AC Outdoor Fan Occasionally Stopping

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  #1  
Old 06-30-03, 03:23 PM
sabecker
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AC Outdoor Fan Occasionally Stopping

I have a new Carrier puron central AC system. On some occasions where the AC has run for about 1.5 hours straight, I will hear a noise from the unit that sounds similar to the unit starting (although probably a bit quieter). This tends to repeat a couple times. I determined that this noise is associated with the outdoor fan stopping and restarting approximately 30 seconds later. I cannot tell if the compressor is also stopping, but the flow of air indoors is consistently cool. Is this considered normal operation? Thanks.
 
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  #2  
Old 06-30-03, 04:01 PM
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In hot weather, the outdoor fan should run all the time when the compressor is on. You may have a fan capacitor that is out of spec. and causinf the condensor fan motor to overheat. It has an internal high temp. cutout. It will restart automatically when it cools down. Or there could just be something wrong with the motor. There should be no other reason for that fan to stop.
If the fan stays off for much more han 30 seconds, pressures will rise and the unit may stop on a high pressure safety.

Ken
 
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Old 06-30-03, 07:06 PM
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High pressure safety IF you have one.

Now days it seems they've yanked out all the safetys, If it's cool weather Its the low ambient fan cycle controller. Carrier has a motor controller that will actually slow the rotation to a crawl to keep the right high side pressure, but this is usually optional...
 
  #4  
Old 07-03-03, 12:47 AM
lynn comstock
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It is important to know if the compressor stops or not. If the fan only stops, you should hear the compressor running or humming. If both stop, there should be no noise outside.
 
  #5  
Old 07-11-03, 11:49 PM
sabecker
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Sorry about the delay in posting--I've been out of town. The same problem I described earlier happened tonight when the outside air temperature was 70 F. When the unit shuts down, there is no noise at all, so I figure that the compressor is shutting down as well as the fan. However, when it restarts, it makes less noise than a normal start-up. It is hard to tell if the air coming from the ducts is being cooled as well as when the compressor is running full-time. Again, this only happens after the AC has been running for approximately 1.5 hours.
 
  #6  
Old 07-12-03, 12:39 AM
fanderson1
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It sounds like you have a 2 speed system and it is just "shifting" from one speed to the other.
 
  #7  
Old 07-12-03, 11:17 AM
sabecker
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No, unfortunately it's not a two speed system. The model number is Carrier 38TSA.
 
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Old 07-12-03, 12:43 PM
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Carrier

Not sure on this unit, but it may be one of the new 12 or 14 SEER type units, where they squeeze every bit of energy out of them, to include cooling the condensing unit IAW pressure,( not being dependant on the compressor contactor). Just speculating...
Does the compressor have some type of insulating blanket around it?...Only the higher SEER units tend to do this...I've heard some say you can barely tell if they're running.
 
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Old 07-12-03, 01:31 PM
sabecker
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It is a 14 SEER unit with a blanket around the compressor. When it normally runs, it makes a humming noise that is quite noticeable (although not as loud as some other units). One give-away is that the lights inside my home dim for a couple seconds when the unit restarts after stopping for 30 seconds or so, so I assume that only a compressor restarting would cause that to happen. It did seem like the air coming from the ducts was not as cool when it was doing this, but I don't have the tool to measure the temperature so I can't be certain.
 
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Old 07-12-03, 02:20 PM
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A 14 SEER

with these type units, they operate independant of each other and use a PC board with relays....The big test...Does it keep up on the hot days??? You might just be chasing a ghost!
 
  #11  
Old 07-12-03, 03:47 PM
sabecker
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So it could be more efficient to stop and restart the compressor frequently rather than just let the compressor continually run for the duration of the cooling cycle?
 
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Old 07-13-03, 10:12 AM
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starting cycle...

Just how long are you talking about...Time it with a watch... Carriers inherantly use a 4 min and 45 second time delay between cycles, if it is cycling in between 5 minutes, I'd call back the installer, and have him check out your concerns...If under a year...do it now!
 
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Old 07-13-03, 10:23 AM
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dimming

I have seen new units sometimes try restart before they balance on the off cycle and get caught in a mad cycle on the overload of attempting to start then go off on overload. A Superboost by SUPCO, is available on the market , our cost about $13-$15.00, so expect to pay about $30.00, this will really boost the starting torque. Don't be shocked by the 100% mark-up...jewelry is about 1,700%(a factor of 17) on average... Step one is call in the installer to give him the oppourtunity to check it for you...This would be prudent...
 
