internal overload tripping

[griz]

I have an Applebees account. I just replaced condensing unit that serves three med temp R-22 boxes with each having its own stat,txv, and solenoid valve for their prep line. It is a pump down system. After I found vitals ok with the excepion of slightly elevated discharge line (160F to 189F) fluxuating with the condensor fan control. I walked away and the next day I found internal overload tripped, checked vitals and they seemed ok. Installed warrantee compressor thinking it was a bad overload. Three weeks have gone by with no problems but I found overload open again. Could I maybe have a one bad txv?

[skpkey9]

need more info ie. superheat readings , amp draws discharge line temp (hot gas), pressures, and what kind of refrigerant you are using.

[skpkey9]

sorry, just seen r-22 and discharge temp but still need more info.

[griz]

I have head cycling between 200-250 psig with 9 dg subcool with clear sight glass. Amp draw is under RLA. Suction starts if all 3 boxes calling 48 psig with 12dg superheat. Keep in mind this is a split system. Now as each box satisfies, (which they pull down in a hurry) suction drops and the superheat rises up to 45 dg. I have not yet checked each individual superheat at each box. I have only checked superheat at the compressor. This problem just started I have been doing maintenance in it for five years. The condensing unit was speced from existing unit and I know it has been matched up corectly.

[refertecbd]

Whats the LPC cut out setting? System might be going into vac. when all tstats are satisfied.

[markwolf]

did you replace the solenoid valves too?I have seen many a condenser short cycling on low pressure switch due to a slight blow by.a compressor starting & shuting off every ten mins or so will overheat.Take a five gallon bucket up on the roof,have a seat & watch it for awhile.

[skpkey9]

monitor your superheat at all the boxes and at the compressor , if the superheat conntinues to rise over 45* . you will overheat your compressor. also what they said about possible short cycling. and again what is CI and CO on LPC.

[griz]

factory CO setting of pressure switch was at 4psi and 30 CI . I raised it to 12 psi CO and 30 CI once I found OL tripped. That might be a good point about a solanoid valve leaking by. I have sat and watched this unit satisfy and start back up. But I did not know if stat acually satisfied or solanoid valve leaking by. I may have to take a second person to watch condensing unit while I check stats in boxes and also to take superheat measurements of each box. There is an off cycle defrost solanoid valve at condensing unit which was replaced but the three box solanoids have not.

[Airmechanical]

factory CO setting of pressure switch was at 4psi and 30 CI . I raised it to 12 psi CO and 30 CI once I found OL tripped. That might be a good point about a solanoid valve leaking by. I have sat and watched this unit satisfy and start back up. But I did not know if stat acually satisfied or solanoid valve leaking by. I may have to take a second person to watch condensing unit while I check stats in boxes and also to take superheat measurements of each box. There is an off cycle defrost solanoid valve at condensing unit which was replaced but the three box solanoids have not.

you dont need a second person to do those sort of tests!

turn the stats all the way down to full blast, then pull 1 wire from the solenoids, cycle them by connecting wire back up or,

turn all the stats up, and see if the pressue leaks by the solenoids, you will possibly see frosting on the outlet side of the solenoid/s that is leaking

what are the differentials on the stats set at?



.

[skpkey9]

You won't always get frosting from a leaky solenoid valve. you may get sweating depending on how much is leaking by. After valve has closed wait a couple min then find out what your temp difference is by thermometer or by hand. If valve is leaking then you should be able to feel it by hand or visually. hope this helps

[badbillr]

single or 3 phase system. this sounds like 1 of two possibly problems. sounds like a condenser fan motor issue, letting compressor get hot and shutting down on over-load. or if single phase, compressor start cap failing.

[simpleman]

or if single phase, compressor start cap failing.

This ones got my vote.

[skpkey9]

Sooooo.... what did you find ???

[ndfrozen]

I have an Applebees account. I just replaced condensing unit that serves three med temp R-22 boxes with each having its own stat,txv, and solenoid valve for their prep line. It is a pump down system. After I found vitals ok with the excepion of slightly elevated discharge line (160F to 189F) fluxuating with the condensor fan control. I walked away and the next day I found internal overload tripped, checked vitals and they seemed ok. Installed warrantee compressor thinking it was a bad overload. Three weeks have gone by with no problems but I found overload open again. Could I maybe have a one bad txv?

I don't known you're systems, but around here all the applebees had serious problems with condenser capacity issues, taking out compressors. What we finally did was put in a water cooled coil and that solved the overheating issues once and for all. hope this helps.:D

[miller-cold-filtered]

check your low control. it may not doing its job correctly. i have seen one tha would work and then would not work.

[fire]

I would try lowering the fan cycling settings. youmay not be getting enough gas cooling to the compressor if one evap is calling and the fan doesnt start untill 250 head pressure. try 25 ps1 lower for co,ci. super heat will be high when only one evap is calling. I dont know how you can over come this problem on a system with 3 or 2 evaps.

[Jabarco]

Have you confirmed that the liquid receiver tank is actually big enough to hold the entire refrigerant charge after all three boxes' liquid line solenoids have closed? The compressor may not be pumping down and cycling off....instead it may be tripping the compressor overload when you think it's pumped down.

Jabs

[Dowadudda]

That is a piss poor way to control a single condensing unit.

