Compressor not always turning on

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  #1  
Old 07-19-14, 03:56 PM
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Compressor not always turning on

My Ac is about 5 years or less old. It is a 4 ton made by nordyne. Just recently we have had a problem where some times the compressor tries to turn on and won't

you can here the compressor humming and the fan will turn a few times and stop, then turn a few times again stop. maybe does this 4 times while the compressor is humming and then it shuts down. I don't think the compressor is actually turning on. It does develop heat while its trying to turn on.
in the mean time the blower unit will be running without problem except there is no cold air.

if I turn off the breakers and wait five minutes then it will turn on. most times throughout the day everything acts as it should but 1, 2 or 3 time a day we have to reset it.
 
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  #2  
Old 07-19-14, 04:18 PM
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Check the capacitor first, If I were you, put a new one in, capacitor is pretty cheap anyway.
 
  #3  
Old 07-19-14, 04:46 PM
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Yep, capacitor most likely. Just do a search for "bad A/C capacitor". Unfortunately, you probably won't be able to get one on a weekend w/o calling a service company, which will cost way more than the cap itself.
 
  #4  
Old 07-19-14, 05:21 PM
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ok. I'll give it a try. I found one on line. its the same one thats on the unit except its new.

I wasn't sure if the capacitor would work sometimes and not others.

thanks for the advice
 
  #5  
Old 07-20-14, 04:25 AM
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The capacitor helps the compressor start. If the capacitor is going bad, it won't provide as much assistance for starting. When the compressor has been on, shuts off and then tries to start again, it often will be harder to start. The reason is that there is still pressure built up in the system. After the system has sat for awhile, the pressure dissipates and the compressor can start easier. In my opinion, the symptoms you described fit a failing capacitor (one that is starting to fail, not completely failed yet).
 
  #6  
Old 07-20-14, 06:02 AM
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I already have the one I believe is the hard start capacitor ordered. hope it gets here soon because the problem is getting worse.

I did just notice there is a second capacitor. it looks like it was in the unit when it was manufactured and not put on after the fact like the hard start cap.

should I be replacing that ne also or is it most likely the hard start cap and I should just start with it?
 
  #7  
Old 07-20-14, 07:01 AM
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Replace them both is your best bet.
 
  #8  
Old 07-20-14, 08:36 AM
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The start relay should be replaced any time you replace a start capacitor.
If a start relay fails to take the start cap out of the circuit immediately after start up it can smoke the new start cap withing ~ 90 seconds. Start relay terminal 2 to terminal 1 will measure 0 volts when the start cap is in the circuit and ~330 to 370 volts when the relay has taken the start cap out of the circuit.

Start caps usually have a small circular indention on top that will often pop out (or throw debris out) when they fail. Start caps are usually black and made of a plastic appearing material. Start caps usually range from 88 to 400 uF and many capacitance measuring multimeters cannot measure high enough to check them.


Run capacitors often swell on top when they fail. Run caps are usually made of metal. Most run caps range from 3 to 80 microfarad in heat pumps and condensers and can be measured by most meters that can check capacitance.

This slightly swollen cap requires replacement. They do not always swell when they fail but always require replacement when they do swell.


I prefer to measure all of this to identify what requires replacing but the meter can cost more than the new caps.


This little $28 meter measures up to 300 uF and I use it almost every day but I keep a Klein CL2300 that can measure 6000 uF on my tool pouch. I also have a Fluke 902 as a backup. It measures up to 1000 microfarad.

Your best bet is to replace the start kit and run cap.

Capacitors can hold a charge for over 90 seconds after removing power. If you are kneeling in mud and grab one that is still energized it can be a very bad experience.
 

Last edited by Houston204; 07-21-14 at 07:10 AM.
  #9  
Old 07-21-14, 04:57 PM
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ok;
it was not the hard start cap. I replaced it with a new one. the new one came with its own relay. The unit engaged just fine a few times and just now it would not. It was trying to and the fan moved very slow but it would not engage.

so is there another idea I can work with.

I had a tech come out and he said there wasn't anything wrong that he could find. maybe the guy has no idea what he's doing and he missed something or he just wants to sell me a new unit. who knows.

could low refrigerant be the problem? I have noticed the air does not feel very cold though it will cool the place down to 76 deg.

any ideas would be appreciated
 
  #10  
Old 07-21-14, 05:15 PM
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I'm slightly at a loss. In your opening post you said that the fan was running intermittently and you weren't sure if the compressor was running. You replaced the compressor ? cap(s).

What is the fan doing now ?
 
