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14 Posts
Discussion Starter #62
I was bored today so I did a little more testing. I wired the AC directly into a 50 amp plug to go right into the generator to see if I could rule out the 70ish feet of the cable running to my main panel as a problem. The air handler and the rest of the home was still using grid power.

Set the AC to cool and after the compressor kicked on there was approximately a 2-3 second delay before the fan turned on. Under grid power there is approximately a 1 second delay from the compressor turning on until the fan turns.

Even though the generator was literally right next to the AC I did not hear or feel any abnormal or excessive vibration/harmonic distortion that I previously heard a while back.

I was happy with the way the AC was running so I shut everything down and decided to test again from the other side of the house through the inlet box just to see if the vibration was still there. Surprisingly, while running the generator through the inlet box which has the AC approximately 70 feet from the main panel, the vibration and excessive noise that used to be there was no longer there. There was a small hint a vibration coming from the unit but nothing like it was a while back.

Again, I shut everything down and put the AC back to grid power and that tiny little bit of vibration that I noticed on the generator power was not there.

After thinking about it for a while I remembered a few weeks ago that I remove the grate on top of the AC to clean out some leaves that were in there. I guess repositioning the grate caused that noise to stop.

So now I wonder.... was this really a problem from the beginning or just a grate that was tightened down but perhaps sitting in an awkward position giving the appearance that the whole unit was not responding well to generator power. But remember, there is a tiny bit a vibration felt through the unit right now that is not there using grid power.

Nevertheless, at the moment it appears that my issue was related to a grate that was giving a false impression of a problem that actually wasn't there. That's just an assumption right now but I hope that's the case. However, I will be buying the soft start to lower that initial startup average even more

Premium Member
270 Posts
My 3.5 ton unit reacted the same way with my eu7000. In my case my AC unit is old and tired. My inrush Numbers exceed the nameplates LRA. LRA is 110amps my unit tests at 130amps and soft start dropped inrush to 55amps. With or without the soft start the compressor had a notable vibration. My EU7000 is just to small to start the Compressor Effectively.

In my case frequency stays perfect but voltage drops below the 200 and the compressor never gets up to speed and vibrates like crazy.

When I parallel my eu7000 with my eu2200 the AC unit starts effortlessly.... Not my idea of a win, but at least I have an ace up my sleeve.

In your case I don’t think THD is the problem. You need a good quality meter with a fast refresh rate like a fluke meter to check your voltage at startup. Videoing my meter allowed me to catch the frame showing my voltage dropping below the minimum voltage threshold on the compressors nameplate. 208v is the number on my old Copeland scroll.
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