Compressor Cycling On & Off

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  #1  
Old 11-12-07, 03:25 PM
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Question Compressor Cycling On & Off

Did a general search on AC Compressors cycling on & off before posting this question. While I did find several that addressed this issue, I still wanted to get some fresh feedback.

Have a three year old Carrier unit (15 SEER, using Puron) that when I turn down the thermostat to bring on the AC, my outside condensing unit begins to cycle on and off. Specifically both the outside unit (compressor) & fan on top of the condenser (not to be confused with blower motor) turn on for about 1 minute, then stop for ten seconds only to both turn on again. This will happen maybe 5-6 times and then the AC condensing unit will remain on until the requested thermostat temperature has been reached.

Today I removed both the start/run capacitor & contactor and ran over to Grainger for replacements. They had the capacitor but not the contactor which I will pick up tomorrow.

Replaced the run capacitor and reinstalled the original contactor, turned on the power, lowered the thermostat and the same thing happened again. Both the outside condensing unit compressor and fan turn on only to shut down for a moment and then turn back on.

Did check my high side line (the line wrapped with the insulating material) and it is getting cold and showing signs of sweat & condensation.

What else do I need to check? Am I low on freon (Puron)? Could this be a thermostat issue? I'm in a rather large house with multiple zones so swapping out the thermostat with the exact same model is easy. Can't imagine that a three year old unit is acting up but apparently so.

I live in Texas where today's high in Dallas was in the 80s. Same is forecasted for tomorrow.

Thanks in advance for any suggestions.

David
 
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  #2  
Old 11-12-07, 04:24 PM
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HI dp:

The insulated line is the low side line. How cold does it get? Cold or COLD? Once the unit gets running is the line cold or COLD? Can you post the model #? I'm thinking that your system might be ok but with the little bit cooler weather, the low side refrigerant pressure control is cycling until the refrigerant flow is established. Are all the zones calling for cooling or just some? That would exacerbate it. If this is indeed what is happening, the fix is what we a low pressure bypass control. This is a timer which temporarily bypasses the LP control and lets the unit for a coupl;e minutes until it gets flow established. Has this happened before? If not, you might have a refrigerant shortage. which would of course mean a refrigerant leak.
 
  #3  
Old 11-13-07, 08:31 AM
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First off, thanks much for the reply to what I'm sure is a tired subject. To answer your questions the Carrier model # is:

38ESA030300

The low side line is getting cold but probably not ice COLD.

As for my other units at this time of year, even with a warm Texas November I don't have them on since no one is at home during the day. I typically turn the thermostat way down at night for restful sleeping in the upstairs (kid's rooms) and then in the master bedroom - which is where I'm experiencing the problem.

Getting ready for bed last night I put the thermostat down and went outside to watch the condensing unit. Same thing occurred with the cycling on and off. After doing this possibly ten times the unit stayed on until the master bedroom cooled down to the set temp.

As you suggest I believe I'm low on Puron which spells leak.

I called my AC guy who agrees I'm probably low on refrigerant. This has never happened before on this unit or any of the others in my house.

My last question is may I run the AC at night until my service guys shows on Thursday? With it presumably low on Puron, will that harm the compressor?

Again, I appreciate the assistance.

David
 
  #4  
Old 11-13-07, 02:38 PM
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Couple things here...

First you can buy a Carrier with no safty controls at all. Why anyone would when a simple leake can lead to a very expensive repair is beyond me.

Since the unit is cycling before finally running could indicate that you have a low pressure switch causing this symptom until the flow gets going.

But if the unit does have safties it should also have a lock out control. A lock out basically sees that the compressor should be running. If the lock out thinks the compressor should be running and is not, then it shuts the unit down untill control power is terminated and then restored.

Unfortunatly, I'm getting a server error on Carrier's tech site and can't log in to check the wiring for your unit at this time.

That said, you maybe low on charge. The compressor should normally stay off for at least 3 minutes before a restart to allow high side and low side pressures to equalize.

But if you are low on charge this "may" not be an issue until your tech gets there. Meaning that I think it maybe safe to run it. However if you can do without until it is checked out, do that.

When the tech does get there have the logic board (lock out) checked. You maybe low on charge AND have a bad lock out circuit.
 
