AAON VFD Scroll Compressors

[kempdawg34]

Gents, Working on my first AAON VFD Drive Scroll Compressor, start up.

VFD=Yaskawa Z100 rated at 77amps
Compressor = Bitzer 380 Vac

Problem; The VFD Drive faults in a oL2 (Drive Overload)

During start up the VFD faults in oL2. Hand started VFD at 10hz, Compressor amp draw = 15amps, VFD amp reading = 48amps.
At 20hz VFD = 68 amps, actual amps at compressor = 30.

If I raise the HZ above 20hz the VFD Drive Over Loads.

I've talked with AAON and they think its a bad compressor
I've talked with Yaskawa and they're researching it

VFD Setup verified through AAON

Just FYI I have 2 units that are setup for VFD Compressors both units are doing the exact same thing

Anyone ever run into this? Any Suggestions?

[crab master]

What is the voltage setting the drives are set at? I'd assume 480, but the 380 compressor is throwing me.

There was a setting for 208 volt that you had to change from like H to I or something like that otherwise it would do exactly like what you are talking about. This was years ago so I am going strictly off memory.

Based on the info and past experience I'd bet this is a drive setting problem.

[air1]

You can't use a multi-meter to measure the current between the drive and the motor. You will get inaccurate results because it's not a true sinusoidal wave. http://support.fluke.com/find-sales/...00_ENG_A_W.PDF
Did you try reversing the rotation of the compressors?

[crab master]

Good point on the meter, but even if you use a true RMS you'd only potentially be off 20 to 30%. He didn't say he's using true RMS or exactly how he's measuring it. Hopefully he'll update. I'd call Yaskawa as well.

[Push It]

Does the drive have a bypass? You can run the compressor full out and check the amperage I would think.

[air1]

It is possible to have the load power from the VFD out of phase from the main power supplying the VFD. So potentially you could have the motor run in the correct direction when powered by the VFD and run backward when in bypass mode and vise versa. I'm just throwing out a WAG of the possibility that the scroll is running backwards, although it should have been tested at the factory if the VFDs were supplied by AAON. Another thing to consider is the possibility that you are single phasing the VFD. With single phase power (one fuse blown) The motor would still run because the VFD creates it's own 3-phase sine wave, but would get a over over current fault because of the loss of one of the power legs supplying the VFD.

[duke of earl]

Kempdawg,

I started up an AAON RNE120 this summer with 2 of these vfd compressors. I questioned the 380 volt compressors myself. One of the compressors was tripping off on compressor overload (one in peckerhead) so I called Yaskawa for support and come to think of it they never got back to me. I guess I should call them back to see if they forgot me.

[chesehd]

"although it should have been tested at the factory if the VFDs were supplied by AAON."

How many times has THAT phrase bit me in the rear? The Good Lord only knows!

Their QA has, in my opinion, gone farther down the tube with each passing year.

Great, beautiful, color wiring diagrams in each cover. Too bad the FACTORY doesn't use them during production.

Just my $.02 on that subject.

Ken

[air1]

Where are AAON manufactured? What issues have you encountered when working with AAON? I'm curious because I like the concept of their use of the digital scroll compressor for discharge air temperature control. Best control I've seen for a DX system.

[chesehd]

Sticking exclusively with the digital scroll units, it's been a year or two since the last one I've dealt with but the unit control wiring was wrong from the factory.

It's a great idea, no doubt about it, but roughly half of the units I've dealt with have had issues from day one and took numerous visits to correct. Other issues consisted of relays magically switching the heat on and latching until someone turns the unit disconnect off, units blowing the triacs off the DDC controllers and blaming the controls vendors, countless internal wiring errors, glob-job brazing...

But all of the units that had major or minor issues had a yellow tag Checked by: xxxxxx