ReplyWhats a couple compressors? Is this 2 systems or one 2stage system?
Regular Guest
Hey guys, what's up. I hope everyone is doing well. Ive been working as a hvac tech for the past year at a mushroom farm. I got my associates degree in science and completed my hvac-r training at a local tech school... I'm doing well at my job and can figure out most problems but sometimes I wish I had a mentor I could rely on when I'm absolutely confused. Thank you........ Right now I got a couple compressors going off on thermal overload...we cycle are fans to come on at 300 psig and my low side is currently around 40. I'm thinking I got a restricted tev. Any suggestions?
Regular Guest
Whats a couple compressors? Is this 2 systems or one 2stage system?
Regular Guest
One 2 stage system
Professional Member*
Compressors cycling on overload is not good. Model # & amperage are needed, along with refrigerant, pressures & temperatures. Along with other things.
Regular Guest
I agree.
Regular Guest
R22. Fan cycles on 300 psig. Superheat is 14. Low side psig is 40... Room is 55 degrees. I weighed in the correct charge according to the nameplate. Condenser coils are clean. Fans working. Filter drier not restricted.
Regular Guest
Thermal Overload or The compressors are getting too hot is bad.
Why do you cycle the fans at 300#? Im guessing the ref. is R-22?
300psig fan cycle is high in my opinion.
Regular Guest
I felt this was high also but it's a standard my "coworkers" go by... They where here before me and that's where they put it.Originally Posted by drpsr99
Regular Guest
The space your cooling is 55F??
Regular Guest
Yes. The room is 55 and the thermostat is set for 52
Regular Guest
Is the liquid line long? What is the size of it ie.1/2 ect.? Is it the correct size for the lenghth of run and unit ton? How do you know the coils are clean- Have you split the outside ones? Have you verified the air filter and INNER evap. is clean? No restrictions on blower blades or caught in wheel? Is the AHU belt drive or direct? How many amps does it draw to name plate amps? After you verify all of that, you may just need a hot gas bypass kit for better capacity control then 300# fan cycle
especially when your cooling to that low of a temp 52F. But again I would certainly verify all above before the HGB recommendation.
SDC/Educational/Membership Committee*
Give us the model of the condensing units as well. I have a suspicion that you may have some refrigeration condensing units which are misapplied.
...like medium temp units for a high temp job.
Regular Guest
Thanks for the reply.. I can tell I like this community already. Yes the size of the pipes are correct. I based that on the fact that we have over 150 units all sized the same way.. as of right now all units are working up to capacity except for this particular unit. The blower is belt driven and I'm getting correct rpm and proper amps....... A couple days ago the pipe coming out from tev was 28 degree and another tech adjusted the tev for it to be 40, now it's overheating... I think he created a restriction?
Regular Guest
Sorry, can you elaborate?Give us the model of the condensing units as well. I have a suspicion that you may have some refrigeration condensing units which are misapplied.
...like medium temp units for a high temp job.
SDC/Educational/Membership Committee*
Without the details of what it is you have there I can only speculate but to maintain 52°F your system should be running a lot higher than 40 psig suction...or 17°F SST. The suspicion I have is you have condensing unit designed for a medium temperature application (and they have been purposely holding the suction down to keep them running.) These units will run very high discharge pressures and overload if run much above about 25°F SST. The "normally" high discharge pressures and the other tech's throttling down the TXV are telltale signs.
I doubt you have regular A/C units because they are intended to run high suction pressures and still maintain reasonable discharge pressures. If you were to run an A/C unit at 40 psig, there's no way it would run at 300 psig unless the condenser were badly plugged up.
Regular Guest
Thank you. Yes everyone is always saying that we are asking these units to do something that they were not designed to do lol.. even the owner of the company saids this frequently
Regular Guest
You said you had over hundred of these same units. What does the pressures run on one that is running correctly. The medium temp condensers ought to be all right running at 55. As long as you have a liquid reciever installed on the high side. You should be able to set the txv to 10 super heat right at the end of the evaporator. I too feel that 300 is to high, but it should not cause compressor overload or system malfunction set at 300. Because that is only simulating a little over a hundred degree day.
Regular Guest
Yes. Most units are running at 50-55 low side.we have a accumulator on the lowside that is supposed to prevent liquid coming to compressor. Two stage 10 ton whetherking.
Professional Member
Sounds like you are working on high temp refrigeration here and not AC. I'll assume the exp valves are set up with the right orifices for this application. For my refrigeration on medium and low temp I usually set my txv 20F below box temp. Not sure if that is 100% correct as I'm self taught on refrigeration. If someone played around with the txv and suddenly the issue starts it's a good indication that is what the problem is. Also 300# is definitely to high for r-22. A regular ac condenser can actually be converted over to work in a refrigeration setting. I don't know why you would do it but I have seen it done. The old guy who did it was crazy genius though.
Regular Guest
Yes a lot of people are dong that now, because its cheaper than a skid. But you need to add the liquid receiver, low and head pressure control. I agree I think his problem is txv.
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