HELP, new at the job

[jrgriffhusker]

I'm 11 weeks from graduation and just started a new job as a service technician. I have a 13 year old Lennox unit that is short cycling, where do I start looking? Any help is greatly appreciated

[BigJon3475]

Is the system over sized is where I'd first look.

[jrgriffhusker]

You know now that you said that I realize that I'm not going thru enough steps to find the answer. I couldn't tell you the size. My pressures were 225 hi/ 70 low side. r-22 refrigerant. It's pulling the right amount of Amps, the superheat was 33 degrees and the subcooling was 60 degrees, and I had 27 degrees temp dif on the condensor.

[BigJon3475]

You have other issues. Go back over your superheat and subcooling (charging) section of your schooling.

[kelvin-459]

I'm thinkning if the unit was oversized & 13 yrs. old, this would have been a persistant problem. Are you hitting the thermostat set-point? Is the compressor going out on thermal limit? lots of places to look.
Good luck

[BigJon3475]

Well lets do this. What is your definition of short cycling?

[jrgriffhusker]

I told my boss I suspected an overcharge, but my pressures aren't that bad. I think it might be an internal overload in the compressor. Because I really think I was off on my temps or something, first time by myself. I really feel foolish because I really had it in my head I'd figure it out right the first time. I don't want to be the scrub of my little town. I guess everyone needs to start somewhere

[jrgriffhusker]

Thst is not being satisfied, which is what kind of leads me to believe that it's an internal overload.

[Joe Cool]

I don't know what your ambient temperatures are, but those pressures sound about right but the superheat and subcooling readings are way off. Are you sure that you know the proper way to check superheat and subcooling?

[jrgriffhusker]

Short cycling means in this instant. Compressor runs for less than 10 minutes, and when it stops it takes about 5 minutes before it starts again.

[BigJon3475]

Ref. gas cools the compressor. Seems to me from your readings you have a restriction. It will take time to get things to the point where you wanted to start. I say go in with open eyes don't count yourself done before you even get to the job. Reading on here even the very seasoned techs get brain farts.


Starving evaporator and stacking refrigerant in the condenser.

[jrgriffhusker]

I've redone the readings in my head and I believe they are closer to 12 sup and about 27 sub. Just guessing though. Ambient temp is 87 F

[BigJon3475]

Can't guess in trouble shooting you need exact and specific information everytime. Either way you still have a high subcool. Look towards your metering device. Until you get your 15 post and become a pro this is about as far as any advice that I can give.

[jrgriffhusker]

When I first approached the Evap coil there had been ice present but it chipped off pretty easy like they turned the unit off after they changed the filter. I'm just guessing but I think they changed the filter when they noticed it got hotter and saw the ice on the line. I'm going back tomorrow afternoon. I also noticed that when it cut out, if I closed the contacts the comp sounded like it was struggling to get started again. Could the run cap be the problem or is that a part that's either good or bad? Thanks for the help

[wolfstrike]

i'm guessing the discharge line is hot as hell
(i don't know why i think that)

[Joe Cool]

When I first approached the Evap coil there had been ice present but it chipped off pretty easy like they turned the unit off after they changed the filter. I'm just guessing but I think they changed the filter when they noticed it got hotter and saw the ice on the line. I'm going back tomorrow afternoon. I also noticed that when it cut out, if I closed the contacts the comp sounded like it was struggling to get started again. Could the run cap be the problem or is that a part that's either good or bad? Thanks for the help


So are you saying when it cuts out that the contacts are not closed?

[kelvin-459]

I would question the ice on the evap before the run cap.
Could be a restriction or bad txv starving the coil and keeping the system from equalizing, couple that with a charge problem in the first place and things get really interesting. re-check you sc/sh check you metering device & go from there.

[jrgriffhusker]

Yes when the compressor stops the contacts open. I really don't think anything is wrong with it mechanically, just electrically. Only because I don't think I'm doing my steps correctly, I need to slow down. I'm going to start all over on my readings and pressures just to be sure. Oh yeah if I have the model and serial number can I get a trobleshooting guide to the LED lights because they were flashing two quick flashes non stop.

[badbillr]

It sounds like, from what you are stating, it is a low voltage control issue. I will elaborate- if the contactor is opening after 10 minutes and then closing again after 5 minutes, I suspect it could be the t-stat is being satisfied. When you go back, turn the t-stat all the way down when you're servicing the unit so it won't shut off while you are looking at it. If it turns off like it has being doing after you set the t-stat low, look for a safety switch that may be opening when it should not be. When it turns off, use your voltmeter and see if you have 24v between yellow and common at the terminal board or wire nut connections- do not check it at the contactor just yet. No voltage at wire connection, check the float switch or fire stat. Possibly malfunctioning t-stat. If there is voltage at wire connections, check for open low or high pressure switch by using your ohms/continuity meter. Tell us what you find, ok! good luck!:)

[Joe Cool]

If you were to turn the thermostat all the way down, would it continue to run or would it still short cycle?

[jrgriffhusker]

Thanks everyone, I'm headed to bed. I definetly have a whole bunch of ideas to go on now. I'll figure it out and let you all know what goes down.

[BigJon3475]

I don't know maybe it's just me but with 27ºF of subcooling the t-stat could possibly be doing this?

[Joe Cool]

I don't know maybe it's just me but with 27ºF of subcooling the t-stat could possibly be doing this?


Sounds like he wasn't able to keep it running long enough to get an accurate reading with the gauges.

[Shophound]

I've redone the readings in my head and I believe they are closer to 12 sup and about 27 sub. Just guessing though. Ambient temp is 87 F

You can't subcool below ambient temperature unless there is a restriction between where you took the reading and somewhere inside the condenser. If your ambient temperature is 87 degrees, and your head was 225, your saturated condensing temperature is around 110. 110-27 = 83. Either you have a restriction or you need to retake your subcooling readings and note carefully how it compares to your ambient temperature.

[BigJon3475]

Sounds like he wasn't able to keep it running long enough to get an accurate reading with the gauges.


I don't know much about anything but even after 5 minutes my subcooling isn't ever showing 27º unless I have a restriction.

[Joe Cool]

I don't know much about anything but even after 5 minutes my subcooling isn't ever showing 27º unless I have a restriction.


For some reason, and I don't know why, I would be willing to bet that his actual subcooling is not 27 degrees.

By the way, how did you get that little degree sign after the 27? My keypad doesn't have that.

[dizzyrat]

look at people in the house adjusting the t stat

[wolfstrike]

start > programs > assesories > system tools > Character Map

[BigJon3475]

For some reason, and I don't know why, I would be willing to bet that his actual subcooling is not 27 degrees.

By the way, how did you get that little degree sign after the 27? My keypad doesn't have that.


hold down alt and type 167 on the number pad on the right of the keyboard


or you can do as Wolfstrike said but you have to type more numbers that way. it's your choice though.