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Old 11-14-2010, 02:17 PM   #1
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Question Cycling on the basement A/C

I have the basement heat pump. I am hooked to 50 amp power and the furnace works just as it is supposed to work. The problem is the A/C. I can turn on the air conditioning in the morning and set it to 75 or so. When the temperature in the rig gets to the set point then the A/C comes on, both compressors, and runs just fine. It will cycle on and off as necessary to hold the set temperature and run all day. Generally in the evening we will move the thermostat down to 70 degrees so that it is more comfortable to sleep. This is when I have the problem. The heat pump will run for about 5 minutes and then shut off even though it has not reached the set point of 70. Then in about 5 more minutes it will turn back on and run just fine with cold air for another 5 minutes. It continues this until it gets down to the set temperature. I am satisfied that the problem is not icing because I have had the A/C turned off all day and just turned it on at bedtime and had it immediately repeat the same problem. We are in Arizona so it is pretty dry here as well. I am satisfied that the problem is not the heat pump and was leaning toward the thermostat but now I am wondering if there is a sensor that is the problem. But the A/C, and the heat cycle, works fine if there is only a degree or so between the set point and the room temperature. In fact the A/C can get to where it is several degrees behind the room temperature and it still keeps running continuously. The problem is only when I manually turn the thermostat down several degrees from the room temperature. Does anyone have any ideas what is going on? I would really like to get this fixed.
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Old 11-14-2010, 02:33 PM   #2
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Doug, Your post says that there is no problem when the set temp is near the room temp but you do have a problem when the set temp is 5* lower than the room temp. When the set temp is 2* different from room temp only #1 compressor operates. When the set temp is more than 2* (maybe it's 3*) both #1 and #2 compressors operate. The fact that it shut down for a few minutes indicates something that is working with the #2 compressor is overheating. It cools down then restarts. I would suspect the #2 compressor relay....it's in the upper right hand section of the electronics compartment. It's will be a rectangular component with 4 or maybe 5 wires connected to it. There are 2 of them. The #2 relay is the second one down from the top.
You said that both compressors are operating during the day when set to 75*. How do you KNOW both compressors are operating? If it is maintaining the set temp only #1 will operate.
Open the A/C electronics on the left side of the unit itself with power disconnected. Look very carefully at all components and connections. Perhaps you'll see something that looks like it has overheated.
Be sure you let us know what you find.
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Old 11-14-2010, 04:24 PM   #3
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I can feel and hear each compressor start. I guess the second compressor could be running for a few minutes and then stop but I am fairly sure that it is not cycling during the day. Also, when it cycles at night after the setback, the entire unit stops running. It shuts down entirely for 5 minutes and then each compressor starts back up. At least one compressor and probably two compressors are running continuously during the day.
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Old 11-14-2010, 05:16 PM   #4
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I'm hearing what you're saying. The way I understand the tstat is designed to operate is once it cools to the set temp and shuts down then only #1 runs unless the temp rises more than 2* (maybe it's 3*). So, if, after cooling to set temp and shut down then restart because it warmed up #1 should be the only compressor running unless that one compressor can't cool enough........then #2 starts. What you describe is not this (as I understand it) design.
Have you looked at the electronics yet? What did you find??
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Old 11-14-2010, 06:04 PM   #5
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My air conditioning does not get down to the set temperature in the evening until it has gone through 5 or 6 cycles of running for 5 minutes and then being shut completely down for 5 minutes. During at least the first few cycles I can hear both compressors start which they should do because the set temp in 5 degrees above the room temp.
I'll try to check the electronics tomorrow but I think they are fine since it runs fine during the day and it puts out lots of cold air in the evening too.
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Old 11-15-2010, 09:33 AM   #6
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It might be a flaky indoor coil thermister. You might try jumpering it when the system is short cycling at night.
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Old 11-15-2010, 05:06 PM   #7
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Can you try setting it down only 2 degrees at a time and see if it seems happy? If so that would tend to implicate the 2nd compressor (because you'll only be using the 1st compressor with a 2 degree difference).
