a does the system take from empty?
 

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Original receiver had the label on it. I wrote it down on my new one so I will try and remember to go look tomorrow. It was quite a bit, I want to say something like 4 points and some odd ounces.
 

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IIRC, there is a better brand compressor for that year as supposed to ACDelco.
I am not sure if Sanden have a similar.
You may want to check the other forum where Thefermenator has a lot of knowledge about this.
He does not come here anymore.
 

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Its the mounts vs the stacked design of the compressor that causes this issue. About all you can do is set the thing on the mounts and rock it around a bit to see if it feels like its sitting square and flat. If its not you can try some shim washers but thats a sign that its going to be putting stress on the case which means eventually its gonna leak.
 

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Just remembered to check mine and I wrote 4 lb 4 oz which was what was printed on the sticker of what I presume was the original receiver dryer of my 98 Burb 6.5 w/rear ac.
 
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Discussion Starter #12
Just remembered to check mine and I wrote 4 lb 4 oz which was what was printed on the sticker of what I presume was the original receiver dryer of my 98 Burb 6.5 w/rear ac.
Thank you. I think I am going to go with the delco compressor. It is 192 on rock auto. I had to do the ac on my 96 a few years ago for the same reason. It is holding up fine. If the other compressor has better performance, I will consider it.
 

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Discussion Starter #13
Just remembered to check mine and I wrote 4 lb 4 oz which was what was printed on the sticker of what I presume was the original receiver dryer of my 98 Burb 6.5 w/rear ac.
Would you happen to know the part numbers for the orifice tubes? I may as well do them and the dryer while I have the system open.
 

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Have you check RockAuto?
 

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Discussion Starter #15
Have you check RockAuto?
Yes. They don't list a delco part for the burb with rear ac. Lost of them for the trucks w/o rear ac. NAPA does have a house brand part for the burb with rear ac.
 

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15097129 or 52477004 or FOUR SEASONS 38887 or ACD 15-5612.
It's the yellow .062 GM O-tube.
No rear air Burb uses the black O-tube.
The O-tube is just past the "Y", before the evap. There is only one.
 
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Discussion Starter #17
15097129 or 52477004 or FOUR SEASONS 38887 or ACD 15-5612.
It's the yellow .062 GM O-tube.
No rear air Burb uses the black O-tube.
The O-tube is just past the "Y", before the evap. There is only one.
Thank you. I am not new to the 6.5 but this is my first suburban. This really helps.
 

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That all sounds reasonable. I may have had one on hand for my 98 from when I did my 96 several years earlier. Seems like I bought all 3 options (colors) that my local Napa had because I didn't know which to use and on the 96 I capped off the leaking rear so I needed a different one than the 98 that still in theory had a working rear.

My 96 it was in the inlet of the evaporator. That was where I looked for it on the 98 but found it near the Y. When I capped the rear on the 96 I put it in the outlet of the condenser like many of the pickups had. The 96 was apparently an oddball because the custom AC shop could not find a cap to match the threads on one of the rear outlets. They had been around since these trucks were new and said they never saw one with different threads before so i don't know what was up with that. They were so puzzled by that they actually crimpped off and welded the line for me while I waited for free.

I may find out next summer if the 98 has the same odd thread issue because so far I have not been able to find any leaks but a charge only lasts for a few days. Capping off the rear seems like the easiest next step to try and eliminate possible leaks.
 

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Discussion Starter #19
That all sounds reasonable. I may have had one on hand for my 98 from when I did my 96 several years earlier. Seems like I bought all 3 options (colors) that my local Napa had because I didn't know which to use and on the 96 I capped off the leaking rear so I needed a different one than the 98 that still in theory had a working rear.

My 96 it was in the inlet of the evaporator. That was where I looked for it on the 98 but found it near the Y. When I capped the rear on the 96 I put it in the outlet of the condenser like many of the pickups had. The 96 was apparently an oddball because the custom AC shop could not find a cap to match the threads on one of the rear outlets. They had been around since these trucks were new and said they never saw one with different threads before so i don't know what was up with that. They were so puzzled by that they actually crimpped off and welded the line for me while I waited for free.

I may find out next summer if the 98 has the same odd thread issue because so far I have not been able to find any leaks but a charge only lasts for a few days. Capping off the rear seems like the easiest next step to try and eliminate possible leaks.
I need the rear AC. This is a family hauler and the back seats need to be cooled. It was blowing cold and had the back feeling like a refrigerator when I charged the system. Hopefully the compressor is the only thing leaking.
 

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The rear lines have never been reproduced and have been out of production for a while now so can be very hard to find if you need them. Hopefully you won't. I think the all the under hood lines related to the 6.5 and rear AC are the same deal so be careful when working on them not to damage anything.

I think the reason the rear seems to work better than the front is it uses a valve like the 60's systems used that is variable and larger than the orifice tubes so it can adjust for a less than optimal system and possibly pass smaller chunks.
 
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