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Old 07-13-03, 10:51 AM
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site

see this site
http://www.supco.com/eclass.htm
it will give you an idea of what I'm talking about....some compressors that won't start will with this device because it gives a big jolt to the starting torque...once it starts, there is no problem...
 
  #15  
Old 07-13-03, 03:10 PM
sabecker
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Regarding the cycling times, the unit is silent (and presumably inactive) for approximately 40 seconds. It then runs for perhaps 4 or 5 minutes before repeating. After this happens a couple times, it seems to decrease the amount of time it runs, but I have not yet timed this with a watch. Again, this only happens after 1.5 hours of solid running. The unit has only run for that amount of time in the evenings when it is set to several degrees cooler than the daytime setpoint (on a digital thermostat). I have never seen a daytime run that long simply because it just drops the temperature a couple degrees and then shuts off to wait until the temperature rises again (it has not been extremely hot here yet this summer). I will call the installer tomorrow and ask him to take a look at it, especially since it was installed a month ago.
 
  #16  
Old 07-14-03, 09:44 AM
lynn comstock
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Originally posted by sabecker
It is a 14 SEER unit with a blanket around the compressor. When it normally runs, it makes a humming noise that is quite noticeable (although not as loud as some other units). One give-away is that the lights inside my home dim for a couple seconds when the unit restarts after stopping for 30 seconds or so, so I assume that only a compressor restarting would cause that to happen.
I agree on your conclusion that the compressor dims the lights. The unit should have a delay circuit to prevent the compressor from restarting for a period of 5 minutes. Apparently it is restarting after only 30 seconds. Also when this happens it could be shutting down on a safety device. Setting the stat colder when it starts this pattern of behavior might help you identify whether the stat or a safey is shutting the compressor on and off so quickly.
Why the AC is short cycling after an extended running time is unclear to me.

It did seem like the air coming from the ducts was not as cool when it was doing this, but I don't have the tool to measure the temperature so I can't be certain.

When a compressor starts up it's capacity gradually increases to 100% over a period of 7 to 10 minutes. This is explained at http://www.energystar.gov/ia/product...dAC1-17-01.pdf
 
  #17  
Old 07-14-03, 03:14 PM
sabecker
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At the request of the installer I used a stopwatch to exactly time the cycling today. I set the thermostat to 66 late this morning to assure that the AC would run continuously. At no time did the temperature inside drop below 71, so the stat would not shut off the AC.

The AC ran fine for exactly 2 hours, and then the following cycling occurred:

OFF for 40 secs
ON for 4 min 28 secs
OFF for 43 secs
ON for 20 secs
OFF for 21 secs
ON for 11 secs
OFF for 18 secs
ON for 4 min 28 secs
OFF for 43 secs
ON for 17 secs
OFF for 24 secs
ON for 4 min 28 secs
OFF for 44 secs
ON for 18 secs
OFF for 27 secs
ON for 11 secs
OFF for 18 secs
ON for 4 min 12 secs
OFF for 44 secs
ON for 21 secs
OFF for 27 secs
ON for 4 min 34 secs
OFF for 47 secs

I turned the AC off at the stat at this point, having taken about 30 mins worth of data that just seemed to be repeating.
 
  #18  
Old 07-15-03, 09:32 AM
lynn comstock
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It has to be a safety device.

My guess is the low-pressure switch. If you are familiar enough with wiring and diagrams, find it and bypass it after the short cycling pattern begins. If the problem goes away, this is the switch causing the cycling. The next step is to find out why. This whole endeavor may be a job for a pro.

I also think that the safety circuit is not fuctioning correctly. The minimum off time should be around 5 minutes.
 
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Old 07-15-03, 07:11 PM
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Installed a month ago???

And the INSTALLER told you to time it? He's stalling...If you don't get satisfactory results, ie ,..you think he's feeding you a line of doubletalk to try confuse or intimidate you, call the Carrier rep for you area...If it's supposed to do that, tell him show me in the install manual! It should be stated as such, in the sequence of operations.
Personally I think you might have a freeze stat opening in the air handler that refreezes every time it starts, and it is improperly wired in... ALL safety components are to be wired in series with a timed delay of 4 min 45 secs in accordance with Carrier requirements...
Hard to believe he didn't zoom out there to fix it BEFORE it fails.
PS set it no lower than 72F
Next time it trips, remove the cover panel to the air handler, and see if the coil has any frost on it....it shouldn't!
Did this get issued a permit and inspected by the town inspector? He can be your best friend sometimes...He is there to protect your best interest...not really, but when he does his job,....he inadvertantly helps you out!
Does this also happen when the outside temp is about 80 or higher?
 
