odd compressor humming, what is it?

[ellsworth]

i built my first phase change system this summer and it is great, i am using a window ac compressor with propane. on my test setup without the computer on which means no load put on the evap my compressor will start up and sound normal. after a min or 2 when it is sub -50c it starts to make humming sounds that get loud and then normal every second or so on top of the normal humming sound, some of the sounds are louder than others. also my compressor gets very warm, somewhere between 45c and 50c usually, how hot can it get and still operate safely, i have 200cfm blowing across it. the humming sound doesnt start untill it has been running for a while and the evap is very very cold, could this be the cold vapor return making a sound when it enters the compressor?

here are some temps for gary or bowman or aenigma or whoever needs them:

compressor outlet: 45c
condenser intlet: 45c
condenser outlet: 28c
evap: sub -50c (temp probe stops at -50c)
compressor inlet: 4c
compressor temp measured on top: 45c-50c
area around compressor inlet: 38c


maybe its just me being nervous with propane in the system
:banana:

[TheDude]

There's 17c difference between condensor in and out temps.....could it be excessive pressure on the high side?
Is the return line to the compressor iced up?
Does it go away if you put more heat to it?
Do you think it might be overcharged?

You probably know more about this than I do ellsworth, but that's all I can think of. You should have good air flow with that fan.

[Gary Lloyd]

What are the air temps entering and leaving the condenser?

Your compressor temps are normal. This varies considerably. Some run as high as 70C, although 60C or less is typical. A cold compressor is a very bad thing.

Your discharge line temp is 45C, which is good. This must not exceed 100C, and should in fact be far less. Sounds like the system is properly charged. :D

[ellsworth]

air in is around 25 and out is around 28-30. if i added any more refrigerant my high side would get very high and my low side would be wimpy so i dont think i am overcharged, im getting 4.5 feet of my suction pipe frosted with no load and the frost stops within a few inches of the compressor inlet. the heat from the compressor warms the pipe enough so that the actual 4 inches of pipe leading to the compressor stay above the freezing point. when i do put a load on it this frost will go away im assuming. thanks for the help, i guess i will just accept that ac compressors are niosy hehe and aenigma told me that the occilation of sounds is the compressor working in a vacuum wihch ac compressors arent paticularly designed for. woops big lightning, time to shut it down! later

[ellsworth]

another thing, the reason for the huge 17c temp difference in my condenser is because i have 2 120mm fans with 216 cfm blowing over the double row condensing coils. i think i can back off a little on the airflow but i need to make a voltage controller that will handle that much current, maybe a pwm of some sort.

[TheDude]

Sounds sweet....got any pics? :D

[ellsworth]

but of course :toast:

[ellsworth]

more

[ellsworth]

one more...oh and before anyone asks that is a nickel ontop of the evap. i just put it there to see how fast it would frost up hehe.

[TheDude]

Thanks man! Very nice! :D

:toast:

[Gary Lloyd]

another thing, the reason for the huge 17c temp difference in my condenser is because i have 2 120mm fans with 216 cfm blowing over the double row condensing coils. i think i can back off a little on the airflow but i need to make a voltage controller that will handle that much current, maybe a pwm of some sort.



You have a 3-5C difference between condenser air in and air out. That shows you have more than enough airflow. Keep that difference below 10C and you're good to go.

When the compressor hums, does the amperage draw on the compressor go up?

The system is looking good, except for all that ugly white stuff. Ewwwww... frost sucks. Insulation is our friend. :D

[bowman1964]

yep check that amp load when the humming starts...could be the compressor is on its last leg if the amp's increase after startup and the humming starts.


but i do like you setup,that will work great to bench with..:D

[ellsworth]

i bought the compressor new so it would be hard to imagine me wearing it out so fast hehe. ill check out the amperage, its made this sound from the first time i started it up and got cold so i think ill set my mind at ease.

oh and im all insulated up now hehe, no more white grossness.

[ellsworth]

ok i should have done this sooner...i went outside to listen to my house ac unit which has a 32,000 btu reciprocating compressor much like my own only over 6 times bigger, and noticed the same interharmonic humming that varied in intensity. the only difference in the sound of the home ac and my computer ac is the much lower pitch, similar sounds. *slaps forehead*

oh and bowman i plan on benching alot, i think i have found a new addiction! ive got a modded 9500np with an 80w pelt just asking to stressed from 3dmark2001 and maybe a new 2500 on its way.

edit: bowman you need to get back to benching! i cant wait to see that cascade setup. i myself have put in some thought for makeing a dual evap single stage phase change for a dual athlon64 setup once they get going. that would be amazing...maybe next summer, i already have a 10,000btu compressor for it. if you get into benching maybe you can setup your multiple evaps to cool a dual a64 setup. i think they will be very competitive later this fall in the orb.

[Popcicle]

Dang nice unit there bud.

Any chance you could tell me the
size and length of the cap tube?

I have a propane unit under construction.

Appreciation.


Pops.

[ellsworth]

it uses 11ft of .026" cap tube. glad to help out :toast:

[Popcicle]

And I thank you from the NW San Antonio area.


Pops.