  #5  
Old 11-13-07, 04:06 PM
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I spent a fortune upgrading to these Carrier units and to find out they have no safety built in really burns me. Plus, they are louder than hell which I've not cared for since the day we moved in. Next house we build I'm going to specify the exact make and model of the outside condensing unit.

Too bad the Carrier server is down. Would love to see what you pull up for my malfunctioning AC. Where would a low pressure switch and lock out control be located? The only panel that I see accesses the run capacitor and contactor only.

Thanks for your reply!
 
  #6  
Old 11-13-07, 04:35 PM
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Re-read my post

I said that the fact that it is cycling tells me that it does have safties.

The fact that it is not locking out points to a logic board (lock out) not working.

Just tried again still a server error.

"louder than hell"? If all units are like this (loud) could all be under charged to some degree or improper installs. A compressor with not enough gas to compress can be loud and have little oil coming back to lube it. Bad.

When you remove the large panel to get into the elec panel you should see the compressor.

Big pipe and small pipe coming from the black compressor. Somewhere on each line is a small 1/4 inch tube with a black plastic thing on top with two wires coming out. Big line is low pressure, small line is high pressure. There may also be a high temp safety but save that for another day.

I hope you are killing power to this thing to keep it from killing you!

The logic control (lock out), it's called logic because it sees the compressor should be on but is not - logic says something is wrong so it will stop everything.

It's a board about 2 by 4 inches. Follow the compressor leads. One (black) will go through an alluminum "oval loop" on the board. This sences current going to the compressor. It's looking for current to prove to itself that the compressor is running or not when it should be.

Don't be so down on Carrier, while I probably wouldn't by it for my house it is a high end product. And very reliable, I maintain Carriers 40 and 50 years old. Virtual tanks like Lennox.

When you add the "loud" statement it makes me think you have some issues with the Master Bed unit and install issues all around.
 
  #7  
Old 11-13-07, 04:46 PM
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I went to www.carrier-commercial.com and found your wiring diagram. It shows safety controls and an * indicates when/if installed. Since the unit is cycling, most likely your unit has the safety controls from the factory. However, Jarred is right, Carrier units with safety controls usually also have the CLO [Compressor Lock Out] feature as well. If your unit does in fact have a CLO. it's possible someone bypassed it coz they didn't understand it's operation. With a CLO, a safety control opens once the unit locks out. I'm still wondering if this has happened before because it's weird that the unit would eventually take off and run. That could be a sluggish TXV problem. Carrier has had some problems with TXV's on Puron units. Usually if a system is low on refrigerant it won't catch up to itself and start running ok. It's also possible that the low pressure control has lost it's calibration.
 
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Old 11-14-07, 08:20 AM
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Jarred & John, again I appreciate your help. Apparently I'm one of those guys who knows just enough to get myself in trouble. I'm glad I've called my HVAC guy out even though I'll certainly be cutting him a big check.

First off, I don't like putting a 9 volt battery on my tongue (something we did as kids...) much less getting bit by AC current. You bet I turn off the breaker before working on these units!

Ok, I'll cut Carrier some slack even though there has been noise problems associated with all three units since the day we moved in. I firmly believe that we've been the victim of poor installation and the loud running units continue to this day. After I escalated our woes one of the more senior techs traced the problem to a lack of Puron and he added more. That silenced the units a little but not enough for my taste. They've also tried to shake & pull the copper tubing and rearrange the placement of the condensing unit on the cement pad. Very odd ways of addressing the problem in my estimation that have not worked to date.

I even contacted Carrier who recommended some sort of an insulating sleeve for the compressor that's designed to quiet it down. Problem is (as I was told), this sleeve makes the compressor run hotter which possibly compromises its useful life. I said no to the sleeve as compressors aren't inexpensive.

All three seem to surge or 'hum' which translate in to a vibration or noise that can be clearly heard in the master bedroom as unfortunately the units are installed outside the master bathroom! Something when I design our next house will never happen again. Regardless of the cost of copper or the loss of efficiency, all outside condensing units in our next home will be placed near the garage or as far away from living areas as possible. Sorry for the rant but each summer my wife and I have to get used to the droning of the units as we sleep.

After my HVAC guy comes out tomorrow I'll post back and let you know what the diagnosis was.