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Old 07-15-03, 08:31 PM
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The installer said he will come out on Saturday to fix it--he contacted Carrier himself and tells me that Carrier agrees with me that it isn't supposed to short cycle like it is. The inspector is actually coming tomorrow to do the inspection, so I will ask him to take a close look at things that relate to this problem.

The AC has never run for more than about 1 hour continuously when the outside temp is above 80--simply because I have left it set to 78 during the daytime hours so it never gets far enough above that temp to run for 2 hours straight. If I set it to 74 in the evening (because it has hardly run during the day) to dry and cool the air, it can run for an extended period of time. The specs. for the AC state that the ambient temp. must be at least 55--so I certainly expect flawless operation above 70!

I actually suspect some "computerized" problem (at least in part) simply because this short cycling starts after EXACTLY 2 hours--it could be a concidence but I would guess a timer somewhere has something to do with it.

An air conditioner is designed to be able to run continuously almost indefinitely, or at least for a few hours, right?
 
  #21  
Old 07-16-03, 01:31 AM
lynn comstock
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Let us know how it comes out.
 
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Old 07-17-03, 04:31 PM
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When alls done

Before he leaves, say," Let's test the timer"... With the unit running, set the temp above room temp and see the outdoor unit shut off, when it does, lower the set point in an attempt to start the unit, it should NOT start till 4 min and 45 sec have elapsed. There is a possibility that the unit is under charged or has a leak... this may be why the unit is undercharged
 
  #23  
Old 07-19-03, 03:27 PM
sabecker
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The installer came out to figure out the problem today, and here is what we came up with. The high and low pressures are both fine (he measured with his 410A gauges), and the outside compressor unit doesn't have a computer board in it at all (just high and low pressure switches). We found that when the problem occurs, the wires from the furnace motherboard to the compressor is giving 0 V instead of the 24 V it's supposed to. I actually sat there with my multimeter and watched the voltage cycle from 24 V to 0 V in perfect unison with the compressor and fan going on and off. The thermostat is still calling for cooling the entire time, so I guess the motherboard of the furnace is the obvious culprit. As I understand it, all the thermostat wires go first to the furnace, and then some wires from the furnace go to the compressor.

The furnace is less than 2 years old and was manufactured by Goodman. The parts are still under warrenty, but I will have to pay for labor to swap the board out.

There is no safety in the compressor itself to force the runtime to be at least 4:45, but the thermostat I have won't call for cooling until at least 4 mins have passed since the compressor shut down. The Carrier specs. state that a minimum offtime of 3 mins should be maintained, so I guess the thermostat is doing all it can.

Does anybody have experience with faulty motherboards causing problems like this? Is there any logical reason that a motherboard might try to turn off the compressor and then begin shortcycling after exactly 2 hours have passed?
 
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Old 07-19-03, 05:18 PM
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The furnace is most likely NOT the problem. The compressor wire (Y) comes straight from the thermostat. It may go to a tie point on the furnace board but there is no connection to the furnace there. It is just a terminal put there for your convenience. If the indoor fan does not cycle, I would suspect the thermostat. There are two seperate contacts or relays in the thermostat to turn on the fan and the compressor. I did not re-read the whole saga but if you have an electronic thermostat, try a Honeywell T87 with a heat/cool sub-base. It is the old stand-by and an industry standard as far as I'm concerned. No fancy relays or battery powered circuits. My next try would be to install a jumper from 24v to the Y terminal on the furnace terminal strip and set the indoor fan to run constantly. See if the cycling starts in 2 hours or if the unit continues to run. That would incriminate or eliminate the thermostat.

Ken
 
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Old 07-19-03, 06:36 PM
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I agree

The subbase you'll need is the Q539-1147 along with the T87F round thermostat. Remember, the condensing unit is getting the 24 hot side(red) going throiugh a switch and being recolored as yellow, but it is still actually red(24V hot) traveling down the yellow wire to the terminal strip dummy screw only to get connected to a wire going out to the condensing unit, the other one with it ,is the grounded side of 24V(C). provided its a grounded transformer. If you get 24v from either side to ground (+/-3V) it's a grounded transformer... Next time take your reading at the furnace...if the voltage is lost, it's either a bad wire or Stat.
 
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Old 07-19-03, 07:01 PM
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If you use the Q539A1147 base, be sure to install a jumper between the RH and RC terminals. The furnace you have does not require independent circuits but that sub-base is one of the most popular and will require the jumper. Let us know what type and brand of thermostat you have now so we can try to determine if it is a likely suspect.

Ken
 
  #27  
Old 07-20-03, 01:19 AM
sabecker
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The current thermostat is a LUX Smarttemp 9000. I already called Lux support and the guy there told me he had never heard of one of those thermostats causing a compressor to short cycle. I have an old Honeywell (non-digital) thermostat that I may hook up to test this theory if I can figure out how to wire it in.
 
