My central air system is suddenly acting whacky.

Thermostat and indoor blower are working as normal, activating and running when the temperature rises above its settings, but the outdoor unit does not activate when it should.

I checked breakers and none are tripped. The outdoor motor spins when moved, although not freely (I've never spun it manually before, I don't know how easily it should spin).

The outdoor condenser unit is made by Inter City Products and is at least 15 years old. Still, repair is a much better option than replace.


We are Yankees who transplanted to Columbia, South Carolina. We have adapted to the culture change (as much as anyone could) but have not ever gotten used to the oppressive heat that comes in late Spring.

What other info do you need?

Any advice is always appreciated.

az in SC

 

The outdoor fan should spin like any desk fan would....maybe 5-6 revolutions before stopping, depending on how much force is applied. When there is a call for cooling...can you spin the fan with a stick and it starts and keeps running?

Does the condenser/compressor run? You should be able to hear that. If nothing but a hum and a straining sound (is there such a sound?) And then a click and it stops...I'd guess your capacitor...depending on the answer about the fan.

Common failure item....cheap and easy to replace.

Do you have a multimeter?

 

When I give the fan a good spin, it turns several times, so it clearly isn't frozen, but there is a little bit of resistance. It stops short if i move it gently.

Nothing happens when I spin the fan other than it spinning...the compressor does not start. There is no sign that the unit is working...no hum or any sound, no heat, no vibration. It acts like there is no power to the unit. I haven't checked the voltage (yes, I have a multimeter) as I don't know what to check or the voltages I should expect.

So, what to check next? It's a Saturday, I have all day. Last Saturday it was the water pump in the old Ford Taurus.

 

Well...this may be simpler than the water pump...or maybe not.

This is a contactor.....[ATTACH=CONFIG]890[/ATTACH]


This is a capacitor......[ATTACH=CONFIG]891[/ATTACH]
There are different looks to both of them.

The contactor is a low voltage magnetic switch that applies power to both the compressor and fan.

The cap applies a boost of starting voltage to the comp and fan as well when the contactor is energized.

The contactor has some heavy 240VAC wires that power the big stuff and some smaller 24V (AC I believe) connections that energize it.

The cap has heavy wires that run from the contactor to the fan and comp.


First thing is to see if the contactor is being pulled in when a call for cooling occurs.

Actually, scratch that...first thing is to see if you have 240V to the input side of the contactor. Trace the wires from the power lead to the unit to where they connect to the contactor...you should read 240VAC across them.


I'll be around..and I'm sure some Pro's will be too if they haven't responded while I was typing.

 

Sorry about the delay. I couldn't find the multimeter. After searching everywhere...I found it my daughter's trunk. I used it a while ago to check her taillights. I never put it away. Shame on me.

So the power-in on the contactor is reading 240V..243 to be exact. How do I check to see if the contactor "is being pulled in?" I imagine one of the other wires contains a signal to turn on, right?

Point of information that my help or be really irrelevant. Over the last month or two I had noticed a loud buzzing from the condenser unit when it turned on. Perhaps I should have paid it closer attention.

I'm watching my Gamecocks defending their two-time National Baseball Championship against our arch rival, Clemson right now. I won't be going anywhere except to the PC to check your responses.

Thanks for your help. This remedial step-by-step stuff is great.

 

If you have a helper...turn the stat up above the current temp so everything turns off..then have them turn it down to 65 or so after you are ready to watch. When it kicks in, you'll see the contacts move and hear a click.

You can also push on the contactor with an insulated screwdriver to see if things kick on. You should be able to see the part that's supposed to move? If it starts you have a bad contactor or the control voltage is bad.

The smaller gauge wires are what carries the low voltage. They are thermostat wire size. They are normally on the side somewhere.

Although the nominal is 24V...it should normally read more like 27-28 with no load. If no voltage...might be a broken wire since the internal stuff works.

btw...no A/C Pro here....but I sure do learn a lot from reading what the Pro's type.

 

your fan should be giving you no problem turning by hand, if it feels somewhat tight, even just a little the motor is in need of replacement. now what about your compressor?? does that run at all?

 

OK, test results:

When we turn the thermostat down low, the the blower pumps air through the vents, but the contactor doesn't react at all.

When I depress the contactor, the compressor and fan turn on and begin working.

I checked the voltage across the thermostat wires with the blower on...zero volts. I checked the other end of the wire (on the circuit board of the evaporator) and got 26.7V. When I shut the blower off, I got 0 volts at the circuit board.

Sounds like a bad wire between the circuit board on the evaporator and the contactor, doesn't it?

