A/C condenser fan intermittent

[soob]

Hey guys--

I was hoping somebody here might lend me a little experience before I call a pro. I'm kind of broke at the moment.

I have two A/C units and one seems to be having some issues. The condenser (compressor?) makes a fairly loud hum, louder than the other one at least. The fan doesn't come on when it first starts; instead, it'll run for a short time (20 seconds or so) intermittently. It seems to start okay and the fan motor doesn't make any unusual noises. The bearings are smooth. I am hoping the issue is electrical since both the compressor and the fan seem to be having problems.

The (dual run) capacitor looked fine, but the replacement was $12, cheaper than the tool to test the old one, so I changed that already and got no improvement.

I did notice that the relay (whatever it's actually called--the switch that the thermostat activates) makes a humming noise itself and though it seems to work, today when I went to look at it, it neither hummed nor made contact after I turned on the inside A/C, so I pushed it in with a screwdriver. It stayed in. No change in operation. Tapping the contactor with a screwdriver didn't seem to do anything either.

Should I replace that relay next, or am I off base? Anything else I can check or try myself before calling in the professionals? I do appreciate any help you can offer. New house, no money, you know how it is.

 

[soob]

It's a single pole contactor, so it being the problem wouldn't make any sense. Would it?

The fan runs once every minute or so, for seven seconds each time.

Why would it do this?

 

[pattenp]

What brand and model A/C is it and how old?

 

[soob]

It's a Westinghouse, only about 8 years old.

I just moved into this house and turned the A/C on, noticed the fan wasn't running and kind of freaked out.

I was looking at the way the thing is wired and got a little brave with my multimeter probes (I have a sort of functional knowledge of some electrical stuff but no real idea how to apply it to new situations) and I noticed that the fan motor gets 350v when it's on and nothing when it's not running.

The common to it seems to be tied to some kind of switch attached to a small refrigerant line coming out of the condensor before the dryer (?). I guess. I don't know much about these things.

Is that a pressure switch or a thermostat that controls the fan?

The other one (which is a Westinghouse about a year newer and a ton bigger) doesn't have that switch.

 

[soob]

This is it:

 

[pattenp]

I assume when you say it's an A/C unit that it's not a Heat Pump that you switched to A/C from heating and that it is a standalone A/C unit.

 

[soob]

Okay, so I'm starting to put this together. Here's my working theory:

1) The compressor is just kind of loud;

2) The contactor works fine; the thermostat must have some kind of delay

3) there is some kind of pressure or temperature switch on the fan for reasons unknown. I bet it would keep the fan on all the time if it was hot outside.

So I guess there's nothing to worry about other than the relatively noisy compressor?

 

[soob]

I assume when you say it's an A/C unit that it's not a Heat Pump that you switched to A/C from heating and that it is a standalone A/C unit.

Pretty sure it's not a heat pump. I live in the deep south and my house is heated by gigantic heater cores attached to the water heaters.

 

[brewchief]

Looks like it has a head pressure control so it can run in low temps.

The operation you are describing is normal if the temps are cool outside, as it gets warmer it should run longer until it runs all the time the compressor is running.

 

[pipsters]

Check the defrost sensor as well, being a heat pump is should have one. Mine went bad and caused my unit to run intermittently as well.

http://www.youtube.com/watch?NR=1&v=u5crdrc8jPE&feature=endscreen

I'd start with the obvious. I'm not a tech but I would think that a pressure sensor wouldn't turn off just the fan (that is what is happening, correct?).

If not that start looking at the defrost board maybe.

If not a heat pump I'm not so sure...good luck.

 

[pipsters]

Also post outside air temp when this was occurring, as well as what settings you have on your tstat - do you have heat and cool? That will tell you if you have a heat pump or not.

 

[soob]

Yeah, the ambient temperature outside is about 65.

This A/C is for the second floor of the house, which is the one that's going to get used in weather like this [in the evening on days like this it's significantly warmer inside than out]. So I guess it sort of makes sense that only one of the two units has the fan controlled like this.

Honestly though I can't remember ever seeing the condenser fan have its own thermostat. But there are lots of explanations for that between me being dull and inexperienced.

Anyway thanks again everybody. I will eventually have the A/C looked at to see if there's a reason the compressor seems to be kind of loud.

 

[soob]

Oh, and before anyone calls me out for it:

1) I noticed the fan wasn't spinning during the afternoon when it was somewhat warmer outside;

2) I can't just open a window because of allergies; and

3) I wanted to fix the A/C before it gets 90 degrees, which could be any day now.

 

[philjafo]

Looks like it has a head pressure control so it can run in low temps.

The operation you are describing is normal if the temps are cool outside, as it gets warmer it should run longer until it runs all the time the compressor is running.

^^^^this^^^^ sounds like normal operation. Still not a bad idea to have it looked at every year.

 

[brewchief]

Yeah, the ambient temperature outside is about 65.

This A/C is for the second floor of the house, which is the one that's going to get used in weather like this [in the evening on days like this it's significantly warmer inside than out]. So I guess it sort of makes sense that only one of the two units has the fan controlled like this.

Honestly though I can't remember ever seeing the condenser fan have its own thermostat. But there are lots of explanations for that between me being dull and inexperienced.

Anyway thanks again everybody. I will eventually have the A/C looked at to see if there's a reason the compressor seems to be kind of loud.

Every A/C I've seen with head pressure controls has had a compressor that seemed loud, without the fan running you can hear it better and the pressures it's operating at are more like what it would be at on a hot day with more load on it..

Spring cleaning/tune up is a good idea, more so on a unit that you have no history on.

 

[brewchief]

Oh, and before anyone calls me out for it:

1) I noticed the fan wasn't spinning during the afternoon when it was somewhat warmer outside;

2) I can't just open a window because of allergies; and

3) I wanted to fix the A/C before it gets 90 degrees, which could be any day now.

We have a dentist office that has to run A/C in single digit outside temps, the condenser fans sometimes don't need to run all day.

I wish more of our customers would check operation of their A/C before the hottest day of the year, when they find out it doesn't work and it's 100 degrees out they don't understand why we can't get there in the next 20 minutes.