Vacuum range on HVAC gauge

[danski0224]

Really, no.

 

[cannuck]

While you might want to try a vacuum hold for a leak test it doesn't take into account the rate of evaporation of dissolved water being released from oil in the system. Few people seem to realize that reaching pressure to the boiling point of water it all doesn't just flash off to vapour in head straight for the pump. There are weak intermolecular forces (easily seen by measuring interfacial tension) that tend to make it difficult and slow to dehydrate quickly. You might get the absolute pressure down to some desired level, but water coming out of the oil or any other organic compound will increase the pressure, as will any increase in temperature. There is actually a way to calculate the shape of the pressure rise curve to subract a straight line (the actual leak) to differentiate from evaporative contribution. We do vacuum leakdown rate tests regularly, but in very large vessels with a LOT of hydrocarbons (oil wetted paper, varnish, etc.) to cloud the issues. The other thing is that in these deep vacuum systems, the pressure differential to cause movement of vapour to the pump is so small, the rate of flow can be glacial.

 

[LS6 Tommy]

These DIY systems are not leak tested for integrity as that defeats the DIY part, Not required by the manufacture. You sure can if you want.

Let me step back a little and clarify things. It all depends on what you mean by DIY. The only LEGAL DIY installations are ones with precharged line sets. The original questions were how to leak check and evacuate, which indicates the system is not DIY. Every non precharged line set manufacturer requires a pressurized leak test before evacuation. That what an integrity check IS. In a nutshell, all HVAC equipment that doesn't have precharged lines is technically required to be installed be certified individuals. The only thing you can DIY on them is mounting the units, running the line set and power. You can't legally DIY anything that involves refrigerant.

That being said, there are plenty of people here that are more than capable of doing DIY HVAC properly and I have no interest in making trouble for any of them. My intent is to help get our members good info, not to chastise them for taking on new skills.

Tommy

 

[KenC]

I'm really not sure how "N2 pressurizing defeats the purpose of DIY". You can rent a bottle of nitrogen for like $100 from a welding supply store, and a regulator is like $70. You don't need any special licenses.

Anyways, what we're ultimately getting at, is that it doesn't even matter if your manifold's low pressure gauge is faulty. Getting another manifold gauge to compare it against is pointless, because it's either way its the wrong tool for the job. You can get a basic TPI 605 micron gauge for about $110. It's the only way to truly tell if your vacuum is good enough.

When you're done, put the gauge on eBay for $80 and get most of your money back. That simple.

Or, just get the one somebody else bought and put on eBay. There's a few on the bay right now for 80 bucks or so.