88-94 5.7 Suburban A/C Diagnosis and Tuning

[Wildblue19]

Great question @1998_K1500_Sub. I had to look at the bracket and think about it for a while when designing the mounts to come to the same conclusion - they are there to 1, center the bolts, and 2 transmit the load to the bracket without pinching the casting under the clamping force. I wonder if thermal expansion rates between the various materials is accounted for by them as well.

The upper 2 bolts are on the sliders and yes, they are employed same as factory. The bottom hole, well, I lost the slider. I did however shim the spacers with shim stock until there was 0 play to alleviate as much of the pinching issue as possible. I am much happier with how this came out and if anyone wants a bracket I have the files to make duplicates!

 

[Wildblue19]

Also, @L31MaxExpress the V7 has gotten me the best pressures so far of around 35psi at idle and 27psi around 2000 rpm. Pressure chart shows the 152 should be around 35° at the lower pressures but my vents are at 50-52F. I would say it's probably time to drop the dash and check seals and insulation.

 

[Wildblue19]

I let the system circulate and work for a few days and I threw the gauges on it today, things are looking good.

With the lowest pressure (essentially fixed) pressure control valve in the V7 and with the LPCO switch jumped it will suck the low side down below 18PSI around 2000 engine RPM.

I installed the adjustable low pressure cut off per @L31MaxExpress recommendation and I have it adjusted to shut off at 20PSI.

Pressure at idle: (70*F ambient 20%RH post hard drive and heat soak)

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Front superheat at 1.5*C. Rear superheat is 1.2*C.

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Vent temps are higher as expected than refrigerant, but acceptable. Around 40*F.

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I can't say I'm excited for the hot weather to return to South Texas, but I'm hopeful this is the solution I've been looking for since 2020.

 

[Wildblue19]

Follow up, mid 90s today and on the drive home was 38* front vents, rear vents about a degree or two colder. Lesson learned - there is no replacement for (compressor) displacement, regardless if sanden claims their enhanced compressor is up to the task.

 

[L31MaxExpress]

Follow up, mid 90s today and on the drive home was 38* front vents, rear vents about a degree or two colder. Lesson learned - there is no replacement for (compressor) displacement, regardless if sanden claims their emhanced compressor is up to the task.

Discovered the same thing with my Sanden experience on the 97 Express. Works decently on a single evaporator system, even works on a dual system ok up to about 85-90F outside, beyond that forget it. It just does not have the displacement especially idling around town.

 

[1998_K1500_Sub]

Lesson learned - there is no replacement for (compressor) displacement, regardless if sanden claims their enhanced compressor is up to the task.

Can you outfit a smaller pulley on the compressor, so as to increase the pumped volume per engine RPM?

... sort of like using the Sanden #4261 instead of the #4440, e.g., on L31 GMT400s, where the smaller pulley of the #4261 results in a ~17% increase in volume displaced vs. the #4440.

 

[L31MaxExpress]

Can you outfit a smaller pulley on the compressor, so as to increase the pumped volume per engine RPM?

... sort of like using the Sanden #4261 instead of the #4440, e.g., on L31 GMT400s, where the smaller pulley of the #4261 results in a ~17% increase in volume displaced vs. the #4440.

I had the 4261, I replaced it with a 210cc 10 cylinder HT6 replacement.

 

[1998_K1500_Sub]

I had the 4261, I replaced it with a 210cc 10 cylinder HT6 replacement.

^^^ Sanden 7cyl (#4440, #4261,…) is 155cc, so that HT6 is 35% bigger.

… but until they’re spinning “size doesn’t matter”.

Do you run the same pulley size on that HT6 as you had on the Sanden (you had the Sanden #4261 w/ 112mm pulley, IIRC)?

I’m assuming VE is comparable for both compressors, which is a stretch.