I have just discovered that the Copeland single phase scroll type compressor installed in many AC brands have a tendancy to run backwards if power is interruped. I personally have caught a Trane, Carrier, Heil, and a Goodman unit compressor running backwards. I discovered it on a weekend service call. A Heil Heat pump package that we installed almost a year ago unit was not cooling after a slight power interruption. Upon arrival, discovered the compressor was off line due to winding temp. Checked all electrical connections and capacitor tolerances. After cooling down the compressor with a garden hose, was able to start the unit. Checked unit for proper opertion and refrigerant charge at that time and could not find any problems. Monday morning I called the Heil rep and asked the tech support fellow. He was perplexed until I informed him of the slight power loss. At that time, he informed me of the possibility of the compressor running backwards if the power is jocked off and on. Anyone experienced this issue?
BlueShark
Common problem on older scrolls. Right along with the check valve sticking in the discharge of compressor. Acutually responded to call that the customer said the unit would scream when it shut off. The compressor would spin bacwards fast enough that the condesor fan would start turning. The solution for the running backwards after power surges is a time delay. Best solution for check valve sticking is a magna check valve. Make sure it can stand the discharge temps. since it has to go in the discharge line.:.02:
In most cases, the batteries are there to keep the clock running. The cap is a filter, not really there to 'keep the memory'. The settings are usually stored in NVRAM, and as such, don't go away when the power is lost. The clock is the only real concern on power outages.
And yes, most digital stats should have a common wire...
And yes, most digital stats should have a common wire...
The compressor won't pump. The pressures are pretty much the same on both sides & it usually sounds funny too.
It's called transient torque.
When a power interruption causes a radical change in the phase angle the magnetics can spin the rotor the other way.
I've seen it happen on 3 phase motors in YORK centrifugal chillers the impeller actually unscrews and falls off.
And a Nest t-stat will power itself by tapping the cooling contactor if there's no ground wire (plays hell with an electronic damper control though).
When a power interruption causes a radical change in the phase angle the magnetics can spin the rotor the other way.
I've seen it happen on 3 phase motors in YORK centrifugal chillers the impeller actually unscrews and falls off.
And a Nest t-stat will power itself by tapping the cooling contactor if there's no ground wire (plays hell with an electronic damper control though).
I've been noticing this as well. The Ruud tech I called out on site for a brand new package unit showed me that a split momentary "glitch" in power can make them run backwards. From what I was told Copeland actually removed a safety in their compressors that prevented this thinking the overload would catch it. Well it doesn't. Most of the models I have found this on were the 2012 models. I'm not sure if they have fixed it yet but I have been installing delay on break relays on the contactors as the momentary bump in power won't trigger the board time delay or the tstat delay but will trigger the separate relay I install.
If this is happening on Heat Pumps there's a possibility that it is the reversing valve sticking instead of the compressor running backwards. The symptoms are similar and there can be a grinding type sound though the noise is usually not as loud. Before they started using the quiet shift defrost boards it was a common problem. Even with the quiet shift boards they usually have a jumper that can disable the quiet shift.
I have 4 out of 5 Bosch geo units doing this on transfer back to utility power
I have a large house with five Bosch geothermal units. One water to water, one split and three combo units. In January we had three power outages. Thanks DTE! No issues transferring to the generator (60Kw). Issue happens only when we transfer back to utility power. During the last power outage 4 out 5 of the units tripped out on thermal overload. Subsequent investigation and duplication of the issue revealed that the scroll compressors were in fact running backwards after transfer back to utility power!
The UPM (Unit Protection Module) is worthless and does not detect or protect the unit when this happens. The compressors run backwards until they trip out on a thermal overload. The units are blissfully unaware that this has happened and as a result the fan continues to run, etc. The water to water system takes forever to cool down and recover. The split and the combo units recover faster.
I am guessing that everyone that has this issue is being told the same thing. You are unique, we never see this and we don't know what is going on.
The truth is that it is rare, but not unique and can happen on any unit.
Seems they would rather replace compressors under warranty than address the root cause of a potential failure.
I have found a product (SureStart) that will detect this condition and shut the compressor down. I intend to get five of these and get them installed ASAP!
More to come...
I have a large house with five Bosch geothermal units. One water to water, one split and three combo units. In January we had three power outages. Thanks DTE! No issues transferring to the generator (60Kw). Issue happens only when we transfer back to utility power. During the last power outage 4 out 5 of the units tripped out on thermal overload. Subsequent investigation and duplication of the issue revealed that the scroll compressors were in fact running backwards after transfer back to utility power!
The UPM (Unit Protection Module) is worthless and does not detect or protect the unit when this happens. The compressors run backwards until they trip out on a thermal overload. The units are blissfully unaware that this has happened and as a result the fan continues to run, etc. The water to water system takes forever to cool down and recover. The split and the combo units recover faster.
I am guessing that everyone that has this issue is being told the same thing. You are unique, we never see this and we don't know what is going on.
The truth is that it is rare, but not unique and can happen on any unit.
Seems they would rather replace compressors under warranty than address the root cause of a potential failure.
I have found a product (SureStart) that will detect this condition and shut the compressor down. I intend to get five of these and get them installed ASAP!
More to come...
So what you want is a unit built outside of design conditions! The utility is required to supply clean power within 10% of ratings. When they don't how is this the manufactures problem. Yes there are a lot of compressors and electronics replaced because of dirty power and believe me "YOU" do pay for it one way or another
You've found the solution a power monitor, not sold with residential equipment. Unless you want to pay more of course.
You've found the solution a power monitor, not sold with residential equipment. Unless you want to pay more of course.
Even roof top dual condenser fan units had FAN MOTOR reversals, but NOT by any UT'y glitch:
A slower-starting fan , in gusty N-OH nw-winds coming in, would have both fans turning backwards at a starting time.
ONE was driven continuously in reverse...
A/C service calling us out...
had to see it twice before appeasing the 'hotter' heads that been.
Replaced with new fan motor, end of problems...
What is confusing a bit, is the slower-starting motor was the dragger that stopped sooner in proper rotation , run off at a stop, ( that one that would STAY in reverse rotation).
Either way, I had to show it to the building supv, catching it in reverse.
The'president' of a very large, and very field experienced mechanical, in part of the equipment maintenance with me, said "THAT CAN NOT HAPPEN."
40 years in the field: his 'first' again.
A slower-starting fan , in gusty N-OH nw-winds coming in, would have both fans turning backwards at a starting time.
ONE was driven continuously in reverse...
A/C service calling us out...
had to see it twice before appeasing the 'hotter' heads that been.
Replaced with new fan motor, end of problems...
What is confusing a bit, is the slower-starting motor was the dragger that stopped sooner in proper rotation , run off at a stop, ( that one that would STAY in reverse rotation).
Either way, I had to show it to the building supv, catching it in reverse.
The'president' of a very large, and very field experienced mechanical, in part of the equipment maintenance with me, said "THAT CAN NOT HAPPEN."
40 years in the field: his 'first' again.
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