  #11  
Old 07-21-14, 05:47 PM
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the fan is doing the same thing. some times everything turns on the way its supposed to. especially if I turn off the breakers, let the system sit for 5 or 10 minutes, and then flip the breakers back on. it will always work perfect right after that.

then some time after that , everything will try to start. the blower unit in the garage works just fine but the compressor will hum and the fan will make a few slow revolutions then stop. then a few more slow revolutions then stop and do this 4 or 5 times and then the compressor stops humming (I think its trying to kick on but can't) and the fan stops trying to turn on. Right at that point there is a fair amount of heat you can feel.

Then I have to turn the system off at the breakers to get the blower to stop (because the blower will stay on until the thermostat reads the desired temp which it can not do without the compressor working) . I let it sit 10 minutes and turn them back on. the thermostat will read "waiting" at that point. and then when its done resetting it works fine until it cycles on and off 2,3,4,or5 times (different each time) and then the problem starts again.
 
  #12  
Old 07-21-14, 05:52 PM
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and I replaced the hard start cap and its relay.
 
  #13  
Old 07-21-14, 05:55 PM
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Did your tech measure the run capacitor for the compressor and for the condenser fan motor?

Did he check the amperage of the compressor and fan motor and compare them to the nomenclature?

Did he ohm the windings?

Did he list this information on your invoice?
 
  #14  
Old 07-21-14, 06:40 PM
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I can't say exactly what he did. I Know he said he did a full diagnostic and everything looked good. I watched him for a little while and he was testing things with meters and pressure gages.

I can only assume he tested everything.
 
  #15  
Old 07-21-14, 06:52 PM
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Did you replace the run capacitor ? .
 
  #16  
Old 07-21-14, 07:51 PM
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It sounds to me like this unit needs a run capacitor.

It is a shame if this tech didn't measure it with these symptoms but I have my doubts.

Bet cap readings are not on the invoice.:NO NO NO:
 
  #17  
Old 07-22-14, 03:44 AM
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my run capacitor has these numbers on it (I won't pretend I understand them all)
370va
10000afc
45+7.5 uf

and e237947 (is this a part number)
 
  #18  
Old 07-22-14, 05:15 AM
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You have a 45 plus 7.5 microfarad by 370volt dual capacitor.
It serves both the fan and compressor.

45 + 7.5 uF 370vac dual cap.

If you replace a round cap with an oval cap you might need a piece of plumbers strap and two 1/4" hex head self tapping screws.
 
  #19  
Old 07-24-14, 04:00 AM
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this is the one I have on order. should be here in 2 more days. Is it correct?

GE Genteq Capacitor Dual Run Round 45/7.5 uf MFD 370 Volt

how do I bleed off power from the old run cap to keep from getting shocked?
 
  #20  
Old 07-24-14, 05:12 AM
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Turn off power and wait 3 minutes.
I usually then push in the contactor to prove power is off and bleed off anything left in the cap.
Test with a screw driver from the cap terminal to ground.
Write down the connections since it is a dual cap and then replace.
 
  #21  
Old 07-25-14, 07:00 PM
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I'm not certain if the compressor has been doing this the whole time but I just noticed that it is also shutting down some times after a successful start.

so everything will start up like its supposed to and then the compressor shuts itself down. I just happened to catch a light blinking. From the panel it seems to be flash code 5 which is "open circuit"

Does that seem indicative of a bad run capacitor also or maybe something else?

the new capacitor should be here tomorrow
 
  #22  
Old 07-25-14, 08:30 PM
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If the contactor is staying engaged then the only reason the compressor only would stop running is if it was overheating and shutting down on thermal overload. That is not a good thing. If your fan is running ok then possibly the problem is part of the capacitor issue
 
  #23  
Old 07-26-14, 04:36 AM
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When the compressor starts up normally most times it runs just fine for a while. I have set the ac to 71 to see if it would cool down that far and everything ran and ran just fine.

the times I noticed the compressor had stopped after a successful startup it seemed to happen shortly after it started.

Up until not I thought the only problem was the compressor would some times not start up.

The fan either runs or doesn't run depending on wether the compressor iix running or not (compressor running equals fan running. compressor not running equals fan not running)

I guess this may be because I have a dual run capacitor?
 
  #24  
Old 07-26-14, 07:15 AM
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Post the model number of you Nordyne outdoor unit.
 
  #25  
Old 07-26-14, 12:15 PM
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it is a nor dyne ft4bf - 048ka 4 ton
 
  #26  
Old 07-26-14, 02:15 PM
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Just noticed something else rather odd. At least I think its odd but I have reason to believe it has been acting this way the whole time.

The AC was set at 72 (that is much lower than normal for us) I noticed that the AC had been running for some time and I looked at the thermostat and the room temp was 77.