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Old 11-15-2010, 05:32 PM   #8
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I had the same problem on my 2002 Journey. I had asked for help on this site and got information about moving the thermister from one side of the coil to the other side. Once it is moved you should be able to see it when you remove your filter. I had the dealer move it for me and it worked. No more short cycling. Hopefully someone else can give you more details about this. I believe they had to drop the unit to get at the thermister. Two other things that can cause short cycling are a dirty filter or a vent blowing on the thermostat. Good luck. John
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Old 11-18-2010, 07:41 AM   #9
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Well, I had a qualified, experienced Coleman/RVP serviceman come out and check out my A/C. The capacitors and other electrical all checked out perfectly as did the sensors, freon and thermostat. They talked to Coleman who said that short cycling will happen when the outside temperature is in the 75* to 80* range or less. Their solution is to turn off the breaker for the second compressor and just run it on the first compressor when it isn't really hot outside. (Royal pain) The strange thing in my case is that it didn't used short cycle at these temperatures and now it does. Anyway, another possibility is that it works fine when the sun is shining on the radiator and short cycles when the sun goes down. Maybe the sun keeps the thermistor, or freeze sensor, warmer so that it doesn't shut down. Interestingly, I did try running the A/C last night when it was about 70* outside and it shut down after a few minutes. I then then turned off the breaker for compressor #2 and it ran just fine until it reached the set temperature. I think this proves that the issue is in fact that the thermistor is reaching the set point of about 38* and shutting down the A/C. As soon as it warms up the A/C starts up and runs again until the thermistor gets too cold again. But as I said earlier, the thermistor checks out okay electrically.
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Old 11-18-2010, 08:01 AM   #10
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Personally I wouldn't be satisfied with that answer, particularly knowing that this is a new problem. Something else to check is the indoor coil......maybe it needs to be cleaned. If it's not allowing full air flow that would cause it to get cold quickly and shut down the unit.
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Old 11-18-2010, 08:14 AM   #11
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They said the coil was fine and there was good air flow.
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Old 11-18-2010, 09:46 AM   #12
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Quote:
Originally Posted by Doug Sage View Post
Well, I had a qualified, experienced Coleman/RVP serviceman come out and check out my A/C. The capacitors and other electrical all checked out perfectly as did the sensors, freon and thermostat. They talked to Coleman who said that short cycling will happen when the outside temperature is in the 75* to 80* range or less. Their solution is to turn off the breaker for the second compressor and just run it on the first compressor when it isn't really hot outside. (Royal pain) The strange thing in my case is that it didn't used short cycle at these temperatures and now it does. Anyway, another possibility is that it works fine when the sun is shining on the radiator and short cycles when the sun goes down. Maybe the sun keeps the thermistor, or freeze sensor, warmer so that it doesn't shut down. Interestingly, I did try running the A/C last night when it was about 70* outside and it shut down after a few minutes. I then then turned off the breaker for compressor #2 and it ran just fine until it reached the set temperature. I think this proves that the issue is in fact that the thermistor is reaching the set point of about 38* and shutting down the A/C. As soon as it warms up the A/C starts up and runs again until the thermistor gets too cold again. But as I said earlier, the thermistor checks out okay electrically.
Doug, You're the one that said that it never used to have the symptoms it now has. So, something has to be different.
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Old 11-18-2010, 10:42 AM   #13
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I agree that something is different. The issue is that Coleman says this is normal for this temperature??? and I am guessing that moving the thermistor around might help as another poster suggested. The problem with that is that apparently you have to drop the unit to move the thermistor and it would be a hit and miss proposition as to where to move it - up, down, left, right. It could cost me a lot of money to have that done. If Coleman could tell us exactly what to do then I would probably pay to have it done.
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Old 11-18-2010, 10:47 AM   #14
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Doug,
Removing the unit is really pretty easy. Look for a post on here by Duner. The unit can be run while on "blocks" and out of the unit. There is no electrical to disconnect. If you feel like you could do the job but don't have the strength then hire a couple of young guys to help move it out. If you can't do it yourself then I agree with you when you say that it's going to get expensive.
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