John, what do you mean by: "Carrier has had some problems with TXV's on Puron units". I'm not familiar with TXV.

Thanks!

David
 
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Old 11-14-07, 03:17 PM
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First David, whomever you talked to at Carrier maybe misinformed. The "sleeve" is called a compressor blanket. It fits around the compressor and closes with velcro. Carrier makes units with a blanket on the compressor at the factory.

Being more commercial I havn't heard of Carrier having TXV problems but it is certainly possible.

I understand about the units being right outside of the master. Bad location. If your going to be there a few years get qoutes to move them. Might end up being a selling point.

John, do you have Carriers HVACPartners? I'm still getting a server error.
 
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Old 11-14-07, 03:43 PM
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Jarred,

Won't the compressor blanket make it run hotter and shorten the lifespan of the component? I'll order blankets tomorrow if you say it's not so. I live in the great state of Texas where 110 degree summers are commonplace.

Also, what does TXV stand for?

Thanks!
 
  #11  
Old 11-14-07, 04:17 PM
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The compressor blanket is put on the compressor to deaden the noise. You can also add discharge line mufflers to further reduce noise. Both of these are installed in the manufacturing proccess.

I guess it could be said that the condenser fan aids in compressor cooling but that doesn't do the whole job.

What really keeps the compressor motor cool is the suction line gas coming back. The large insulated line at the outdoor unit, the cold sweating one, the cool refrigerant in that line cools the compressor motor.

It doesn't matter if you have a 3 ton, 5 ton, 20 ton roof top, the suction gas coming back from the evaporator is what cools the compressor.

A blanket on the compressor matters not, it's job is to deaden the compressor noise, that's it.

If I could get on the site I could probably get you the part number. While there are "universal" blankets there are also compressor specific blankets, made to fit.

You can also move the units as I said. I've done it 5 times, not for work but for friends.
 
  #12  
Old 11-14-07, 07:53 PM
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I just use www.carrier-commercial.com with no problems. It's a public website.

Thermostatic Expansion Valve = TXV

It's a valve that meters the refrigerant into the evaporator coil when the unit is running. I've seen on some of the pro websites that Carrier has had some problems. Check out www.hvactalk.com Just don't ask any DIY questions there. The guys get a little testy.
 
  #13  
Old 11-16-07, 11:44 AM
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Well, I was down over 5 lbs. of Puron which was not cheap to refill. Since that obviously spells leak, my HVAC guy got out his cool 'sniffer' tool to nose around to see where it might be coming from. I've known for a little while that the main condensate line going in to one of my downstairs sinks was clogged. What I didn't know was the backup condensate drain was leaking rusty water on my brick!

I thought that for sure spelled a leak in my evap coil but even after closer inspection the sniffer couldn't find anything. I do have some work in front of me this weekend to cleanup all the rusty water out of the bottom of the evaporator coil and drain pan underneath for the secondary condensate drain.

Glad I only parted with $250 and not $1,500 for a new coil.
I'll certainly be calling out the HVAC guy again before summer starts just to top off that unit and look at the other two.

I likely already know the answer to this next question given a few of the stickies on this site, but can anyone off the street buy Puron or only licensed HVAC pros?

I've got some nice new gauges and other freon (green cannister) but no Puron.

Thanks again for all the assistance and direction.

David
 
  #14  
Old 11-16-07, 03:07 PM
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Cool

No, you can't buy it. You'll have to have an EPA license. While the license is pretty easy to get (there even online testing sites) if you don't have the HVAC training and take too much into your own hands you may do more harm than good.

$250 isn't a bad bill for 5 pounds and a leak search. But 5 pounds is a lot!

Personally, I get pretty ticked off when I have to charge a unit, know there has to be a leak, and can't find it. When that happens I put dye in the system and either come back in a week or so, or wait until I need to "top it off" to search again. The dye shows up very bright almost yellowish green under the UV light. Think black light poster.

So, call that company back and ask if the use (or know of) dye, you may have to call around to find a company who does use dye. Put it in all units, to find this leak and any future leaks in the others.

You may also want to try and figure out where the linesets are in the walls. Any long nails or screws from the inside or outside in that area?

The puron when somewhere and leaks don't get smaller. Could be the gauge ports (very common), evap coil, or braze joints when it was installed.

You need to find it and fix it.
 
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