Vacuum pump vs air purge

[Acrisoft]

Hi

I know vacuum pump is the right tool and I have one.
But I would like to know who ever used air purge method to install split ac unit and
if the unit was able to run normally for at least 3 years.

Also, if is it possible to apply it to R410A units and for units larger then 18.000 BTU.

Moises

[frank]

There are at least 2 things wrong with purging air from a split system.

1) You have no way of knowing if you have removed all of the moisture
2) You are left with a refrigerant charge that is less than the recommended amount.

How long will a system run for with a short gas charge and an unknown amount of moisture in the system? you may as well ask 'how long is a piece of string'

If you have a vacuum pump, why not use it and do the job properly?

[Acrisoft]

Good answer, Frank.

It's only for pure knowlegde purposes. I live in Brazil where this issue is not completely regulated (2013)
and many people insist in installing it by only air purging.

"You are left with a refrigerant charge that is less than the recommended amount. "

If the installation is short ( something as 3m long) would it still be a problem ?

I would like also to get more opinion of techs in other countries all over the world.

Moises

[frank]

If you have a pre-charged split system and you purge the lines, 3m of pipe or 30m of pipe, how do you know how much of the charge remains in the system?

Any system, split or otherwise, running on a short charge will give poor performance, and, depending on the amount of undercharge, may lead to the compressor running 'Hot' which will shorten it's life.

[Acrisoft]

OK. Talking about short charge, some systems are made to work from 3m to 7m long and I think this 4m difference would be a reserve, if only 3m of pipe is used. Or the amount required for purging is more than I imagine ? I am not defending to skip the vacuum pump and not discussing the moisture issue. Only trying to understand how a system is projected to work from 3m to 7m without adding more refrigerant.

[kefah]

frank is right
as i red in most of the split unit manufacturer installation manual
they assumed that u can use purging air method in new installation with R22 only
and they assumed that u must use vacuum pump only with other refrigerant such as R410a

[still learning]

in france there is for sale some small splits . just hole thru the wall and about 7 meters of pre flared pipe . the instruction manual shows purging the lines on the outdoor flares
i would thought france would ban the sale of these.
still when i fitted it . i used my vac pump and torr gauge. no gas loss of a blend ( 407c).
and know i have followed the correct manner of install . and not vented gas .
and hope the owner of the unit will have a trouble free use of the unit for years .

it was a non payment job , but enjoyed nice wine and spirits and great food and good company .
i quite like barter.

[frank]

in france there is for sale some small splits . just hole thru the wall and about 7 meters of pre flared pipe . the instruction manual shows purging the lines on the outdoor flares
i would thought france would ban the sale of these.
still when i fitted it . i used my vac pump and torr gauge. no gas loss of a blend ( 407c).
and know i have followed the correct manner of install . and not vented gas .
and hope the owner of the unit will have a trouble free use of the unit for years .

it was a non payment job , but enjoyed nice wine and spirits and great food and good company .
i quite like barter.

Good Job....I wish I could do jobs for Wine :D

[install monkey]

if your gonna use a vac pump, get a torr gauge too- do a proper job;)

[NewmanRef]

Do people really still purge?? I've seen it done as an apprentice at o'clock on a Sunday night 200 miles from home but I didn't realise people were out there putting in splits and not even owning a vac pump?

[Jeremy Martin]

A former coworker of mine did mission work in Liberia for four years. He said the guys there didn't know what a vacuum pump was; they'd purge and go.

He also said they replaced compressors pretty often.

Manufacturers of inverter systems say charge is very critical, and I've found that to be true. A little low on charge, and they'll lock out on low pressure in cold weather. Probably won't have that problem in Brazil. Still won't be efficient, and may run high superheat which, as Frank said, could cause the compressor to overheat.

Energy savings and longer equipment life will easily offset the cost of doing the job right, and then some.