Charged through manifold with both hi & low valves open

[Czissman]

Hey folks, I replaced a leaking high side schraeder valve on my '99 Silverado 1500, and then used a manifold to recharge the system after drawing a vacuum for about an hour. However, whenever I charged it, I opened both the high and the low side valves on the manifold and I understand you're only supposed to open the low. Sooooo... What do I do from here? The system is actually working nicely.

[JohnHere]

What did you use to charge it, small cans or 30-pound cylinder? I hope you charged it with the compressor turned off. Otherwise, you risked the can or cylinder exploding with the HP valve open. Obvious severe danger to yourself as well.

You mentioned that the system is now working okay. What are the pressures at ~1,800 RPM, max A/C, blower on high, doors/windows open, and ambient temperature noted when testing? What is the center vent temperature?

Surprised you got enough refrigerant in there like that.

[Czissman]

Thanks John, for your help!

This should have been a simple task, but I managed to screw it up. I'm embarrassed to admit that I also had the hoses attached backward (low port to high gauge, high port to low gauge), so I was in fact charging the low side after all. I was in a hurry, and I doing something I'm not familiar enough with to be rushing as I was.

Here are the answers to your questions.

What did you use to charge it, small cans or 30-pound cylinder

I used small cans.

You mentioned that the system is now working okay. What are the pressures at ~1,800 RPM, max A/C, blower on high, doors/windows open, and ambient temperature noted when testing? What is the center vent temperature?

70-degrees ambient. approx 378-psi low, 200 high. 56-degrees at center vent.

The low-side static pressure was around 30.

It seems to be there's a little room for improvement in the cooling effectiveness. Would you agree? What would you suggest I do?

EDIT: when operating at the hire 1800ish RPM range, I could hear the compressor cycling off and on periodically, but it still provides cooling. Will this be caused by air in the system? If not, what do you think might be behind it?

Appreciate your help in advance!

[JohnHere]

This should have been a simple task, but I managed to screw it up. I'm embarrassed to admit that I also had the hoses attached backward (low port to high gauge, high port to low gauge), so I was in fact charging the low side after all. I was in a hurry, and I doing something I'm not familiar enough with to be rushing as I was.

Live and learn. Since you're somewhat unfamiliar with Mobile Vehicle Air Conditioning (MVAC), be sure to ask before proceeding with repairs. There's a vast knowledge base on this Forum, and members—many of whom are experts in the MVAC profession—can offer valuable advice. I'm relieved that you charged it through the low side after all.

70-degrees ambient. approx 378-psi low, 200 high. 56-degrees at center vent. The low-side static pressure was around 30. It seems to be there's a little room for improvement in the cooling effectiveness. Would you agree? What would you suggest I do?

It would be best to wait until the ambient temperature in your area rises to 80°F or higher before doing MVAC diagnostics.
Even at the 70°F ambient, it seems that the pressures and vent temperature you posted are "off," though. Let's review. For a correctly operating system at an ambient temperature of 70°F, typically, the HP side should be at or about 185 PSI and the LP side should be around 30 PSI or a little lower. The center vent temperature should be in the low-40°F range. Obviously, you're not achieving that, but why not?

Chances are, you don't have the correct amount of pure refrigerant in the system. I say "pure" because some of the small cans sometimes contain additives, including sealer, which will cause additional problems that are difficult and costly to repair. Check your cans for sealer.

As to the amount of pure refrigerant, there is only one way to charge an MVAC system, and that's by weight using either an accurate purpose-built scale or a Recovery Recycling and Recharging (RRR) machine that professional shops have. You can do the job at home with a good electrically driven vacuum pump, a professional Manifold Gauge Set (MGS), a precise scale, R-134a, and (if needed) PAG refrigerant oil in the correct viscosity. Be sure to change the oil in your vacuum pump before you begin evacuating the system, and be sure to use only the correct vacuum-pump oil. Contaminated or old oil in your vacuum pump will result in a poor evacuation of all the air and moisture that might be in the system. And of course, start with a completely refrigerant-recovered system beforehand.

In this instance, double-check to verify that your MGS is correctly connected to the system and that the hoses are connected to the corresponding MGS gauges, and then re-post the pressures.

... when operating at the hire 1800ish RPM range, I could hear the compressor cycling off and on periodically, but it still provides cooling. Will this be caused by air in the system? If not, what do you think might be behind it?

That's normal operation for a Clutch Cycling Orifice Tube (CCOT) system like your Silverado has. Still, the question remains, have you installed the correct amount of refrigerant into the system? According to the specs that I have, the amounts vary according to the model and compressor:
--32 ounces net weight R-134a and 8.0 fluid ounces PAG-150 — Standard Cab, with HT6 Compressor and with OEM Harrison Compressor.
--32 ounces net weight R-134a and 8.0 fluid ounces PAG-46 — Standard Cab, with Denso Compressor.
--36 ounces net weight R-134a and 8.0 fluid ounces PAG-150 — Crew Cab, with HT6 Compressor and with OEM Harrison Compressor.
--36 ounces net weight R-134a and 8.0 fluid ounces PAG-46 — Crew Cab, with Denso Compressor

[Aungeliquema]

EXCELLENT thorough explanation! Thanks Johnhere