Just ran up on two 3 phase compressors in roof top units yesterday evening. Had me chasing my tail when I saw pressures equalized on both units while compressor was running. An 18 wheeler had hit the main power supply at the back of the building and the business was running on a 3 phase generator. Most of what we deal are single phase residential units. After we left, my helper who had some industrial mechanic background got to thinking and told me it might be possible the generator phase rotation was wrong. This pretty much confirms it. We'll be going back today to swap phases. Thanks!
Here’s a tip involving some 3 phase motor concepts. Inverter mini split compressors are actually 3 phase wound, brushless DC motors. The outdoor unit will call for single phase 208/230 VAC. But with the inverter technology, the compressor will actually be a DC motor(which then can modulate system capacity via modulation of the level of voltage being delivered to the compressor motor…whereas AC voltage motors can only change speeds via modulating the frequency). Anyway, I am a licensed HVAC contractor in the state of FL, and I recently did some work on a new mini split system that was installed by someone else. They started the system up but forgot to open the service valves. Would not run in heat or cool. Shortly after attempting startup, it began displaying error code P4 (this is a Blueridge brand system sold by Alpine Home Air Products and manufactured specifically for them by Midea). I found out about the closed service valves and the error code after I arrived and began diagnostics. P4, in this, instance references an “inverter compressor drive error.” I tested everything that called for being checked out: wiring connections between the compressor and main PCB, continuity/resistance testing of the IPM, continuity/resistance testing all 3 windings of the compressor(remember it’s 3 phase, so all windings should measure of equal resistance), continuity/resistance testing of the reactor (reactor itself, isolated from the PCB, and the wiring between the reactor and the PCB), and I tested the outdoor fan motor(also a DC brushless motor)…all of these checks turned out within spec. The compressor checks out electrically, but it just would not start. It would try though. After resetting power to the system, and calling for cool or heat, the outdoor fan would start running and then the compressor would begin trying to start. After several seconds, the compressor would cease trying to start, the outdoor fan would shut off, and it would begin displaying the P4 error code. I figured the compressor was just stuck, mechanically, from being started and ran with the service valves being closed by the person that installed it. Well, knowing what I know about 3 phase motors, I knew that I could switch two leads at the compressor terminals, and apply power to the unit, and the compressor would run(or at least attempt to run) in reverse rotation. I switched the W(common) and V(start) leads directly at their termination on top of the compressor. Left U(run) where it goes. I turned power back on and waited for the thermostat to call for cooling. Outdoor fan started up and several seconds later, the compressor kicked on, running in reverse! As planned. I let it run for only literally about 2 seconds and I cut power right back off. Swapped the compressor leads back around for correct rotation. Turned power back on, waited for thermostat to call. And it started right up and ran beautifully. Saved me a huge headache. Little bits of knowledge picked up along the way can really come in clutch sometimes!
😅this video was helpful especially since im going to install a 3 phase 5 ton condenser unit tomorrow . Now im a bit more confident heading into tomorrows install.
@@TaddyDigest I really wish I could speak to you a really could use some good advice If you could please help me out would greatly appreciate it sir . Thank you Paul Allen
Just ran into my first 3 p stumped me with no cap but determined disconnect was faulty because arked after watching this video I can confirm that it lost a leg because the compressor would want to start but wouldn’t and when it was in suction was 35deg once I bypassed disconnect pressure were right on disconnect is coming in
480 3-phase is 277 VAC in relation to each hot wire / phase but 480V in relation to each phase comparing it to neutral. It's rather concerning to see your voltages below 460V, while you put a load on a 3 phase set, the voltage does drop but not THAT far. Just as 208 VAC in 3 phase is 415 VAC on each phase in relation to neutral. The real reason why 3 phase motors don't need a run capacitor / condenser is because the phase is at 120 degrees, whereas the other is 180 degrees out of phase and if you use one phase to power the compressor, you have to make up for the unpowered shift. The funny thing is the wiring technique used in Air Conditioners with US 240 VAC, which is 2 phases of 120VAC in actuality. When your supply power has to overcome the possibility of a deadlocking motor or at the very least the slowing down of it because of the load put on it. It further compounds the inefficiency of the whole system. It's too bad 3 phase power isn't available more in residential applications. For HVAC/R, Ovens, Stoves / Ranges and a couple of other high powered devices in the home should be powered by it. Because there's greater efficiency and uses a lot less power. Which means the savings are passed onto the owner.
I have a 3 phase walk in cooler roof top unit. I took it out of a 3 phase breaker box where each leg was 120v to ground. My other location is different it has L1& L3 120v to ground but L2 is 208 to ground on my meter. How do I wire this ?
