A.C. help, contactor?, capacitor?, both?, other?

[Stand_watie]

This is an elderly (97) central unit rated for 4,200 BTU, manufactured by "Style Crest Products", Fremont Ohio.

Last weekend I noted it was blowing hot air, the compressor/fan was running and I thought maybe the problem was I had the window unit off and it just couldn't keep up (I have a double wide, and the central unit is only going to one side of the house, and in the heat of the summer I have to run a window unit on the other side of the house to keep up), I turned on the window unit, replaced the filters, cleaned grass/weeds from around the compressor/radiator and within an hour had 54 degree air blowing.

This weekend it was blowing hot air and the compressor/fan was not running. I figured I stirred up the fire ants and the got in the contactor. Took the access panel off and checked, had a few fire ants and a couple spiders, but not a lot, blew the area out with compressed air and pushed the contactor in, unit hums but fan doesn't come on. Checked voltage into and out of contactor - 240 in 240 out.  Took another access panel off (and in so doing joggled the wires around) to check the amps the compressor and fan are pulling, pushed the contactor in and the fan/compressor came on. Friend said the contactor is probably going out. My a.c guy said that might be it or it might be the capacitor going out.

The capacitor IS the thing that looks like a 70's era auto coil, right? It looks old/rusty but not visibly distorted or leaking oil. BOTH the contactor and the capicitor look like something I can easily replace myself IF I remember to prelabel the wires before disconnecting.

I have the name of a local parts warehouse that should have parts I need. What do the a.c. guru's on here think I should replace first WHEN it goes out again? Or do you have 12 more things it might be? How much should I expect to spend for a contactor/capicitor?

FWIW amp checks

Compressor
______________
red wire 20.5 amp
black wire 21 amp
(small)brown wire 5.4 amp

Fan
____________
red wire .8 amp
black wire 1.2 amp
brown wire .8 amp
(small) green wire .1 amp

[Ron]

Does the contactor pull in on a call for cooling? In other words does the contacter energize when the T-stat says "give me cooling".

If the contactor is pulling in but nothing runs then you need to confirm that both legs (assuming it is a two pole contactor) are making when the system call for cooling.

If the contactor is not pulling in, then the problem is in the control circuit. The control circuit most likely consists of: thermostat, control wiring, contactor and any safeties in the circuit consisting usually of only a high pressure switch and/or low pressure switch.

Do you have a multimeter in the house?

[never_retreat]

I tore my hair out the other day on something similar.

It was a 7.5 HP 3ph motor on an air compressor. Thing would just hum. (missing phase)
I had voltage on all 3 terminals in and out. 
Turned out that the contacts inside we almost burned off. Just enough to show juice but not enough to let the motor turn.

[Jim147]

This weekend it was blowing hot air and the compressor/fan was not running.

When it was just buzzing, was it the buzz of the contactor coil? Or was it more of a growl of the motor trying to start?

When your saying compressor/fan are you meaning both are not running? Or just the fan?

These type of problems can be a little hard. You have to catch it doing it and start checking without turning it off and back on, which can start it to working again.

You sound like you could figure it out pretty easy but I hate to tell anyone to get into an A/C unit in a public forum.   That whole liability thing.

jim

[280plus]

Yea, if you're getting neither fan nor comp it's either not pulling in on it's own or if it is one of the contacts is intermittent. There may be one or two sets of contacts (single pole / double pole) Is there one cap with three wires or two caps with two wires coming out of each? Fluke makes a nice $100 ish meter that includes a capacitor checker. I love the thing.

[280plus]

When it was just buzzing, was it the buzz of the contactor coil?

It's the BEES!! RUUUUNNNN!!!

 

I saw a rooftop unit once, up about a foot off the roof on an angle iron frame. The bees had built a nest underneath the unit from the bottom of the unit to the roof and about 4 FEET in diameter. You could hear it humming from like 15 ft away. So the owner says, "What do you do about that?"  I said, "I tell you to get an exterminator." 

[Stand_watie]

Yea, if you're getting neither fan nor comp it's either not pulling in on it's own or if it is one of the contacts is intermittent. There may be one or two sets of contacts (single pole / double pole) Is there one cap with three wires or two caps with two wires coming out of each? Fluke makes a nice $100 ish meter that includes a capacitor checker. I love the thing.

Two wires coming out of each.

[AJ Dual]

Capacitors are usually like $5 or so, so I'd replace it anyway.

http://www.grainger.com/Grainger/wwg/search.shtml?op=search&N=12913&Ne=10071&in_dim_search=1

[Stand_watie]

When it was just buzzing, was it the buzz of the contactor coil? Or was it more of a growl of the motor trying to start?

