PDA

View Full Version : noobie question re testing compressor







aaron cadell
13-09-2002, 02:11 AM
Hi,

I've got a fridge that indicates it has a faulty compressor starter relay.

Its a nice and clean looking compressor, and extraction of the relay from the compressor body leaves two clean poles exposed.

I want to test the compressor for function.

My intention is to connect a phase to one pole and a neutral to the other pole for a short period (> 1 minute)

... Is connecting phase and neutral to the 2 relay poles an appropriate method for testing the function of the compressor??

Best Regards,
Aaron.

Gary
13-09-2002, 07:50 AM
No, it is not. Don't do it.

aaron cadell
13-09-2002, 11:16 AM
Hi Gary,

Why not? ..

I assumed that the compressor would draw as much current as it required to run the compression and that the relays role is just to distribute current to the peripheral appliances (e.g. lights)... therefore bypassing it seemed logical..

How should compressor function be tested if the relay is suspect?

Regards,

Aaron.

Gary
13-09-2002, 12:18 PM
That is not it's role. You obviously have no idea how a compressor or it's starting components work. You are going to destroy the compressor and hurt yourself.

superheat
13-09-2002, 01:28 PM
That compressor realy has two motors in one. You are in effect wiring those two motors in series. one minute is long enough the burn the compressor up. Replace the defective parts exactly the way they were. If the compressor does not start, you can try to destroy it then are call someone who know what they are doing.

Electricity is not something to play with. People have died trying to save a few bucks. You might want to check your local library to learn more about what you are working on before you just start connecting wires to something. Time-Life books are pretty good.

aaron cadell
14-09-2002, 08:55 AM
Thanks Gary. You are right i had no specific knowledge about how the compressor works. But now i know that there are two motors and by wiring directly through the two relay poles i would be running both motors in series which could be very dangerous to the health of the compressor.

I'll do a bit more reading..

aaron cadell
15-09-2002, 03:22 AM
One thing tho on the way .. what surprised me most at first was that there was no fuse. Is the duty cycle of the fridge to hard on fuses or is there some other good reason?

superheat
16-09-2002, 01:32 PM
The induction motor for the fans are inerantly protected, very hard to burn out if it does not start. The compressor has a thermal overload for protection. Fuses are to protect the wiring and prevent fires.

aaron cadell
16-09-2002, 06:48 PM
Induction motor.. thats sounds good!

I don't think theres any fans on this model though. just the sealed compression unit with five sections of copper tubing extruding from it.. One of those tubes is clearly a sealed piece of short tubing used for adding coolant.

the motor unit is a

Model FN66001G
220/240V 50Hz AC Only 1PH
Full Load 0.96A CCL2F2
Matsu****a Electric
Singapore

And the refrigerator unit is a Simpson moist/cold 411 that stands about 5 1/2 feet tall.

I wonder why the whole compressor unit is so well sealed.. I saw a cutout version showing internal detail thru a shop window and the internals all looked like sealed units anyway.. is there some obscure safety issue about the sealing of the compressor cases?

FreezerGeezer
19-09-2002, 12:53 PM
Hi Aaron

With all due respect, it's obvious that you have never worked on this sort of equipment. Please please pay a professional to deal with it. The chances of hurting or even killing yourself are just too great.
Some other unqualified bloke actually blew himself up earlier this year doing a very similar job to what you have there, on a similar size unit. I seem to remember that other people in the area were also hurt.
It's just not worth saving a couple of hundred bucks!

aaron cadell
19-09-2002, 03:09 PM
True!

Thats good advice freezerGeezer..

What in the fridge explodes BTW??

FreezerGeezer
20-09-2002, 08:36 AM
Hi Aaron

It was a chemical Oxidisation explosion, if I undestood the article properly. The idiot used the wrong gas to pressure test his brazing. The right way to do this is probably the first thing you learn as a frige tech./engineer, right after how your gaffer likes his tea. Do it right, and it's safe.
Add this sort of stuff to being licenced to work on flammable gases (for rooftops with gas fired heaters, for e.g), and you begin to understand that in fact, a good frige tech. is NEVER expensive.
And that gets us back to the age-old whinge about pay & conditions in engineering.

zolar1
20-09-2002, 06:58 PM
Try looking at this site:

http://www.johnstonesupply.com/main/OrderNow.asp?store=0102&browse=yes&category=12

It's a hermetic compressor analyzer.

Part number H24-355
Mfr number HA1

It usually retails for around $240.00 (US)

THat should make things both easier and safer...be sure to exactly follow the directions.

When in doubt, seek someone with more experience on how and what to look for.

Most small hermetic compressors should draw about 2 - 1/3 full load amps, but check with the comp mfr for exact ratings.

aaron cadell
23-09-2002, 02:38 PM
Hi Zolar,

1. 2.3 Amps at 120Vac? (We use 240V in New Zealand.)


2. what exactly gets damaged in the compressor if i connected Phase and Neutral to the relay poles through the compressor case? (I accept that it is not advisable but I have this need to know just what would happen..)

3. Why particularly is the compressor case sealed ? (I recall seeing other compressors that are not sealed units and wonder what design feature makes it so..)

DaBit
10-10-2002, 01:29 PM
Originally posted by aaron cadell
1. 2.3 Amps at 120Vac? (We use 240V in New Zealand.)


Nominal current draw of the compressor depends on operating conditions. Startup current draw is way higher. Anyway, if the current draw of your compressor exceeds 3 amps @ 240VAC, there is definitely anything wrong. If it stays below 3 amps, it might be OK, but you will not be sure.



2. what exactly gets damaged in the compressor if i connected Phase and Neutral to the relay poles through the compressor case? (I accept that it is not advisable but I have this need to know just what would happen..)


The compressor probably has a Run and an Start winding (3 connections on the compressor). If you connect 240VAC to the common and Run, the compressor will make noise, but it won't start. After a few seconds you either burn the windings (less likely) or the thermal protector kicks in (more likely). If you connect 240VAC to the common and Start, you burn out the start winding. If you are lucky it takes 10 seconds, but it might as well happen in the time you need to blink your eyes.

If you definitely wants to play with it (I do not recommend it sicne you obviously have no idea what you are doing), I would say: connect the neutral to the common, phase to the Run winding, and a capacitor of approximately 5uF/400VAC between phase and Start. Now, to start the compressor, connect a capacitor of ca. 20uF/400VAC between phase and Start. Do this only for a few seconds.


3. Why particularly is the compressor case sealed ? (I recall seeing other compressors that are not sealed units and wonder what design feature makes it so..)

It is sealed so that during the lifetime of the refrigerator almost no refrigerant will escape. A refrigerator is a critically charged system, thus it's working depends on the proper refrigerant charge. If refrigerant leaks out through seals the efficiency and performance will drop.

aaron cadell
10-10-2002, 11:22 PM
Thank you DaBit,

thats exactly the kind of detail i needed to know.

Regards,

Aaron.

zolar1
31-03-2003, 07:32 AM
On a further note-

If you double the applied voltage, the applied current should be halved. Watts are watts.

DaBit
31-03-2003, 10:06 AM
It's not that simple, and only true if the windings in a motor would form a theoretically ideal coil. They do not, so in realty back-EMF from the coils rotating in the magnetic field is not able to keep up with the increased voltage, and the windings will overheat.

bernie
12-04-2003, 04:59 AM
Just checking,
Anyone heard from aaron lately?????????????
Hope he's ok

Brandon
28-04-2003, 08:37 PM
Lets just hope he doesnt have access to oxygen if a leak were to occur.