A/C Running Constantly


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Old 05-18-15, 04:39 PM
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A/C Running Constantly

After recent A/C activity (changed the condenser fan motor), everything seemed to be ok for about a week (although we did not need to run the A/C for the entire week.)

I noticed that the A/C was running all the time. I can kill it by turning the stat to off and turning the temp up on the stat. Otherwise it just continues to run. The temp seems to stay at the stat set temp - weird right?
I checked the condenser and it was not running- at least not the fan. The compressor would come on every minute or two for a short time and then kick off. So it seemed like we were getting some sort of cold air but it was not continuous (which would explain why it stayed at the set temp and did not go below.

Problem in the stat? or something due to changing the fan motor on the condenser? HELP please!
 
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Old 05-18-15, 05:19 PM
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The condenser fan motor has to run when the contactor coil closes or the compressor will go off on the high pressure limit.

That is very bad for the compressor; do NOT run the A/C until the fan motor is fixed!
 
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Old 05-18-15, 06:45 PM
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Yes I realize the fan not running is not good for the compressor. Like I said in my original post, I just changed a bad fan motor. I had a tech come out because I could not quite get it right. He changed the wiring on the direction and hooked to a single cap for the fan. It ran fine for a few days. But as of yesterday it's been acting like I described and as this person also described http://www.doityourself.com/forum/ai...ting-down.html

Any suggestions? Could a cap go bad so quick? Both are new.
 
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Old 05-18-15, 07:09 PM
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Normally a cap doesn't go bad that quick. I have a feeling it's still a wiring issue.

Did you get a separate cap for the fan motor ?
 
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Old 05-19-15, 04:28 AM
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Yes the fan motor is on a separate cap.
 
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Old 05-19-15, 10:49 AM
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Is the new motor a 3 wire or 4 wire?
 
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Old 05-19-15, 11:05 AM
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skag - it can be wired either way. I think I have it wired as a 4 wire. Brown and brown/white to a cap then black and white to the contactor.

I went home at lunch today and turned on the system. It was running fine. I lowered the set temp 2 degrees to let it run a while and keep an eye on the condenser. The house cooled nicely. But after maybe 20- 25 minutes, the outside unit shut off but the inside blower was still running. The temp never got down to my set temp so it was not turned off the way it should.

I touched the fan motor and it felt hot. So now I know the fan motor works but maybe something else involved with the motor.
 
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Old 05-19-15, 11:15 AM
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fan motor

A 3 wire motor is wired differently than a 4 wire. Sounds like the overload is tripping in the fan motor.
 
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Last edited by skaggsje; 05-19-15 at 11:18 AM. Reason: added info
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Old 05-19-15, 11:23 AM
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I realize that the 3 wire vs. 4 wire is different. I had a tech out and he looked at the wiring. He took the wires off the dual cap and put on a separate cap (he also reversed the wiring for the rotation direction). Mine is wired just as the picture above for four wire (in the upper left corner).
 
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Old 05-19-15, 11:41 AM
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Can you take a amp reading on the motor?
 
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Old 05-19-15, 01:00 PM
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I can do that later tonight...my dad has a multimeter.

After doing some reading, one cause for a motor overheating (although does not seem too probable) is lack of a way for the heat to escape. I noticed screws in the sides of the replacement motor I bought (not screwed in all the way)....they appear to have no purpose. If those are taken out, would that allow heat to escape? I know it's a long shot but I had to ask.

I will get an amp reading later. If the draw is too high...what does that mean? or should I say what could be the cause? The caps are brand new.
 
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Old 05-19-15, 01:20 PM
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Was the replacement motor cross-referenced properly or an OEM motor; perhaps it is not a proper match to the fan load.

Either over or under too far from its proper rating & the motor will overheat.
 
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Old 05-19-15, 01:30 PM
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The place I bought the motor from matched to my old motor specs. The only difference is my old was 850 rpm and the new is 825 rpm which should be fine. It is not an OEM replacement.
 