When your saying compressor/fan are you meaning both are not running? Or just the fan?

These type of problems can be a little hard. You have to catch it doing it and start checking without turning it off and back on, which can start it to working again.

You sound like you could figure it out pretty easy but I hate to tell anyone to get into an A/C unit in a public forum.   That whole liability thing.

jim

I wouldn't know the difference between the buzz of a contactor coil or the growl of a motor trying to start. My friend from work said the compressors sometime run smooth enough that I wouldn't be able to tell it was running by listening, the fan definitely WASN'T  running.

[Stand_watie]

Capacitors are usually like $5 or so, so I'd replace it anyway.

http://www.grainger.com/Grainger/wwg/search.shtml?op=search&N=12913&Ne=10071&in_dim_search=1

Will do. In THEORY what does the capacitor do? I understand the contactor is essentially a switch.

[Jim147]

If I was just putting one item in because I could never catch it when it failed, I would go with the contactor. I just haven't ran into to many intermittent capacitors.

I guess I'm feeling kind of lucky to have all the parts sitting here if I have something fail in mine.

jim

[AJ Dual]

Will do. In THEORY what does the capacitor do? I understand the contactor is essentially a switch.

It's like any other motor start capacitor, it provides a surge to kick over the cooling fan and compressor motors. Normal 110 or 240 AC (depending) is enough to keep the motor spinning and overcome it's load and internal friction etc. but not enough to get it turning over from a cold dead stop.

[280plus]

Think of it as det cord going off right at the moment you put power to the motor. 

[Nick1911]

It's like any other motor start capacitor, it provides a surge to kick over the cooling fan and compressor motors. Normal 110 or 240 AC (depending) is enough to keep the motor spinning and overcome it's load and internal friction etc. but not enough to get it turning over from a cold dead stop.

This is not to be confused with a run capacitor, which is also often found in hvac gear.  My understanding of a run cap is to create a fake phase that's out of sync far enough with the line phase so that the motor is more like a three phase.

I _think_ this is done to help give the motor rotational acceleration for a larger number of degrees per turn.

[Jim147]

What's more fun when it blows up?

An oil mess or confetti?

jim

[CNYCacher]

It's the BEES!! RUUUUNNNN!!!

"Not the Bees! Auuurghhgg!"

[280plus]

yes, in reality the capacitor in a run circuit causes the run and start windings to be out of phase. The farther out iof phase they are (up to 90*) the more start torque there is. With a start only the start winding recieves an out of phase jolt on start up and then the start winding/cap is dropped out of the circuit leaving the single mag field of the run winding to do the work. With a start/run set up the start winding receives an out of phase jolt through both but then the start cap drops out and the motor runs on run winding and start winding with the run cap in the start circuit creating two mag fields, one by the run winding and one by the start winding that are held out of phase from each other and create more run torque. The PSC (permanent split capacitor) motor has a run cap only in the start circuit which provide some extra torque for start and extra torque for run too.

So, to reiterate. a motor with no caps is called "split phase" and it will have both moderate run and start torque, a motor with just a start cap in the start circuit will have good start torque / moderate run torque. A motor with both start and run will have good start AND run torque. And a motor with just a run cap will have slightly better start torque than if it wasn't there and will have good run torque. 

[Stand_watie]

O.K. it ran until last night. Replaced both the contactor and the capacitor this a.m. It ran until this afternoon. Calling in a pro in the morning. I'm thinking a loose wire or connection between the contactor and thermostat.

[Perd Hapley]

Stand_watie, is that a Flux brand capacitor?

[Stand_watie]

Stand_watie, is that a Flux brand capacitor?

If twas I'd just zip back to Jan 1 and buy myself a couple months to save up my shekels for the a.c. man.

[Jim147]

Did you check for a melted disconnect? If your still getting a buzz noise I would think it is on the high voltage side.

I'm sure all of us would love to be able to fix it over the internet, but it's hard to do with out being able to put our meter on it and get the readings we're looking for.

jim

[280plus]

Got a camera? 

[Nick1911]

Stand_watie, is that a Flux brand capacitor?

I swear to the gods, every single time anyone mentions a capacitor on this forum, someone has to come up with this.

It's not funny or clever anymore, it's just annoying cruft that doesn't help the OP and makes the rest of us 

[280plus]

If you swear at Gods don't you get in big trouble? Or do you just swear to the Gods of swearing? I guess that would be OK. 

[Marnoot]

I swear to the gods, every single time anyone mentions a capacitor on this forum, someone has to come up with this.

It's not funny or clever anymore, it's just annoying cruft that doesn't help the OP and makes the rest of us  

No different than the constant (and always useless to the OP) "use detcord" posts, which you've participated in.