88-94 5.7 Suburban A/C Diagnosis and Tuning

[cjcb1100]

Where did you pull the 60oz figure from? I really only charge 100% stock systems with specific charge amounts. Everything else I do by pressure, temperature and feel. By monitoring the evaporator inlet and accumulator outlet, when you hit the correct charge, it becomes very obvious. The lines get very close to the same temperature and the pressures drop on both sides of the system.

5 cans of 12 oz probably +- 15 oz

 

[cjcb1100]

Once you start changing the factory system, IE different orifice tube and a change in volume with a parallel flow condenser, factory specs become only a suggestion. I would think the refrigerant volume would be lower than 60oz, but you will have to read back through this thread to see recommended superheat values and operating pressures.

my system is all 94 specific except the pump the orifice shouldn't change charge amount since im trying to get closer to oem pressures is the same physical size as oem tube other than the id of the tube inside

 

[L31MaxExpress]

my system is all 94 specific except the pump the orifice shouldn't change charge amount since im trying to get closer to oem pressures is the same physical size as oem tube other than the id of the tube i

The tube absolutely will change the volume needed because it changes the gas/liquid volumes in the system at various points. The smaller the tube, the more time the refrigerant spends in the condenser, thus the more condensed/cooled the refrigerant becomes. That being said, we are talking ounces of change, not lbs. A 94-95 standard or extended cab with front only air calls for 36oz of R134a which is 2.25 lbs. 60 oz is 3.75 lbs. My 99 Tahoe with rear air only calls for 4 lbs or 64 oz. My 97 Van calls for 3.00 lbs (48oz) and an additional 1.25 lbs (20oz) for the add on rear unit for 4.25 lbs (68 oz) total. 60 oz is a gross overcharge of that front only system which is why I was questioning it and how you chose that amount. Using R152a a good starting point is 50% of that and it can need as much as 70% of that. My van has had good results using all I can get out of 4 x 12 oz cans of the alternative gas. Figure 1-2 oz of gas left behind or lost per can and that is 40-44 oz. Every system can be a bit different once you get away from OE specifications.

 

[cjcb1100]

i went off pressure r13a charts call for at that temp

 

[cjcb1100]

i dont know the sd7h15 has for capcity compared to the r4 i have no idea on that
also maybe the cans i just bough fresh from autozone could be under charged idk

 

[cjcb1100]

i dont see the orifice tube changing charge weight from oem if im now getting oem pressures on both sides? 40 psi and 175 at my temp is what it should be with the .072 tube my compressure must flow less so i had to go small to get that it was 45 - 135 or so

 

[cjcb1100]

Well figured a issue out, my pump rpm in gear at idle is 840 rpm taken with a laser tach i read it should be above 1200 rpm with my compressor

 

[L31MaxExpress]

Well figured a issue out, my pump rpm in gear at idle is 840 rpm taken with a laser tach i read it should be above 1200 rpm with my compressor

No GM compressor setup has a 2:1 belt drive ratio. Most are in the 1.25 to 1.5 range. Most compressors are limited to ~6,000 rpm continuous and maybe 7,000 rpm MAX during a downshift. Performance test usually call for the engine to be at 1,500 rpm.

 

[cjcb1100]

so a sanden will work fine at 840 rpm? internet says different

 

[cjcb1100]

thats @ 87 deg F and 5 12 oz cans of 134a some lost to bleeding air out of gauge lines

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im not being a jerk everything ive read says a sd7h15 like 1000-2000 rpm to be efficient and at idle in gear its hovering 800 rpm i am getting good temps if i increase the rpm to 1500 or so i do a lot of in gear idling