88-94 5.7 Suburban A/C Diagnosis and Tuning

[Wildblue19]

Plan of attack is to 1st add more refrigerant to my system, which is currently at 40oz of 152, and see if that helps. I already added some after our superheat discussion, from 35 to 40oz total, +/- a few oz due to losses from the can piercer. I am not hopeful that adding more 152 will work as I've tried it before, but it's cheap and easy. If it's not improved, I will remove my R12 rear TXV as a variable and replace it with the R134 one. Once that's done, I'll charge up to 30oz and then go about an oz at a time letting it stabilize in between shots and see where my sweet spot is based on pressures, vent temps, and superheat.

Also, it's worth mentioning that during my orifice tube testing I switched back to a new tube-fin style condenser. It is about twice as thick as the parallel flow one I had in, and the massive tubes probably have about 3x the volume of the parallel flow one. Since this is a more OE-correct style, I wanted to test it so that our R12->R134->R152 charge calculations were more accurate. Those calculations were assuming the system volume was as if it were factory configuration. In the tube-fin case, the system would have more refrigerant in it as compared to the parallel flow, so I wanted to test that as a variable. The results showed not much improvement. When I have the system broken open I might swap back to the parallel flow one.

 

[cjcb1100]

I am running the 11 blade and hd clutch and i know my blend door is closing i did it manually to test and i cheacked it out when i had the box appart foam was nice and pkyable surprisingly. Gona add a second aux fan and i am waiting on the red tube i noticed at idle i can head a shhhhhh noise from the evaporator like its pumping a boiling vapor liquid into it at higher rpms it goes away when ambient temps are below 90° thats why im changing to a smaller orifice my truck idles really low and ive never been able to figure that out i think it was tuned the iac keeps the idle steady with the ac but it sounds like its around 600 or so i have yet to get the chip burning stuff to read it and see whats in the prom i have burned them before just dont have the stuff at the moment i flash cb1100s in my spare time uses the same software to flash the proms

 

[cjcb1100]

so if i try the 152a what should my pressures be at say 95 degrees ?

 

[L31MaxExpress]

I am about to do a bit more work to my system as well. In addition to the high pressure cutout switch I have diagnosed as being the wrong one that hurts initial cooling around town, the rear expansion valve randomly hangs closed, resulting in poor cooling from the rear unit. The rear blower is still from 1996. It is weak and has bushing noise. Spal makes a replacement for the unit that is correct in every way. Finally I have determined that the variable orifice tube although it works great at idle and around town is wonky at high vehicle speeds. If I am cruising 70+ mph the compressor starts cycling very frequently on the low-pressure cutout causing the air to warm up to 50°F rather than cooling properly. I am going to start fresh with the correct rear expansion valve and the factory White orifice tube size and see where it gets me. If that does not provide acceptable results I have a Ford Red 0.062" tube that worked excellent in the past.

This is another piece of the puzzle on the variable and why I believe it is acting wonky. This was in 95°F with good airflow across the condenser. The pressures are extremely low and the pressures would read the same with a stuck closed expansion valve or plugging orifice tube screen. The variable seems to be going into the most restricted mode when the head pressures drop, further dropping pressures, causing the frequent cycling.

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[L31MaxExpress]

so if i try the 152a what should my pressures be at say 95 degrees ?

Depends on condenser airflow, engine compartment heat soak, interior temperature and heat load. I would say 180-250 psi. The more evaporator heat load and the less condenser airflow the higher the pressure.

 

[Wildblue19]

@L31MaxExpress cool diag on that system, let's hope that fixes your intermittent issues.

I was going through some AC parts websites and saw the opportunity to have some fun with my rear system; I have ordered a small (2.5"x6.5") receiver-drier and fittings to tie in to the rear system, in a bolt-on manner. I specifically got a cannister with a sight glass to (hopefully) be able to gather more data on the quality of refrigerant getting through the system. It'll be a while until I have time to break open the system and fab up mounts for the upgrade but I'm pretty excited to try it out and report back.

 

[L31MaxExpress]

@L31MaxExpress cool diag on that system, let's hope that fixes your intermittent issues.

I was going through some AC parts websites and saw the opportunity to have some fun with my rear system; I have ordered a small (2.5"x6.5") receiver-drier and fittings to tie in to the rear system, in a bolt-on manner. I specifically got a cannister with a sight glass to (hopefully) be able to gather more data on the quality of refrigerant getting through the system. It'll be a while until I have time to break open the system and fab up mounts for the upgrade but I'm pretty excited to try it out and report back.

My G20 is getting the ultimate rear ac upgrade soon. When I go through the front end and put it back on the road, I am putting a high capacity rear evaporator on a dedicated compressor with a remote condenser under the van. The auxiliary AC compressor bracket came with the 8.1L I bought out of a party bus. Set up for a Sanden/Seltec mounted backwards of all things. It is sticking out in front of the engine on the upper driverside, next to the OE compressor, bottom right of the picture. I am going to add extra insulation when I re-build the interior as well. Probably something sprayed in. I want a vehicle you can hang meat in, at idle on the hottest day.

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[L31MaxExpress]

This is going in the rear of the 83 van in a custom built console similar to what came in the van. It is smaller than you might think. 19" tall, 15" long and 8" wide. Evaporator capacity is 30K BTU which is very close to what a Sanden SD7H15 can deliver at highway speed. It is built by ProAir for a dash a/c and heater unit for a school bus. The van will keep the OE front evaporator system and it will have its own condenser and Vortec style Sanden SD7H15 as well. Then again if I can find a Serpentine clutch for an A6 (I know they were made), I may just use a single A6 and build a custom bracket to mount it to the HT6 bracket. An A6 can move over 42,000 BTUs. Single A6 would save me a ton of mony on compressors and they outlast anything modern 10 fold.

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[Wildblue19]

I am going to add extra insulation when I re-build the interior as well. Probably something sprayed in. I want a vehicle you can hang meat in, at idle on the hottest day.

I'm with you there. My truck needs paint and in a year or two when that happens it's going to get insulation and sound deadening for my audio system. My thermal camera shows a ton of heat through the floor boards and from the roof, and road noise washes out some low frequencies in my stereo at speed.

 

[Wildblue19]

While I'm waiting for parts, I'd like to ask if anyone knows the part number for the rear A/C (C69) evaporator line seal on the bottom of the air box? The one that the lines pass through out the bottom of the floor. I found the part number below, but it appears to be for 96+ trucks.

52469161​