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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Leibert 2ton ceiling mount AC will not stay on. Runs

Customer Question

Leibert 2ton ceiling mount AC will not stay on. Runs for 15 to 30 minutes, then will not come back on unless you set the control to "off" overnight.
Its not the condensation pump, I checked by filling with water.
Model mme024e-xc1.
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
Update: when you turn it on, the compressor runs but the evaporator (inside) fan does not run. After a few minutes of the fan not running the compressor turns off.
Customer: replied 1 year ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Phil replied 1 year ago.
Tell me please if this is a computer room cooling system or not, and about how old it is. and if the air filter has been changed regularly or not. We can go from there with a phone call later if it turns out we need it. .
Customer: replied 1 year ago.
Yes it a computer room ac. Made in 1998, new compressor unit in 2014. Filter could use replacing soon, but coil is squeaky clean. I turned it on a few hours ago and it ran normally for about 30 minutes, then shut down.
Customer: replied 1 year ago.
Here are some pics
Expert:  Phil replied 1 year ago.
Thanks for the pictures.There is most likely something going on at the compressor unit that was installed in 2014, it may have a refrigerant leak and by cycling off on is low pressure cut out switch. Tell me a lot about your technical skills and what instruments you have if any, I can coach you from there most effectively. Or if you can tell me which direction you are from the center of the nearest city I can locate a good service outfit or two for you. .
Customer: replied 1 year ago.
I have observed the compressor running with the evaporator blower not running. In this case wouldnt we expect the compressor to turn off after a few minutes? Fan spins easily by hand. Wouldnt that point to a relay/control issue at the evap?Electrical engineering and 20 years in the it industry. Multimeter is only instrument I have available.
Customer: replied 1 year ago.
It never cycles back on. If I leave it off for hours it will come on one time for 30 minutes, blow cold air, then evap blower (and possibly compressor) turns off without ever reaching lowpoin of 74 degrees. I cant say for sure because the compressor takes 3 mimutes to get to so I cant observe evap fan and compressor simultaneously.
Expert:  Phil replied 1 year ago.
Hello again,
Indeed, if the compressor runs, but the evaporator blower is not running, it would be a bad relay control at the evaporator, assuming the evaporator blower runs freely at other times and it is a PSC type motor (PSC =permanent start capacitor)
Liebert is sophisticated equipment, in 1998 they may have been early adapters and installed a variable frequency drive type blower motor in order to control humidity more precisely... the type they would have used is called an ECM motor, now common, it has permanent magnets in the rotor and is wound for 3 phase DC, its end bell uses capacitors and and a varistor to receive a 0-10vdc signal and pulse power to the windings according to the speed called for by the 0-10vdc signal.
The varistors tend to go bad and are easy to replace,
You can identify it by its extended end bell, with 8 to 12 wires attached and no run capacitor.
Look that over, let me know what you find, we can go from there.
Customer: replied 1 year ago.
Sounds similar to pulse width modulation. The end bell looked somewhat large an is unvented; but it appeared to have 4 wires. I will send schematic from side...
Expert:  Phil replied 1 year ago.
If you can send a diagram from inside the liebert air handler that will be useful as well. .
Customer: replied 1 year ago.
Sorry its not a better pic, it is legible when I zoom in...
Customer: replied 1 year ago.
And this unit appears to not have humidifier or reheat options.
Expert:  Phil replied 1 year ago.
Thanks, ***** ***** old style 2 speed blower motor, not an ECM or variable speed of any type, so that if its not running we need to look at: http://screencast.com/t/cWpnqSvigmP
Customer: replied 1 year ago.
The unit is 30 miles from my house, so i will perform indicated measurements tomorrow by 1pm eastern time and post findings.
Expert:  Phil replied 1 year ago.
That will work, I am in all day.
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