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Old 05-19-15, 06:36 PM
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I wasn't able to get the meter to read the amp reading. But I noticed on the old motor, it is listed as a 1.5 amp draw and the new one is a 1.9 amp draw? Could that be the culprit? And if yes, any easy fixes other than changing the motor (again)?
 
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Old 05-23-15, 06:04 AM
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I finally was able to measure the amps:

The fan wires to the cap (brown and brown/white) measured at 1 amp. The black and white wires from the fan to the contactor at 2 amps.

I did not let the AC run and measure when it's been running for a while though.

Any suggestions?
 
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Old 05-23-15, 07:04 AM
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You did install the fan blade correctly,air should be coming through the top of the condenser,condenser coils are clean and not restricted,motor is the correct voltage,I may have chosen a motor with more RPM's than less, but that is just me.
Geo
 
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Old 05-23-15, 07:20 AM
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You should have called an HVAC Contractor; that is their job not yours...
 
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Old 05-23-15, 10:38 AM
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Wait...isn't this a "DO IT YOURSELF" forum HVAC contractor????? Thanks for the help.
 
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Old 05-23-15, 11:16 AM
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Posts:18 Wait...isn't this a "DO IT YOURSELF" forum HVAC contractor????? Thanks for the help.
Most forums have safety first policies concerning working on the high voltage electrical portion of an A/C or heat pump.

That forum policy calls for the individual to call a licensed HVAC Contractor to perform such potentially dangerous work. I personally don't want to provide DIY instructions that might lead to them getting electrocuted. Do they have that policy here?
 
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Old 05-24-15, 03:43 AM
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You can be electrocuted with voltage as low as 50 volts with the right (wrong) conditions.
 
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Old 05-24-15, 07:51 AM
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A picture of your old motor tag and of the new motor tag would be of assistance.
What size cap did you buy with the new motor?

Yes the fan motor is on a separate cap.
Did you buy a new cap for your new motor?
 
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Old 05-24-15, 07:59 AM
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Does your new motor list the required cap?
 
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Old 05-25-15, 05:00 PM
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The new motor requires a 7.5. The old was 5. Yes the caps are new. I started with a dual but the tech that I did call (yes I called a tech HVAC Retired) that the replacement motors seem to run better on a separate cap.

The whole system is acting a bit weird. I ran it today for about 50 minutes, the starting temp in the house was 76, it got down to 74 in about 25 minutes and never went past that. The system never shut off. I manually raised the stat temp to 75 and it shut off. Now it will not start by way of the stat (set at 75, temp has reached 75 and not coming on). The fan motor definitely was hot to the touch but never tripped the shut off.

Temps outside when I ran it was 84 and not too humid.

Sound like a stat problem?

And yes I know enough not to get electrocuted.
 
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Old 05-25-15, 10:12 PM
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Do you see any ice on the suction line outside?


Is the larger copper pipe cold and sweating when running?

Is the filter clean?

Can you remove a panel and easily see the inlet side of the coil?

Do you have a digital thermometer to measure the inlet and discharge air temperature?
 
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Old 05-26-15, 08:03 AM
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I was wrong about the issue with the temp. The AC does come on but the issue is it will not shut off. It came on when it hit 76 (had adjusted the set temp to 75) but then keeps on running until I manually adjust the stat temp.

No ice, no sweating, filter clean, a tech was out a couple weeks ago and the temps measured ok on the inlet and discharge temps.
 
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Old 05-26-15, 08:32 AM
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Don't focus on the thermostat. All your thermostat does is A/C on or A/C off. We need to see if the system is working normally.

Set thermostat for at least 5 degrees under the the room temp and let the A/C run.

Does the house temperature come down ?


There is some degree of differential on thermostats. If you set it to 70° the A/C could come on when it reads 70° or 71°. Same with shut off.... you could set it to 70° and it might not shut off until it reaches 69°.

