88-94 5.7 Suburban A/C Diagnosis and Tuning

[L31MaxExpress]

I just got back from taking a trip to Old Air Products. 109F and 20% relative humidity right now. Front ac got down to 40-42°F at highway speeds which was comfortable. Then I got into several miles of stop and go traffic under 10 mph. It warmed up to 50, then 55, the 60, and then 65, then settled out about 68°F. Definitely not right. I bought one of Old Air's expansion valves for their Hurricane unit. I am going to try a Made in the USA rear expansion valve. I picked up a capilary mounting clip that this unit has never had as well. Hopefully that will get the system operating correctly. While I have it apart, I am going to swap to the GM HT6 I have. I just do not feel the Sanden has the umph to pull dual evaporators correctly in this heat.

 

[cjcb1100]

107 here and 80 on the highway got 49 degrees best so far but barely able to keep me from sweating

 

[L31MaxExpress]

I am actually about to take a trip to the Oreilly hub store a mile from me. They show to have an 88947 in stock. Might as well put that on rather than a used HT6. If it works well, it is staying anyway. I just found a couple of sellers of the 88947 showing it is a 210cc displacement compressor. If that is correct, that makes it larger in displacement than an A6. That could make for some serious BTU improvements especially around idle. The 88947 is allegidly 210cc, the HT6 is 170cc and the Sanden SD7H15 is 155cc. If the 88947 has a standard DKS17D gut pack it is still 175cc. I have not found conclusive information from Four Seasons stating the displacement. They all show to have right at the same diameter pulley. 4.25-4.33". I need to return the wrong expansion valve that I bought first anyway.

 

[L31MaxExpress]

107 here and 80 on the highway got 49 degrees best so far but barely able to keep me from sweating

Yea I do not understand the problem you are seeing at all. With a mostly clogged rear expansion valve and the VOV mine was throwing ice cubes with the Sanden. As soon as I got the rear system flowing again, that is when I ran into issues. After I year I ran into what the VOV has for a reputation and why I have typically avoided them, it failed and was hanging closed, causing short cycling from limited flow.

I do notice a commonality between our issues. We all 3 have Sandens and are in basically the same climate. I feel that may in itself be a clue worth investigating. Hence the compressor swap I am about to do.

 

[L31MaxExpress]

That would make sense that the later 88947 compressor pumps more than the earlier Sanden. R-134 requires a larger compressor to achieve the same cooling capacity as R12.

I've been following your work because I really want to put good A/C in Roscoe, and I appreciate you sharing all the part numbers and descriptions. I think I need to order an 88947 instead of the GM GENUINE 1520185 "R134 retrofit" compressor. The only problem is going to be mounting it with a TBI serpentine belt setup.

I forget what year you have, but the 88947 fits the Vortec brackets. About to try one out myself.

 

[L31MaxExpress]

So I have the Old Air expansion valve, 88947 (I went ahead and bought the $50 AC kit to get a lifetime warranty on the compressor) and a Red Ford Orifice tube in my hands. I blew into both the Old Air and wrong chinese valve I returned (Allegidly an OE spec replacement R134a valve with a 2 ton capacity for a 1997 Express with OE rear air). The flow volume on the Old Air valve is easily half. Hopefully that is indicitve that the expansion valve change will fix my unit and I am sure added compressor capacity will not be a bad thing. I mean 10 cylinders instead of 6 should in theory have a bit more capacity. Now I am waiting on my recovery pump and the engine to cool down with a fan on it. First step, get the valve changed and then maybe the compressor will be cool enough to remove.

 

[L31MaxExpress]

Orifice tube has been swapped to the Ford Red 0.062". The 88947 is ready to go on now. Correct 430 psi cut-off switch installed. Still waiting on the engine to cool off a bit. About to tackle the rear expansion valve. Allegidly the 88947s are more resistant to leaking than the OE HT6, we will find out.

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[L31MaxExpress]

Well I just cracked open a cold refreshment to cool down while the vacuum pump works. It was nearly to 30 in/hg when I walked away. Expansion valve is changed, I will wait until I charge the system to put the rest of the rear unit together this time. That sticky tape is a real mess. Compressor was really the easy part, compared to the expansion valve. I sealed the Sanden up to keep it nice and clean. In an hour or so I will know how it works.

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[L31MaxExpress]

I am uploading a couple of short clips, but I have cold ac at idle again. Both units are around 50°F at idle and drop to ~38°F at ~2,250 rpm. Pressures are much better even with both blowers on high. It is 97°F and 38 RH at the moment and no sun load, but it is without a doubt cooling better at idle. This is the current pressures vs the 61.5/247 I had the other day at idle in the same weather also after sun down.

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[L31MaxExpress]

A few video clips I made.

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I was still adding refrigerant at this point and the accumulator had yet to get cold. The high side pressure dropped at full charge. Not unusual to see elevated high side pressures while you are charging a system especially before the compressor has cool gas making it back to cool the unit.

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After the interior cooled down, this dropped even more, to where it was holding about 45°F at idle.

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This was after about 2-3 minutes at a steady 2,000 rpm. The compressor actually cycled once during that time too.

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I am about to take it on a short test drive. Will also take it out during the heat of the day and report back.

I also cannot help but notice that your suburban calls for the same Four Seasons 38693 Expansion valve that started this whole process over for me again. The Old Air Expansion valve was a direct bolt in. I noticed with the 38693, I could switch the rear blower off and the suction lines were practically ice cold all the way back to the compressor. With the Old Air valve in place the lines are not nearly as cold because it is actually closing off flow as designed. So it was either a defective valve or built wrong. The Sanden may have done a better job had the expansion valve not been just blowing extra refrigerant through it, but more compressor capacity only helps these dual units work better.