Air Conditioning - Walk in Refrigerator problem

I'm a refrigeration tech at a hotel and I have a walk-in refrigerator unit where the original copeland semi hermetic compressor froze up (14 years old) so we replaced it. After replacing with the same type of compressor as the original with all new starting and runnning components, it started up fine and we began to fill with 22. It ran for approximately 5 minutes and then the Start Cap popped. We figured bad potential relay, so we replaced the relay. The new start cap popped again after 2 minutes running. We Called the refrigeration shop where we purchased the new compressor and according to them all of the start components are correct. We quadruple checked incoming voltage and the wiring to the start comonents and compressor and everything is wired correctly. We've replaced the potential relay and start cap 4 times. But every start cap we put in keeps popping.

To my understanding the relay is supposed to take the start cap out of the circuit, but it's acting like it doesn't because it keeps popping. We even called an outside refer company to troubleshoot and they're condeming the new compressor. My question is how can the compressor make the start cap pop when theoretically it's not supposed be in the circuit? We already have a new compressor coming in, but I'm affraid it's still going to do the same thing. Any feedback is appreciated.

Mahalo

Out of the box here. Are you for sure its the right potential?
Is the amp draw right for the compressor on start up???
System clean no noncondensables, TXV ok? Does it work off pressure control or tstat and solenoid and is that clean and open???? Did you Ohm out the new compressor and is it ok? I have had new compressors with a very small short inside it ;)

Does the start cap have a bleed resistor to drain the charge after the pot takes it out of the circuit.

Just a thought

Thanks for the reply. According to our supplier all components we have is correct and to manufacturers specs. So we do have the correct parts.

The unit is running of a t-stat & solenoid in the box, and low pressure control at the compressor. The solenoid & TXV is working propertly because for the short time that it stays on the pressures look normal at start up. Amp draw at start up is a little high (which is normal) but not excessive and does drop while running. It's a simple relay. terminals 1 & 2 = contact and terminals 2 & 5 = coil. We know it's electrical but it's been pretty tricky and not to mention frustrating trying to figure this problem out.

CiiTech,
The capacitors do not come with the resistors and we had to purchase them seperately. But yes we do have bleed resistors on every start capacitor..... but they still pop.

just for the heck of it, what is the model and serial number of the compressor?

Ciitech,

I don't have that info with me right now but as soon as I do I'll post it.

Thanks

Ciitech,
Here's the info on the compressor.

Brand: Copeland
Model: KAEB 007E CAV 800
SERIAL: 07E65575R

RUN CAP: 10MFD 370V
START CAP: 145-175MFD 250V

THANKS

http://download-v5.streamload.com/638dc4a2-d4e2-47f2-9bf1-fefaa288a2d1/ciitech/Hosted/KAEB%20007E%20CAV%20800_Wiring.pdf

Copeland did not give specifics about start and run caps for this compressor.

The start capacitor kit part number is 914-0008-51
The run capacitor kit part number is 914-0037-04

I got those numbers from the service parts page for this compressor. here's the elecrtical components page:
http://download-v5.streamload.com/638dc4a2-d4e2-47f2-9bf1-fefaa288a2d1/ciitech/Hosted/p2jcvOQiunHEUFm3BdmpWlcOPICElectComp.pdf

Condensing unit model may help but I think it will only give more Copeland part numbers.

Ciitech,
Thanks for the feedback. The scematic you sent is correct and it is wired up exactly as shown. If our relay is really opening when its supposed to be, I can only see the start cap popping if it's somehow feeding power back to the start cap from the run capacitor. ???????????? We're still waiting for the new compressor to come in. Hopefully it comes in by tomorrow. Thanks again.

Did you Ohm out the windings in the compressor? Are they what they should be??

Ed Imeduc,
Yes I ohmed it out.
Start and Run 6 ohms
Start and Common 5 ohms
Run and Common 4 ohms

Also checked case ground and no short.

I figure at a hotel this would be a 230 volt compressor, but have to ask if it's 115 volts. If it's 115 is nuetral on the "R" terminal?

Do you have another start cap to perhaps pop?

If so can you try starting the compressor and take some voltage readings?

Since it looks like you'll have 2 minutes tops you'll have to do this pretty quickly. Might want to have someone standing by to kill power for safety and as soon as you get the readings.

After the compressor comes up to speed, say 10 to 15 seconds, what is the voltage between "C" and "R" and "C" and "S" (or "C" and terminal 2 on the pot relay)?

Watch your meter as if this is a 230 volt comp "C" and "S" voltage can be 400 or more.

I'm getting a feeling that we are not only looking for the cause of the current problem but also for what took the original compressor out in the first place.

Ciitech,
It is a 220V system. The replacement compressor finally came in. Replaced compressor and potential relay that came with it. Vaccumed, Charged and started it and monitored pressures and amp draw at start up and running. Perrrrrrrrrrrrfect. The first replacement compressor must have been faulty. Thanks for all the feedback everyone I really appreciate your expertise and input.

Aloha and Mahalo!