Good input on the fan motor too. First I want to get the A/C working...then we'll worry about replacing the stuff that fan motor. Comments?

 

Sounds like a broken wire to me....most likely from where it exits the house into the condenser unit.

Just to be clear...cuz specifics are everything..."the voltage across the thermostat wires with the blower on"...do you mean at the contactor?

 

At the contactor, the voltage across the thermostat wires was zero under all test conditions. At the circuit board on the evaporator (big metal box inside the attic through which the air is pumped to and from the ducts) the voltage was zero when the blower was off and 26.7 when it was on.

Am I making sense?

 

Yep....as long as they were the same wires...I'll stick with a broken conductor.

Are you an animal with the weedwacker? Any pets or kids?

First thing I would do is find the control wires where they exit the building and look for damage.


Now there may be some other route the voltage takes...but since not to many others have weighed in...we're probably on the right track. And it's not costing you $100/hr. Lol

How did your team do?

 

I confirmed the wire is the same: Brown outside insulation dielectric, red and white internal. I There is only one wire like it attached to the blower circuit board.

I don't have a weed whacker, but I do have a couple of outside dogs. Inspecting the wire, though, doesn't shed any light on what happened. When I tug on the wire, it is tight and feels like it is stuck between the conduit with 240 and the freon lines. The brown wire itself isn't in a conduit and looks like it was either replaced previously or forgotten when installed originally. We bought the house in '97. I have no idea what the previous owner did with or to the unit.

One more question...do you think it would be easier to pull the new wire down from the attic or up to the attic. I plan to tie the new wire to the old and pull the old one through. I'm guessing down is better, no attic insulation, low ceiling or heat to deal with. Agreed?

My Gamecocks emerged victorious in the 12th, 5-4. Now we wait to see whether we face Clemson again tomorrow afternoon. If they win their game at noon, we'll face 'em at 4. It's still a long road the the College World Series.

 

Ugh.

I replaced the thermostat wire between the blower unit and the condenser, and now I get 25.3V at the contactor. But the condenser still does not turn on when the blower unit turns on. When I depress the contactor manually, the condenser kicks on.

We know the thermostat, the blower assembly and the condenser all work, just not automatically.

Is this now a bad contactor? Can it be the capacitor? Is the contactor a unit specific device? Can I get one at my local Lowes or Home Depot?

 

Durn...I wish a Pro would weigh in.....I hate to be sending you in circles.

It's good that you now have voltage...so there must have been a problem with the wiring...even though that didn't fix the overall issue.

If the comp and fan start when you push in the contactor...then the cap is probably fine. If you wind up replacing the fan later, replace the cap at that time.

It does indeed sound like it must be the contactor. You should be able to test it using your multimeter on the low voltage side....thats if you have an ohms setting of course. Disconnect the low voltage wires and measure resistance across the terminals on a low scale. If it reads 0 (short) or infinite (open) then the coil is shot. I'm not positive on the specs...but I would think around 10 ohms or so would be about right. I'd guess it's open, since you are seeing the voltage....if it was shorted it would probably pop a fuse.

I've never seen one at Low or HD. I don't know whether an Ace or TruValue would carry those parts or not. Normally an HVAC, electrical supply, Grainger, or some appliance parts places is where you get them.

They aren't brand specific but you'd need to get one that matches the specs of what you have. It may look different but would function the same.

You'll need to cut the power to the unit either at the breaker or disconnect. Short across the leads on the cap with a screwdriver or similar, to discharge them. Make a drawing or take pics of where the wires go the remove and replace the contactor.

Hope this helps....

 

It definitely helps.

I figured out a Honeywell unit that will replace mine. It seems like a pretty common unit based on the number of other model numbers it replaces. Now the question is whether I bite the bullet and spend $50+ to ship it over night or try to find it locally.

Thanks for your help on this. I feel like HVAC is no longer a mystery...pretty simple, really. Whoda thunk it?

Go Gamecocks!

 

Local will probably be $15-20 cheaper and in your hand is better than in the mail.

You have a Ferguson HVAC only 8 miles away off I26 (ain't Google maps wonderful)...probably even more options closer. Most places will sell simple electrical parts like that to consumers. And you'll be able to ask questions most likely.

 

Found one at Grainger (also off of I26) for $25. Ordered it. I can pick it up tomorrow.

I doubt they'll have much input, but I'm hoping I won't need it, thanks to your advice.

 

So we haven't heard....whats up?

 

Thanks for asking.

So...I replaced the contactor. When I flip the breaker, the condenser comes on regardless of whether or not the thermostat is on.

