High suction, low discharge

[SoFlaDave]

During a very brief power interruption (brown out) the expansion of gas in the compressor can start moving the rotor in reverse. If power is applied during that rotation it is possible for the motor to start running backwards until it overheats and it can do damage to the scroll. It can't pump so the motor isn't cooled by the suction vapor anymore. I had heard that Copeland fixed this issue at some point, but I still see it on equipement built in the last 5 years. For the record, I have only seen this happen to Copeland scrolls.

[timebuilder]

During a very brief power interruption (brown out) the expansion of gas in the compressor can start moving the rotor in reverse. If power is applied during that rotation it is possible for the motor to start running backwards until it overheats and it can do damage to the scroll. It can't pump so the motor isn't cooled by the suction vapor anymore. I had heard that Copeland fixed this issue at some point, but I still see it on equipement built in the last 5 years. For the record, I have only seen this happen to Copeland scrolls.

I'm with Dave.

I'd take the proactive step of installing a time delay.

For me, the "loud compressor" you mentioned right out of the box, along with the pressures, suggests to me it is getting started in the wrong direction. A time delay will help inhibit that effect.

[michigan1]

I'm with Dave.

I'd take the proactive step of installing a time delay.

For me, the "loud compressor" you mentioned right out of the box, along with the pressures, suggests to me it is getting started in the wrong direction. A time delay will help inhibit that effect.

Thougjt the visionpro stat had a time delay but it very well could be disabled. Thanks.

[timebuilder]

Thougjt the visionpro stat had a time delay but it very well could be disabled. Thanks.

It has it, and it is adjustable in installer setup.

BUT, it works based on when it (the stat) turns the compressor off ITSELF, or when it "wakes up" from a full power down.

If power is lost, the backup batteries don't let the stat know the compressor stopped, so it will come back on as soon as power is restored.

I think the time delay is a better choice than taking out the batteries, as most HO's would not like to have to reprogram the stat for time whenever the power goes off.

[Bmvbrfd]

I had one do that same exact thing tuesday. 11 year old Ruud 3 ton. Except it was running great, good pressures, subcool, superheat, delta T. It never shut off. Pressures went to about 200/275 compressor got REALLY hot. Was rated for 16.5 amps and was pulling 11.5 on one hot leg 3.5 on another. It had a leak in the evap coil and HO just wanted a whole new system

[Six]

What about installing a 5-2-1 on the unit ? Wouldn't it increase starting torque ?

Also a delay on make timer is cheap too if you want a no fail delay.

[t527ed]

older scrolls had a habit of starting up and running backwards due to a momentary loss of power. newer ones are not supposed to do that but it sounds like yours might be.
i would try putting a delay on break timer right before the contactor, only needs to be set for 15 seconds or so to prevent reverse running from happening.

something to try and much easier than a txv.

[Robert norton]

I had a Ruud 2 1/2 split system in a attic have same problem it was last year new install came out 2times with scroll running backwards hard to find what was causing problem it was the condensate overflow switch I wire at pan it would open for about 2 seconds then come right back on replaced the switch alls ok

[rlxdn10sity]

I usually wire the condensate safety switch to break R. 99% of the time I install a stat powered by equipment x-former. In the case of an erratic float it should cause the stat delay to come into the equation and prevent the compressor from restarting immediately. In the case of a more static obstruction in the condensate drain, it also makes for an obvious indication to the HO that there is a problem if the stat has no display.

[Cmstech]

Sounds like a restriction problem to me, like expansion valve or TXV is "metering" instead of flowing or even a liquid line solenoid valve bad

[mcewans]

It has it, and it is adjustable in installer setup.

BUT, it works based on when it (the stat) turns the compressor off ITSELF, or when it "wakes up" from a full power down.

If power is lost, the backup batteries don't let the stat know the compressor stopped, so it will come back on as soon as power is restored.

I think the time delay is a better choice than taking out the batteries, as most HO's would not like to have to reprogram the stat for time whenever the power goes off.

I think you can solve this problem by hooking up the C terminal to the common on the 24V. When power is lost, the compreesor is "locked out" and won't start up until the lockout delay in the thermostat is satified.

[Rob_in_WV]

Is this a HP? If so maybe check the defrost switch too. If it came from the factory with a switch stuck closed it would shut down the condenser motor, get it bypassing and when it comes out of defrost on time could be leading to what you are seeing.

[timebuilder]

I think you can solve this problem by hooking up the C terminal to the common on the 24V. When power is lost, the compreesor is "locked out" and won't start up until the lockout delay in the thermostat is satified.

That is not what I have seen in the field.

Of course, the least expensive installer bid for a commercial job means that a C wire is rarely provided, so in that situation, the point is moot.