Evacuation

From Ted King Alpena, MI

Using a vacuum pump to remove air and moisture, is it necessary to use two tap valves for evacuation? I do, but a lot of service technicians don’t.

I know the cap tube is a small diameter device quite long in length. Can all air and moisture be removed from a low tap only? I’ve read articles that two valves should be applied to remove air and moisture from the entire system.

ANSWER:

By John Healy Past International RSES President Colorado Springs, CO

It is most important to use evacuation from both the high and low side at the same time. This method not only saves time, but also is more thorough. Yes, pull a complete vacuum by using two valves pulling from the high and low sides at the same time. It is the only way to completely prepare a system for recharging.

Freezer Fires

From Harold Heffert Bellmore, NY

I remember a question written some time ago about what to do after a freezer fire. My question concerns what precautions could have been taken to prevent the fire and whether adding nitrogen to the system would have prevented the fire.

ANSWER:

By Daniel Kramer, P.E. Patent Attorney and former chief engineer for Kramer-Trenton

I think adding nitrogen to the system to prevent what is a rare occurrence is not a good practice. Further, I’m not even sure that adding nitrogen would have prevented the fire. After all, I recall the system you mentioned as having R-404A, which itself is not flammable.

I once encountered a drier that got too hot to hold after it was opened. A drier manufacturer I questioned advised that the flames arose because the aluminum compressor bearings or pistons had been ground into a powder from too much liquid refrigerant floodback into the compressor.

The aluminum in pots and pans is coated with an oxide film. The film prevents any reaction with the air. However, when the aluminum particles reside in the drier, they have not been exposed to oxygen and, therefore, they have no protective oxide film.,p> When the drier is opened, the particles are exposed to the oxygen in the air. The oxidation process they undergo in forming the protective film raises the temperature of the drier.

In your case, maybe there was a felt pad on which the aluminum powder collected, and the oxidation of the aluminum powder raised the temper-ature of the felt pad high enough to cause it to burst into flame.

Publication date: 02/05/2001