The wires from the thermostat read 26V when on, and zero when off.

I'm very sure the wires to the contactor are correct. I may have reversed the thermostat wires, but it doesn't seem to matter if the are connected or not.

Could the new contactor be bad? Is there something else I should be looking at?

Guh.

 

Glad you posted back....sorry it's not working....

I'll PM one of our A/C Pros and see if he can tell us where we went wrong.

I really feel bad that it's not fixed....

 

Not your fault at all. I feel like I know significantly more about A/C than I did before. We came to the same conclusions based on the information.

There is just one little thing I'm missing. Unfortunately I don't know what it is.

Pros may be the answer...but I'd rather hear from them here. A pro in the flesh costs several hundred dollars.

I appreciate your input and the willingness to PM your buddies.

 

ok, I need a picture of your contactor with the current wiring. Did you use a 1 pole contactor or 2 pole? If the unit runs 24/7 and it did not run at all before then you have miswired something. Can you visibly see the contactor is pulled in or not?

 

Agree issue is likely in wiring...though I could swear I got it right.

Single pole contactor. Link to Grainger Contactor

Oddly the contactor does not pull in and the unit comes on. Definitely miswire.

Pictures are a struggle:

That is the right side. It has the black and white 240V wires, and a red wire attached to the connector behind the black.

A single yellow wire attaches on top.

The bottom has yellow and gray (left and right respectively)

The left side screws are red (above)and black (below) behind the red screws are two red wires that combine and clip on the same cinnector as the red screw.

Tell me the error of my ways.

 

With ALL sources of voltage turned off (please use your meter to be sure), remove the wires from the contactor. Check for continuity across L1-T1 & L2-T2. At least one set should read open. If not, you have a stuck contactor. Do you have a model number for the unit? I might be able to get you a wiring diagram online.

 

When I depress the contactor it moves to connect. Do I still need to do your check Grady?

It's just that it is hot, dark and the bugs are out with a vengence tonight .

Tell me I must and I'll do it.

 

Hey guys! I really appreciate you weighing in. If I was wrong in my earlier comments...please let me know.

 

I understand 'bout the critters. The chances of a stuck new contactor are indeed slim. How about a model number of the unit? I might be able to get you a wiring diagram online if the one on the control cover isn't readable.

 

GG, Sounds like you were on the right path. This online troubleshooting can be a bear.

 

The pic is not good enough for me to tell other than you have a wire possibly on the wrong side of the contactor with the black wire coming in from the disconnnect.

 

Here is the wiring diagram:

It is connected as it is shown in the diagram...except one additional spade lug with a red wire connected to L2.

 

Here is a pic of the old one still connected, from the right side

 

That diagram shows a double pole contactor but normally that wouldn't make a lot of difference. Where does that additional red wire connect on the other end?

 

Old contactor continuity test:

L1-T1= open L2-T2= open

when plunger depressed:

L1-T1=open
L2-T2= Contiuity

Hmmmmm


Haven't tested new one.

 

Old contactor is bad. With plunger depressed, there should be continuity L1-T1 & L2-T2. If new contactor is single pole, make sure wires hooked to spades on the "T" side, DO NOT connect to the unbroken "T" terminal. If they do, move them to the other.

 

The mystery red wire goes to a 1" cube shaped box taqht looks like a relay. The other two wires are blue and black...but it's not labeled.

*sigh*

 

We need a Better picture of the whole electrical panel if possible. I know it is miswired but I can't prove it based on your pictures. I would hate to see you spend good money on a simple wire change.

 

This is Grainger's picture of the new contactor. They say it is a single pole. I'm not sure I understand how to identify the difference.

 

If you look at the diagram, that mystery red wire is shown as an orange & is connected to the L2 terminal. If you end up switching the three reds from the unbroken side to the broken side of the contactor, you can put the mystery wire on one of the spades of the unbroken side. Since it is unbroken, it matters not if the wire goes on the "L" or "T" but it must go on the opposite leg from the three. In other words, if the three reds end up on T2, the mystery wire must go on either L1 or T1. Understand?

 

If you look at the right side, you'll see a solid bar between the L & T terminals. On the left side there are a set of contacts under the plunger between L & T. A single set of contacts is a single pole & contactors which break both L1-T1 & L2-T2 are double pole.

 

"If new contactor is single pole, make sure wires hooked to spades on the "T" side, DO NOT connect to the unbroken "T" terminal. If they do, move them to the other."

Take a look at the picture. Is it a single pole? What do you mean by "broken" and "unbroken."

I will try to get full pics of the panel when the light comes again.