Hermetic compressor

Hi

I've been called to a display chiller (made by Frigor Pastor). The compressor is starting up, and running for a couple of seconds, shutting off, with a squeaking noise. I've checked the system over and noticed that one of the two condenser fans is not working, due to a bad fan motor. It's on R22, and the pressure is 120psi on compressor start. The HP starts to rise (not by too much) and the LP drops, as expected. When the compressor trips off, the pressures equalise.
I've put it down to the compressor going off on internal relief, being caused by the broken fan causing condensing problems.
Any other opinions ?

James

Quote:

---

Originally Posted by iceman007

Hi

I've been called to a display chiller (made by Frigor Pastor). The compressor is starting up, and running for a couple of seconds, shutting off, with a squeaking noise. I've checked the system over and noticed that one of the two condenser fans is not working, due to a bad fan motor. It's on R22, and the pressure is 120psi on compressor start. The HP starts to rise (not by too much) and the LP drops, as expected. When the compressor trips off, the pressures equalise.
I've put it down to the compressor going off on internal relief, being caused by the broken fan causing condensing problems.
Any other opinions ?

James

---

Are the two fans in separate fan shroud chambers, or do they share a common chamber? If they share a common chamber, then the working fan will pull air through the non-working fan blade, instead of pulling air through the condenser. The effect will be as if no fans were working.

hi iceman007,

it must be a small unit, so change the bad fan, restert, if trips again, replace compressor.

if high pressure controll not present, install one with manual reset.

chemi :)

Quote:

---

Originally Posted by iceman007

Hi

I've been called to a display chiller (made by Frigor Pastor). The compressor is starting up, and running for a couple of seconds, shutting off, with a squeaking noise.

James

---

Pardon me if you've checked the obvious already, but if the compressor truly runs for only a couple of seconds and it is single-phase, check the start relay to be sure it is dropping the start circuit out. I assume the fans keep running?

Another possibility, admittedly remote, but one I found once was that the fans had been wired for continuous operation and the compressor was shutting off on low pressure due to a low charge. Same symptoms as you report.

To confirm your internal trip diagnosis, did you check for voltage at the compressor terminals during the trip? Ammeter on the start circuit to confirm relay operation?

I would be very surprised if the fan has anything to do with the problem because you state that the condensing pressure rises ony slightly.

What are your diagnostic procedures for something like this?

Rog

Quote:

---

Originally Posted by RogGoetsch

To confirm your internal trip diagnosis, did you check for voltage at the compressor terminals during the trip? Ammeter on the start circuit to confirm relay operation?


Rog

---

hi rog,

pardon me,
what kind of ammeter you use to check the voltage drop that works so quick?

just today I got stuck with a big split that stoped working two seconds after compressor start.

checked everything, but could not find anything wrong.
when I've tried to check voltage drop on start, my digital Clamp amperemeter (TES) could not read the drop quick enough so............. I've connected a tv set paralel to the unit knowing that the screen shot if voltage drops below 185V.
and.......bingo, it shot it self.

some idea, but worked fine.

chemi :)

Must remember to go down Currys and buy a TV :D (English humour Chemi :D )

Frank

you will get it cheaper at argos :D

chemi

This chiller had not been serviced for a long time. Compressor replaced. I would have thought that the one fan had not been working for some time, and caused excessive head pressure to ruin the compressor. Thanks for the help.

James

Quote:

---

Originally Posted by chemi-cool

hi rog,

pardon me,
what kind of ammeter you use to check the voltage drop that works so quick?

chemi :)

---

Two different tests referred to here. I will simplify for those new to the field. If any of this is new to anybody, please buy Gary's book!

Iceman did not seem sure of his diagnosis of the unit being off on internal overload. To verify this, I advised checking voltage at the terminals after the unit had tripped out, in order to verify that nothing else was stopping the compressor.

True, I can't get an accurate reading of start voltage or amps if the unit is starting correctly, since start takes less than a second, but if the unit runs for a couple of seconds, as Iceman said, this is plenty of time to see if start amps drop off or not.

If the start circuit does not drop out, the internal overload will open in a couple of seconds. I see exactly this symptom frequently on the small, commercial, single-phase units I usually service. I carry the most common relays and capacitors and sell more of them than compressors.

If it is a low-torque start with no relay but only a run capacitor in the start circuit, the same test initially will diagnose a shorted run capacitor or an internal short to ground which I would verify with my capacitor tester and a continuity tester between the compressor body and the compressor terminals with all leads removed.

Then I would also check amps in each lead as well and ohms in each compressor winding for both single and three-phase units.

My UEI multimeter is fast enough to show some voltage depression on start, but not accurately. That is not usually a concern and when it has been, I have used a separate wiring harness as a bypass to test the compressor. But I usually just look at start amps in a case like this to see if they drop off in a second or less.

I used to use my ancient analog meter for this kind of test because the needle responded quicker than my digital but since it died, I have not tried to replace it.

Finally, I would not expect the failure of one fan to kill the compressor unless the ambient were high and the customer had failed to notice repeated compressor overload trips, perhaps for many days or weeks. The first heat wave of the summer usually has me called out for all the units that have been operating all winter on a single fan.

Rog

Quote:

---

Two different tests referred to here. I will simplify for those new to the field. If any of this is new to anybody, please buy Gary's book!

---

What the hell, buy my book anyway. :D