That means the compressor had shut down (or possible never re started in the first place) and the blower had been running the who time.

When I went to trip the breakers I noticed the outer unit was running. And the house is getting cooler.

so the outer unit shut itself down before the thermostat hit the set 72deg (thats why the blower was still running) and after some period of time the compressor started working again.

not sure if that helps give a clue to the problem. I received my run cap today and I'm going to install it when it cools off
 
  #27  
Old 07-26-14, 05:14 PM
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http://www.nordyne.com/literature/708367b.pdf

Flash Code 5

1. Outdoor unit power disconnect is open
2. Compressor circuit breaker or fuse(s) is open
3. Compressor contactor has failed open
Check compressor contactor wiring and connectors
Check for compressor contactor failure (burned, pitted or
open)
Check wiring and connectors between supply and
compressor
Check for low pilot voltage at compressor contactor coil
4. High pressure switch is open and requires manual reset
5. Open circuit in compressor supply wiring or connections
6. Unusually long compressor protector reset time due to
extreme ambient temperature
7. Compressor windings are damaged
Check compressor motor winding resistance
 
  #28  
Old 07-27-14, 04:52 PM
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the capacitor I received was not the correct one. So I just called a different ac guy.

He first said he turned on the system and it was working fine except that the difference in the in coming and out going air temp was not enough so He felt it needed refrigerant but there was no reason he could see that the compressor would not start or turn off.

I told him something had to be wrong. He then mentioned the run cap did seem a little weak so I told him to replace it.

$259 later, we left the house for 3 hours with the ac running. when we came back the ac was not running and the thermostat was blank with no power.

the breakers were not tripped.


so now I have no idea what to do. The only thing I can think of is to go and find my wifes friend who talked her into wanting to hire the jerk who sold us this thing and smack her. but that won't really help
 
  #29  
Old 07-27-14, 05:26 PM
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Intermittent problems can be tough to repair if it doesn't occur for the tech while he is there.

I'd call that tech back to fix it. You might see continued labor but you shouldn't be charged a trip charge.
 
  #30  
Old 07-27-14, 05:38 PM
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Could the problem be the batteries in the thermostat? Because I was going to run out to home depot befre they closed and get a new one. I figured it couldn't hurt to replace the thermostat. when I started taking the thing off the wall I found that the batteries in it (3- AAA) were swollen and the contacts corroded.

So i cleaned the contacts and replaced the batteries and the thermostat came back to life. Right now it says "waiting" so the system is re setting. I have my fingers crossed


and it just now turned on. Will it keep working properly?
 
  #31  
Old 07-27-14, 06:59 PM
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Your trouble code could be caused by weak batteries in the stat.
Are the terminals in the stat green and corroded at this time?
 

Last edited by Houston204; 07-27-14 at 07:42 PM.
  #32  
Old 07-27-14, 07:11 PM
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no;
I just pulled the therm. off. it like plugged into a panel behind it.

it does not seem to have been the problem. It must have been a coincidence. the ac worked fine for a while. It got town to 76 deg and 51% humidity and then it she off.


then it never came back on. I took the panel off and none of the led's that were always on were on any more. A lot of water on the ground and it looks like the coper lines to the compressor had frost on them. Looks like it had been melting.

the filters are clean and recently replaced.

Just wanted everyone to know I really appreciate the advice I have received here.
So far nothing has worked but I appreciate the effort.

thanks
 
  #33  
Old 07-27-14, 07:44 PM
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Your stat could still be the culprit.
It is not hard to bypass a thermostat to verify this.


Turn off power to the indoor unit, pull the stat cover off the wall and remove 4 wires to allow you to twist them together to bypass the stat.

The R,G,Y and O wires must be twisted together with a wire nut for cooling.
 
  #34  
Old 07-29-14, 06:36 PM
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I tried a new inexpensive thermostat. it didn't help

I called the tech back out. luckily this time the AC was having one of its fits and was trying to start up just when he got here.

He says the compressor was turning on but the fan was not. there is some round box with a relay or something in it. he says that is probably bad. He ordered a fan ale to be safe because the parts have to come from out of state. (no nordyne around here any more)

So it seems the compressor was coming on but the fan was not and the compressor was shutting itself off because of over heating. the humming noise I heard was the compressor running. Not the compressor trying to start up. thats what he says any way

make sense?
 
  #35  
Old 08-04-14, 06:23 AM
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I think it may start the compressor and outdoor fan cause the compressor to reduce the capacitance does not work, I suggest you replace two capacitors, the price is very cheap. Also check the thermostat is not damaged.
 
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