And very bad for the pump. I see a scenario, where, say two of the three loads are satisfied, and those 2 solenoids are closed, now you only have one calling.

Low suction. High Superheat. Cause the pump is now way oversized. High Superheat will cause high discharge temps. Maybe to the point where the compressor is not getting enough suction gas to cool the motor windings properly.

And if there is no time delay on there, it wery well possibly is short cycling, which is also a possible cause of overload trip. Anything from a contactor not making on all legs everytime to, lack of oil return, to no suction gas to cool motor.

Controlling a single compressor in this way is always sooner or later death.

This system can still work as is but you must install a hot gas bypass and desuperheating feed. This will falsely keep compressor loaded up and properly cooled when only 1 load or 2 loads are on.

I am surprized your seeing this at an Applebees. I have built 13 applebees, doing all the refrigeration, from the walk ins to the prep lines. I have never seen this specified here in my area. As a matter of fact, the ones I have done, the design guys are looking out and have put some real good control and some solid thinking into how it's going to work and be serviced.

[griz]

Have some more information on unit. I have tested tev's they are working properly. With warm boxes and condensing unit is started up, suction is good at 68 with 7dg superheat at compressor. Head is condensing 30dg over outdoor ambient (it was hot so cond fan on continuous). As boxes start satisfying suction starts falling and superheat climbs along with discharge line. With just one box calling suction at 25psig with the suction line temp at compressor 70dg-84dg. Since saturated temp at 0dg with 25psig there is 70dg-84dg superheat. Discharge line temp topped out at 205dg. I looked at line set and found liquid and suction lines taped together and insulated together. Line set is 39ft long. I seperated lines under boxes and insulated suction line seperatly. When boxes are calling I measured 25dg-40dg suction line out of each box which means suction line is increasing over 40dg by the time it makes it to the compresor. In regards to the line set together maybe they are trying to keep liquid subcooled and not care about superheat. We have two other Applebees in the area with the same readings with no problem with ol tripping. Although we have deffinate capacity problems when oudoor is over 95dg. I also have bad door gaskets on doors I am wondering if this could be part of problem as well.

[Dowadudda]

I am confused.

How do you have 7 degrees superheat at compressor, a remote air cooled condensing unit, and then have 40 degree suction temperature gain from evaporator coils to condensing unit. These two occurences could not exist in the same system simoltaneously. Your all over the map with explaining this.

[Dowadudda]

if you read my first reply and truly get what I am trying to say so you can think a bit, it's really pretty obvious how you can have high superheat, low suction volume ( cool suction gas for cooling windings of a motor) High dishcharge temps, (bad for oil) in the way you have described this systems control and application set up.

[griz]

dowdudda, I don't know why you are confused. I said there is 7dg superheat when all three boxes are calling when the boxes were warm. vitals are fine durring a warm box start up. example: after time off defrost, after ol resetting, or if you manually shut system down. Then as boxes start satisfying vitals fall in the crapper. That is the problem sir and that was my question. Why is there such an increase in superheat. I do understand refrigeration therory although I am not a master. I realize that when only one box is calling there are not enough gas to cool. I assume part may be from the line set issue. Since I found out another store has the same operating vitals maybe this is the way this system works. Maybe I have a non refrigeration issue. Sorry you are not following me. I can tell from your negative remarks about the design, but keep in mind this store is ten years old with three other stores in the area controlled the exact same way. This is a new issue. We were not the installing contractor, You may not like the design "but it is what it is" .......If you have a phone number to Applebees "design guys" could you pass it on to me because a have some Questions for them.

[Dowadudda]

7 degrees of superheat is not fine at all. Dangerously close to flooding that pump with all 3 on. Copeland wants to see min of 20 degrees max of 45 degrees.

The increase in superheat with only one coil active is because you have an oversized system when only one system is calling, pulling suction so low sucking off the one coil it takes your superheat measurment and jacks it up. High Superheat, causes high discharge temps. High Discharge temps (not high pressure) and the lack of suction volume cool gas is my best guess to explain why your getting overload trip. Maybe a start components thing as others have mentioned. I dunno.

If it were me, I'd go visit one of my other stores and find out what the difference in control is. Something is up.

I wish I could be more help, I apologize for the negativity. I still think it's controlled stupid. Single units with multiple loads is disastrous if appropiate measures are not taken such as hot gas bypass and desuperheating.

[Dowadudda]

if it were me. I'd set the low pressure control to cut out at my minnimum desired temp of any one of the boxes. I'd timedelay the pump 1 minute to 2 minutes. This might help keep all 3 coils more active. and less of this lack of load.

Still. I can;t help myself from saying. This is the wrong way to control a single unit with multiple loads.

[markettech]

I have an Applebees account. I just replaced condensing unit that serves three med temp R-22 boxes with each having its own stat,txv, and solenoid valve for their prep line. It is a pump down system. After I found vitals ok with the excepion of slightly elevated discharge line (160F to 189F) fluxuating with the condensor fan control. I walked away and the next day I found internal overload tripped, checked vitals and they seemed ok. Installed warrantee compressor thinking it was a bad overload. Three weeks have gone by with no problems but I found overload open again. Could I maybe have a one bad txv?

Internal overload.........just curious, what horsepower compressor?

Outdoor or indoor condensing unit?

[griz]

18,ooo btu,s and split condensor on roof