Compressor gone bad

[Minitee]

Have a 7 year old Tecumseh compressor cooling my fridge/freezer.
Constant cycling AC unit. Hermetically sealed. 1/3 hp.

It worked "good" (ie, a bit noisy, but colder than a mother-in-law's kiss) until I accidentally left it off for a week. Now I can't get the darn thing to start.

I checked the capacitor and circuits. All okay; I installed a new capacitor just in case. The motor hums, but when it tries to start, it makes a grumbling sound, but doesn't kick in.

Is it time for a new one?
This wouldn't be caused by low refrigerant, would it? (I'm only asking because it's been a while since I checked it)

[ssullivan]

Originally Posted by Minitee

Have a 7 year old Tecumseh compressor cooling my fridge/freezer.
Constant cycling AC unit. Hermetically sealed. 1/3 hp.

It worked "good" (ie, a bit noisy, but colder than a mother-in-law's kiss) until I accidentally left it off for a week. Now I can't get the darn thing to start.

I checked the capacitor and circuits. All okay; I installed a new capacitor just in case. The motor hums, but when it tries to start, it makes a grumbling sound, but doesn't kick in.

Is it time for a new one?
This wouldn't be caused by low refrigerant, would it? (I'm only asking because it's been a while since I checked it)

Do you hear any loud "clicks" as the motor attempts to start? If so, could be one of the various safety shut-offs. You went through each of them testing for proper functioning?

Did you do a resistance test of the motor itself to see if the motor is shot?

Did you test to see if the motor is grounding out somewhere by testing resistance between motor and casing?

Are you sure the AC-DC rectifier unit is working properly?

Lastly, is there any reason to believe the supplied voltage to the compressor is too low?

[Minitee]

Thanks! I'll test the voltage.

Someone else suggested it might be a sensor tripping it off.

[GordMay]

Compressor failures revisited ~ By E.P. (Ed) Gravelle
Plumbing & HVAC Product News magazine
Goto Page 22:
http://plumbingandhvac.ca/online_mags/PHVAC-Aug07.pdf

“... Mechanical failure
Motor/compressor assemblies can fail mechanically, either through breakage of internal parts or compressor seizure.
Breakage of parts can be due to defects. However, the more common cause is from trying to pump liquids rather than gas.
Seizure usually results from the lack of lubrication due to lack of oil, or diluted oil (too much liquid refrigerant in the oil) causing cavitation within the oil pump that leads to oil pressure loss due to boiling refrigerant in the oil pump.
When compressors are idle, oil in the compressor can be seen if the compressor has an oil sight glass. Upon startup the oil level will drop quickly, causing the oil under refrigerant pressure to foam up violently. It foams up and passes through the compressor more rapidly at startup than during normal operation.
There is always some oil carried through the compressor while running. However, the greatest amount occurs on startup.
Oil foam-up and loss from the compressor oil is usually kept at a minimum, by:
...[/size]
Goto: http://plumbingandhvac.ca/online_mags/PHVAC-Aug07.pdf