High suction, low discharge

[michigan1]

So I just installed a complete Rheem 5 ton, 14ajm series system ast november. HO tells me its not cooling as good. I arrive to find a loud compressor, 200 psi suction and 275 head. First thing that comes to mind is bad valves. A few minutes later the compressor cuts off on internal overload. I take a hose and cool it off. 10 min later, compressor kicks back on and pressures now seem normal (130/325) 13 subcool , 19 delta t. So I let it run for 20 minutes and take off. An hour later , HO called back and outdoor unit has stoppes running again. Bad txv?

[Six]

Why would you leave with a compressor running 225/200 without resolving the issue ?

Of course its going to trip again.

[lolson]

Overfeed. possible loose bulb or poorly insulated, over sized.
Suction pressure high, head pressure low, superheat low, subcooling low, amp low.
I don't see any superheat or subcooling

[michigan1]

Why would you leave with a compressor running 225/200 without resolving the issue ?

Of course its going to trip again.

I was planning on going back to replace the txv. Just wanted some feedback

[GrumpyPawPaw]

Is the suction line very cold? If not I would suspect the internal releif valve in the compressor.

[GrumpyPawPaw]

My above question applies when the unit is malfunctioning. I'm assuming the condenser fan was running? Condenser fan shutting off, when your not there? Check fan amps and the cap.

[Six]

I was planning on going back to replace the txv. Just wanted some feedback

Ah...ok.

Well someone mentioned a week internal relief that sounds reasonable.

Even if your txv was wide open you wouldnt be equalizing like that.

It almost sounds like its a scroll running backwards.

[cboe]

bad valves or internal releaf open

[GrumpyPawPaw]

If bad valves, it wouldn't have returned to normal pressures.

[michigan1]

If bad valves, it wouldn't have returned to normal pressures.
Exactly

[michigan1]

Is the suction line very cold? If not I would suspect the internal releif valve in the compressor.

Ok this makes sense. IRV pops, compressor gets hot, then goes off on internal overload? Ive never had one do that but logical...

[SoFlaDave]

Sounds like a scroll running backwards to me as well. I was working on unit the other day and we had a little power brown out and the neighbors rheem unit started running backwards. I reset the breaker and it started up fine. Maybe they have a bad connection or floatswitch that is causing the unit to short cycle. Install a time delay and check your wiring inside and and out.

[michigan1]

Sounds like a scroll running backwards to me as well. I was working on unit the other day and we had a little power brown out and the neighbors rheem unit started running backwards. I reset the breaker and it started up fine. Maybe they have a bad connection or floatswitch that is causing the unit to short cycle. Install a time delay and check your wiring inside and and out.

Its single phase. You mean its running backwards on overload?

[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.:.02:

[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.

[t527ed]

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.


any safety or connection after the thermostat could still cause the contactor to chatter, i would still install a time delay at the contactor.:.02:

[MechAcc]

The new scrolls have a thermal relief valve. Once open it does the same thing as a pressure relief allows thermal overload to heat up and shutdown. The overload maybe resetting before the thermal relief closes. Showing no pumping action. Watering down the compressor reset both safeties. Make sure everything is clean. CFM is correct. And heard overcharging will cause the thermal to open as well.

[Mr Bill]

If bad valves, it wouldn't have returned to normal pressures.

Scrolls don't have any valves,at least not like the old recrips did. :grin2:

[MechAcc]

The Copeland Scrolls will have a decal stating that it has a thermal device.

[timebuilder]

The decal is applied to units that have a mechanism that disengages the scrolls from the motor, allowing it to run without moving the scrolls.

http://www.emersonclimate.com/en-us/Products/Compressors/Scroll_Compressors/copeland_scroll_commercial/Pages/advanced_scroll_temperature_protection.aspx

[mark beiser]

The decal is applied to units that have a mechanism that disengages the scrolls from the motor, allowing it to run without moving the scrolls.

http://www.emersonclimate.com/en-us/Products/Compressors/Scroll_Compressors/copeland_scroll_commercial/Pages/advanced_scroll_temperature_protection.aspx

The scroll mechanism still turns, the ASTP just bypasses the discharge gas internally, which is why no refrigerant is moving through the system when the ASTP is active.
The bypassed discharge gas trips the thermal overload in the motor windings.
http://www.emersonclimate.com/Documents/Products/Compressors/astp_overview.pdf

The compressors listed in the link you posted are commercial AC and refrigeration compressors.
The K5 scroll compressors used in residential equipment for the past couple of years have a similar feature. I works the same, but has slightly different implementation inside the compressor.
The previous K3 compressor don't have the ASTP feature.

I haven't noticed the ASTP warning sticker on a residential unit with a K5 scroll compressor yet.

[timebuilder]

The scroll mechanism still turns, the ASTP just bypasses the discharge gas internally, which is why no refrigerant is moving through the system when the ASTP is active.
The bypassed discharge gas trips the thermal overload in the motor windings.
http://www.emersonclimate.com/Documents/Products/Compressors/astp_overview.pdf

The compressors listed in the link you posted are commercial AC and refrigeration compressors.
The K5 scroll compressors used in residential equipment for the past couple of years have a similar feature. I works the same, but has slightly different implementation inside the compressor.
The previous K3 compressor don't have the ASTP feature.

I haven't noticed the ASTP warning sticker on a residential unit with a K5 scroll compressor yet.


First I'd seen that internal closeup. Nice.

[beenthere]

Its single phase. You mean its running backwards on overload?

Single phase Scrolls can run backwards if their check valve leaks through, and they have a short power outage and then come right back on.

[Mr Bill]

Single phase Scrolls can run backwards if their check valve leaks through, and they have a short power outage and then come right back on.


Yes they will, if you have not personally witnessed this like I have, some might find it hard to believe. :grin2:

[skippedover]

Is it a heat pump? Not familiar with the model number but if it's a HP, that's a classic reversing valve problem. Little difference or none between high side and low side and a loud compressor!

[mcewans]

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.

I checked, and this works with the FocusPro Series. I am not sure about the VisionPro Series.

[jjmarquez84]

You should try and pump down the unit. If the unit doesn't pump down in seconds then its a bad valve.

[Trustco]

Can this happen if this unit short cycled , example customer playing w/ non digital stat?

[Redenius]

I agree sounds like it was running backwards. Will cause pressure to be equalized and overheat compressor causing it to trip.