Compressor "freewheeling"

[cashflow134]

I was wondering if anyone has ever seen this is after power was killed the compressor appeared to still run. This happened on a condemed compressor that would not pull box temp. When the compressor was "freewheeling" it seemed like it was at about half the rpm's it would be normally....i would just like some sort of explanation

[OregonYeti]

A valve problem allowing the high side to push through the compressor to the low side, running the compressor backwards???? Just a guess.

[cashflow134]

took the compressor apart i didn't see any valve damage not sure why the compressor was condemed it appeared fine although while pushing the piston up and down it seemed like there wasn't as much friction as there normally would be...

[mdharris68]

We had a one or two hp semi hermetic that would shake, rattle, and roll after the stat was satisfied. Freewheeling was what it was doing, but as close as we could figure it was a stator out of balance, according to the copeland rep.

[kevink1955]

If the contactor does not break both sides of the line (assuming single phase) and the compressor windings have an internal short to ground the compressor will still draw current and may continue to run.

Take a reading with an ohm meter from the 3 terminals to the compressor body. If you get a reading on any of them it's internaly grounded (shorted)

[the mojo]

took the compressor apart i didn't see any valve damage not sure why the compressor was condemed it appeared fine although while pushing the piston up and down it seemed like there wasn't as much friction as there normally would be...

Tear the whole thing down. Either a crank sheared off or two busted wrist pins.

[OregonYeti]

Ok a recip. Wasn't sure what type it was.

[juneair]

the connecting rod broke and the motor has no load. thats why it was just spinning to a stop.
The pistons separated from the motor.

[r422a]

Quote:
Originally Posted by cashflow134
took the compressor apart i didn't see any valve damage not sure why the compressor was condemed it appeared fine although while pushing the piston up and down it seemed like there wasn't as much friction as there normally would be...


There is definitely no load if the motor freely spins on shutdown. Since the poster states that the piston moves up and down when pushed by hand the pistons are still attached to the crankshaft- no broken wrist pins or rods. The crankshaft must be separated from the motor.

[refrigekid]

hi its cashflow this is my new user name...

anyway yeah there was no power at all it was checked with a meeter and also both the conecting rods were absolutely fine, has anyone atleast seen this?

[itsiceman]

[QUOTE]condemed compressor that would not pull box temp.

Sounds like it was inefficient. Sort of running but not full power? I have seen something like this. Mine was semi-hermetic 3 phase. It would spin and shake after pump down so we changed the valve plate and that took care of it (also found no oil trap in the suction line and added one). You might want the check the piping so you don't have to pay for a new compressor in a couple of weeks.

[OregonYeti]

How long does the compressor freewheel? Non-stop?

[refrigekid]

i want to say the comp was running (at a lower rpm) for about 2 min without any power to it

[jasond1011]

i saw one today . obviously its notRUNNING as there is no power. but it is doing something as you can here it make a noise. the high side pressure is bleeding back into the low side backwards through the compressor valves. this is not good cause if you feel the suction line right after shut off it will begin to warm up real fast as the hot gas discharge side begins to backflow. this can trip the internal heat overload if it gets bad enough but efficiency and performance is also lessened. I saw a 22 year old trane recip doing it last thursday. it will all be replaced this friday. It you listen close the noise diminishes after 4 to 6 minutes as pressures finally equalize. You gages will show a fast pressure equalization even on a non- equalizing txv and straight cool as the one i was on did.