Amana RCE36C2C condensor fan runs slowly with AC off

[Lifespeed]

I have a 12 year old 14 SEER Amana RCE36C2C condensor mated to a Amana AMS95 17" wide air handler. It has been a good setup, after correcting some installation flaws I won't get into here.

Recently I noticed the condensor fan was running full time, although not at full speed. I cycled the AC at the thermostat, and the fan correctly shut off at the end of the cycle. I should note I saw a flash of light when the relay engaged under command from the 24V thermostat. A couple days later I went out there (it is heating season now, AC hasn't been turned on) and the fan was running slowly again. So I pulled the fuse disconnect in the wall-mounted junction box to shut it off.

I looked at the schematic and it seems pretty straightforward. As far as I can tell there is no path to power either the fan or compressor except through that relay. I'm thinking the relay is bad, but this seems a strange behavior - the fan being powered at a low setting. Maybe 1 leg of 220V? As an aside, the start-run capacitor was replaced a few months ago, although I don't think the fan running slowly issue started at the same time. After doing some reading online I realize it may be only one leg of the 220V is switched, so a winding short to ground could allow some power through the motor. I'll ohm out the motor to check this weekend. I think the bearings are getting worn anyway as I hear some rattling. I would like to make sure to replace the correct part, however, the bearings aren't bad enough to justify replacement by themselves I don't think.

Has anybody seen this symptom before?

 

[user 4883]

Yes, only one leg is switched and the fan will not run with just one leg.
The coil on the relay is responsible for pulling in the second leg to make it run.
The coil is part of the relay but, the entire assembly isn't that expensive.
Should be able to replace the relay to fix the problem. If this does not fix the problem then the problem lies within you control board or thermostat. These are the two items that tells the coil to the relay to energize and pull in the second leg of power to the fan motor.

 

[EdInKentucky]

you wrote ...

After doing some reading online I realize it may be only one leg of the 220V is switched, so a winding short to ground could allow some power through the motor.

In my experience, this is what you have going on. Not always true, but I've seen it a lot.
To confirm it, a resistance reading to ground, applying a fairly high voltage, will let you know.
Any motor lead to ground, should work.

 

[Lifespeed]

In my experience, this is what you have going on. Not always true, but I've seen it a lot.
To confirm it, a resistance reading to ground, applying a fairly high voltage, will let you know.
Any motor lead to ground, should work.

Good point, I was just going to apply my regular old Fluke multimeter to check the motor windings for a short to ground. But the problem is slightly intermittent, although it happens often enough. It does seem likely that only a high-voltage meter would be adequate to confirm a motor winding short.

 

[EdInKentucky]

yes, in my work there were many times that the hipot (for high potential, which means voltage) meter would pick up a winding short to ground, that the Fluke multimeter could not.
I think the winding shorts like that, are mainly due to weaknesses in the insulation on the windings.
The weaknesses are most often caused by multiple powerline surges, or nearby lightning strikes that are strong enough to weaken the motor, but not destroy it.
A good quality powerline surge protector helps a lot to prevent all this.

 

[Lifespeed]

As I don't have a megohm meter, I hired a local HVAC guy with a tester to come out and check it. He did not find a condenser fan motor short either. However, he did hear a faint 60-cycle hum, and discovered the compressor connector, which is held on by friction only, was somewhat loose. The outdoor unit had been running and cooling under thermostat control even with the loose connector. Seating the connector got rid of the hum, and the fan has not run un-commanded since. I looked at the schematic for the unit, which is fairly simple, but it wasn't immediately obvious how a loose connector could cause this issue.

 

[WyrTwister]

Just a guess , but maybe 240 VAV was back feeding through the compressor to the fan motor ?

God bless
Wyr

 

[EdInKentucky]

I have to admit, it's a mystery to me.
What you've described is a situation I've not seen before.

 

[pjones]

Is it possible the unit was actually calling for cooling or heating while the fan was running and the problem actually being with the compressor not consistently energizing because of the loose plug?

 

[Lifespeed]

Is it possible the unit was actually calling for cooling or heating while the fan was running and the problem actually being with the compressor not consistently energizing because of the loose plug?

No, the compressor always ran when commanded and the A/C was switched off at the thermostat while the condenser fan ran at a much slower speed than normal operation.

 

[WyrTwister]

OK , the traditional cool only condenser unit has 24 VAC from the furnace terminated at the coil of the contactor . That contactor switches on everything in the condenser , at one time .

Most residential units are feed 240 VAC single phase ( 2 hots and an earth ground ) . Residential units often use 1 pole contactors ( occasionally , a 2 pole ) . Were it mine , that is where I would look . If in doubt . replace it , they are not pricey . Does not have to be the exact part . A similar contactor of the same amperage or greater will be fine .

Be safe , turn the power off !

Merry Christmas

God bless
Wyr