88-94 5.7 Suburban A/C Diagnosis and Tuning

[L31MaxExpress]

Agreed on the last sentence. More on this in a minute...



Lots of great ideas, above, I have nothing to add (sadly).



On the Suburban / Tahoe, at least, there's a short (10") section of hose in the rear b/t the hard lines and the evaporator/TXV on the HP and LP segments. One could pinch off either the HP or LP lines, there, to isolate the rear system.



I wondered the same thing, but @Wildblue19 your Sanden has the same displacement as mine and @L31MaxExpress' Sandens. Too, your pulley is a little bigger than ours IIRC but it's in the ballpark. You should be OK in that regard if the compressor is functioning properly.

You haven't mentioned any unusual compressor noises, so I assume it hasn't lost its integrity.

I would only pinch the high side line, pinching the suction line is a bad idea. The evaporator core is not designed to withstand high side system pressure since the orifice is upstream of it.

His belt ratio far exceeds mine. I have a 6" diameter crankshaft pulley. I do idle at 850 in Park with the ac on and 750 in drive though with my cammed 383 and loose converter. At 1,250 engine rpm, my high side pressure is ~290-300 psi and the low side is about 32 psi. IIRC we decided the 4261 has a 4.11" pulley. Puts my compressor at ~1,850 rpm. At 1,500 rpm my compressor is spinning 2,200 rpm, the high side is still about the same, fan really moving air at that point and the low side drops into the upper 20s. The vents are blowing low 30s at that point and the compressor starts to cycle. So in short I do not see it being a compressor capacity or belt ratio issue.

You must be registered for see images attach

 

[1998_K1500_Sub]

I would only pinch the high side line, pinching the suction line is a bad idea. The evaporator core is not designed to withstand high side system pressure since the orifice is upstream of it.

Duh. Why didn't I think of that.

His belt ratio far exceeds mine. I have a 6" diameter crankshaft pulley. I do idle at 850 in Park with the ac on and 750 in drive though with my cammed 383 and loose converter.

I have an OE 8" crank pulley, I assume @Wildblue19 does as well.

Both @L31MaxExpress and I use the Sanden #4261 which has the smaller (~112mm) pulley. I believe Sanden specs the #4261 for the Express vans. As for GMT400s, Sanden specs the #4440, which has the larger OE-sized (~132mm) pulley. I elected to use the #4261 b/c of its smaller pulley, i.e., to garner the higher pumping for a given engine RPM.

@Wildblue19's Sanden 4864 has a 119mm pulley. So his ratio is in his favor.

All our compressors are 9.5 cu in displacement.

 

[L31MaxExpress]

Duh. Why didn't I think of that.



I have an OE 8" crank pulley, I assume @Wildblue19 does as well.

Both @L31MaxExpress and I use the Sanden #4261 which has the smaller (~112mm) pulley. I believe Sanden specs the #4261 for the Express vans. As for GMT400s, Sanden specs the #4440, which has the larger OE-sized (~132mm) pulley. I elected to use the #4261 b/c of its smaller pulley, i.e., to garner the higher pumping for a given engine RPM.

@Wildblue19's Sanden 4864 has a 119mm pulley. So his ratio is in his favor.

All our compressors are 9.5 cu in displacement.

I added to my belt ratio post above. I had previously taken some measurements when I did the oil return test.

 

[Wildblue19]

Back with more.

Clutch when hot is certainly not locked up, but feels like stirring honey, and the air flow is enough to get a microfiber towel to stick to the front of the grille.

Before pinching the rear high side, the temps at the rear high side line were 110°F and cold side 88°F. After pinching the high side, I verified both were the same within a few degrees.

Front vent temps with the rear isolated are 2 degrees cooler.

Running a stock OE pulley.

R-134 source is a 30# bottle from eBay, made in India. Could be contaminated. Where do you source 152?

Compressor sounds good, positive clutch lockup and not abnormally hot.

 

[L31MaxExpress]

The more I look at his numbers the more I start to question contaminated refrigerant. Might be worth stopping by a local shop with a refrigerant identifier just to know.

 

[1998_K1500_Sub]

OK, so...

- We think the compressor's working as it should
- We think the compressor has suitable pumping capacity, as-driven
- We question whether the gas mixture is contaminated
- The subcooling seems acceptable at 130F, but the system's not operating correctly so this number may be skewed

What did I forget?

- Superheat from the front evap was high, but might have been due to other factors (low charge; rear TXV hogging)

 

[L31MaxExpress]

Back with more.

Clutch when hot is certainly not locked up, but feels like stirring honey, and the air flow is enough to get a microfiber towel to stick to the front of the grille.

Before pinching the rear high side, the temps at the rear high side line were 110°F and cold side 88°F. After pinching the high side, I verified both were the same within a few degrees.

Front vent temps with the rear isolated are 2 degrees cooler.

Running a stock OE pulley.

R-134 source is a 30# bottle from eBay, made in India. Could be contaminated. Where do you source 152?

Compressor sounds good, positive clutch lockup and not abnormally hot.

That explains it right there. That india "R134a" is probably conterfit straight propane. Propane runs almost R22 pressures. Bleed a small amount into a cup and carefully try to light it. If it lights off that pretty much confirms it.

In my hydrocarbon experiments I have made the Propane R290 needs to be added in a 50/50 mixture with R600a aka butane to reduce the pressure. But that is for a different story.

I get my R152a from Sams club. 4 pack of 10oz cans is like $17.

 

[1998_K1500_Sub]

Before pinching the rear high side, the temps at the rear high side line were 110°F and cold side 88°F. After pinching the high side, I verified both were the same within a few degrees.

88F on the suction side? Why 88F, was the rear fan blowing on high?

Front vent temps with the rear isolated are 2 degrees cooler.

Not the result I had hoped-for.

R-134 source is a 30# bottle from eBay, made in India. Could be contaminated. Where do you source 152?

How does one know the R152 isn't impure, too?

Walmart's house brand of R134a is $8.88/12oz locally. I needed R134a in a pinch this weekend so I bought two (I have multiple 30# cans at home but I wasn't there so...). The result was very cold air on my S10.

Five cans of this would give you 60oz for about $50. Not as cheap as R152.

Compressor sounds good, positive clutch lockup and not abnormally hot.

Very good.

 

[1998_K1500_Sub]

R-134 source is a 30# bottle from eBay, made in India. Could be contaminated.

Have you used gas from that bottle in other systems, w/ or w/o success?

 

[Wildblue19]

Have you used gas from that bottle in other systems, w/ or w/o success?

I had used it when I rebuilt my wife's 2002 Ford escape system 6 months ago. Hers cools better than mine, but not by much, with a average delta on the highway of 35. She drives much less so I have not had to deal with many complaints.

The rear fan was on high, yes.

My 134 will not ignite and extinguishes flame when it interacts.