The Homemade Heat Pump Manifesto

[AC_Hacker]

dremd,

> WOW man
> MAD props!

Thanks, it was a ton of work (actually 8 tons of work)!

Originally Posted by dremd

WOW man
If you are going for cheap - Harbor Freight Tools - Quality Tools at the Lowest Prices is impossible to beat; you will need a big air compressor to run it; but if you are doing this , once per year you could borrow one . . . mine pegs my automotive HVAC A/C gauge every time.

The manifold gauges get non-linear near the end of their scale which is very unfortunate, because we really need to know what is happening at that end to be successful.

I found a very useful link to vacuum equivalents here:

Vacuum Pressure - Converting Units

...probably a good idea to bookmark AND print it out and tape it to the inside of your HVAC tool box (I have one in mine).

The venturi-type vacuum pump you linkled to (HF #96677) is able to hit 28.3" of mercury at sea level. So this would be 'Inches Mercury Gauge' on the chart. Notice that this is around 94.8% vacuum. For HVAC work, we need to pull down to at least 80 microns (99.995% vacuum) and hold it there for a while to let all the moisture that may be in the system turn into vapor and get sucked out by the vacuum pump. It's true that the venturi-type vacuum pump may peg your manifold gauge, but the extra vacuum is where the de-moisturization magic happens.

The micron gauges use the principle that heat dissapates very poorly in a total vacuum. The gauge has a tiny heater and a tiny thermocouple together in the space that is getting vacuumed. While there is air, etc in that space, the heat dissipates well. As a vacuum is approached, the heat dissipates progressively less well, and the temperature rises. The thermocouple measures this heat rise and turns that data into vacuum readings.

The other pump you linked to (HF #66466), the Two Stage 3 CFM Air Vacuum Pump would work just fine.

Might want to keep your eye peeled for a good micron gauge to show up on ebay. I bit the bullet and bought one new.

Best Regards,

-AC_Hacker