You problem sounds like the system is not performing.
 
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Old 05-26-15, 12:58 PM
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I agree PJmax - I don't know if it's the thermostat. The system definitely cools though. I ran it at lunch and it cools very nicely. It cooled from 76 down to 74 and then sat. It wasn't super hot out (maybe 81) at the time. I do not have a thermometer to determine the true inside temp.

So if not the stat (let's assume for the moment), what other differential diagnoses are there?
 
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Old 05-26-15, 02:17 PM
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This does not sound like a thermostat problem.

If it was overshooting setpoint and cooling down to 72 degrees when set to 75 it would point to a stat problem.

This sounds like a refrigerant problem or you have a return air leak if the suction line isn't cold and sweating when the unit runs.

There is no harm in upgrading your thermostat if you want one but it will probably not help your suction line get colder.

I recommend picking up a digital thermometer or calling a different company to check out your system.
 
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Old 05-26-15, 03:17 PM
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Many valid performance tests have shown that air conditioning systems 'on the average' only deliver to the conditioned areas between 59 to 63% of their Nominal Rated Performance.

It pays huge dividends to check performance as that also just might save the compressor from failing! Indoor airflow also needs to be STRONG; many techs don't even check airflow at all.
Simple easy anyone can do ways to check the performance of your central air conditioner; if needed; you can call an Energy Efficiency HVAC Technician or some power companies may do some of it.

If U want me to run a ballpark analysis of how your system is performing in respect to its ‘Nominal Rated Btuh’ I need at least the following numbers: you'll need to call an HVAC Contractor to fix the problems we find.

You will need to call a good HVAC Contractor to fix the performance problems we find.

Performance Data Collection – Best Time to collect data is late afternoon around +4:30 pm, when attic is HOT; also when outdoor temps are around 85°F to 95°F.

*All U need is a good air-temp probe thermometer (digital reading in tenths preferable) and a low cost 'Indoor Humidity Gauge' you can get at Walmart or most hardware stores or over the Internet.

1) Helpful: condenser 'Tonnage' & SEER Rating of Unit &/or model number:
FIRST; We need to know the 'Indoor' % of Relative Humidity______

2) TXV or, orifice metering device? _______. Only if U know; not critical…

3) Outdoor condenser’s discharge-air-temperature ___°F

Subtract Outdoor air temperature: _____°F

Outdoor Condenser Air-Temp-Split ___°F

4) Need the ‘Indoor’ percent of relative humidity - in the middle of the rooms or, at Return-Air inlet grilles ___

5) Indoor Return-Air Temperature ___ °F

Subtract Indoor Supply-Air Temperature __°F

Indoor temperature-split ___°F

Click-on “Reply with Quote” Fill the #numbers in where the blanks were; then Copy & paste in your Return e-mail or Click-on “Reply with Quote” then write something below the quote so you can send it
 
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Old 05-26-15, 05:37 PM
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So I was wrong about the system sweating. I ran it for an hour plus, I noticed the air coming out was not as cold as it used to after an hour or so of running. The system outside shut off - well the fan shut off but the compressor was trying to run. The grill above the fan motor was super hot. I looked in back and low and behold saw it sweating. No ice but definitely sweating.

In regards to air flow, it's fine. To make a long story short, I recently had all the duct work in our basement replaced, including the return system. A couple of returns had to be cut into the walls/floor because the previous owners butchered the return system. Prior to that I had a home energy audit. All to say, the air flow is good and I put lots of money into the heat/cool system already.
 
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Old 05-26-15, 06:35 PM
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Some pictures might help us identify the problem that your serviceman could not catch while he was there.

The new motor nomenclature and the condenser nomenclature as well as a picture of the wire connections would be a good start.

Did you remember to remove the bottom drain pug on the new motor?

How did you determine that the compressor was trying to start with no fan operation? Amp reading or noise? Intermittent noise or steady?
 
 

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