  #28  
Old 07-20-03, 10:20 AM
lynn comstock
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Use a jumper wire to test

Instead of buying a stat to find out, connect R to Y and G with a jumper or remove the stat and make the connection. If the problem never appears; it has to be the stat. If it does reappear; it must be something else. The regularity of the malfunction seems to be a controlled malfunction and not a random one like a loose connection.
 
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Old 07-20-03, 12:14 PM
sabecker
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Everybody was right--it doesn't seem to be the motherboard at all. In fact, the compressor wire from the thermostat is just connected to another wire that runs out to the compressor outside. These wires are connected near the furnace, but they never actually enter the furnace!

What the installer forgot to mention yesterday was that the location he told me to measure the voltage to see if I had 24 V was actually after the high and low pressure switches. I found where the compressor wire (from the thermostat via the connection near the furnace) itself entered the outside unit and measured a constant 24 V even when the unit cycled off and on. When I measure the voltage after the two switches, it goes to 0 V when the unit shuts off and back to 24 V when it comes back on. I would guess that the culprit must be either the high or low pressure switch--Lynn's first hunch may be the answer when this is all over!

If one of those switches gets tripped, is it normal for both the compressor and the fan (outdoor) to shut off? Does that achieve some desirable function?

I am not comfortable bypassing either of the switches, so I will let the installer figure out why the switches are getting tripped and fix the problem. If anybody has any suggestions as to why either of these switches may be getting tripped only after somewhat extended running, I will certainly mention them to the installer when he returns. The weather has been sunny and in 70's and 80's with significant humidity. The outdoor unit may be getting a bit hotter than that because it is in the sun for part of the day (there is absolutely no way to fix this). However, the inside cooling is not impaired until the unit starts short-cycling.
 
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Old 07-21-03, 05:10 AM
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pressure switch

if its the HP, a constant light mist of water on the outdoor coil from a sprinkler will eliminate the short cycling as a test without using a meter, also a feel on the liquid line (small one) going to the unit would be hot if its tripping, also the discharge air would be really warm to hot. Unless it has noncondensables but even still the water will usually even offset that.
If its low on refrigerant the suction line will not be sweating, (without the water)...discharge air on the outdoor unit will be less than warm.
 
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Old 07-21-03, 10:59 AM
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The high pressure line is very hot immediately after it leaves the compressor, but by the time it exits the unit and passes into the wall toward the indoor coil it has cooled down to the point where it isn't much hotter than the ambient air. The suction line is sweating outside and the indoor cooling is excellent (before the short cycling begins). The installer did measure the pressures after the unit had been running a while (but before short cycling had begun) and said they were normal.

Perhaps either the high or low pressure switch is faulty. I did call Carrier to discuss that possibility with them, but they are not interested in providing technical support to customers (only installers/technicians). If anybody has contact info for the Carrier distributer in the San Diego area and thinks they might be willing to speak with me, I'd appreciate it if you could pass that information along to me.

I am of course working with the installer to get this problem fixed, but the progress has been slow and I have lost some confidence after he left on Saturday blaming the problem on a bad furnace motherboard (which of course is not his problem to fix) without even noticing that the compressor wire never connects to the motherboard.
 
  #32  
Old 07-21-03, 03:05 PM
bigjohn
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Tell him to wire a Tattle Tale device to each switch. TT's are little micro amp fuses with a view window. You wire them in PARALLEL to the safety switch. When the safety switch opens, the current flows thru the TT and blows the fuse which then pops up into the view window for confirmation. Johnstone Supply sells them. Cat # B12-015 for the 24 volts model. You can see them at www.diversitech.com On the home page, click on electrical on the horizontal link bar, then click on time delays/monitors, then click on Tattle-Tale control monitor. You might also find the 007 Control Checker to be interesting. [I don't make up the names]
 
  #33  
Old 07-21-03, 03:47 PM
lynn comstock
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Your voltmeter can determine the cycling switch.

When the switch is cycling and the voltage to the contactor coil is interupted by the cycling switch and turns the compressor off, a voltmeter across the culprit swich will read 24v when it is open (keeping the compressor off).

The fan and compressor cycle together. There is no advantage in having their operation controlled separately.
 
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Old 07-21-03, 04:05 PM
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Tatle tales

these work great on intermittant problems when you are not there to catch them opening. get out the meter and check to see which one is opening, when the cycling startsyou should read 0 volts and then when it opens 24Volts. remember this is reading potential difference. Both sides of the switch are the red (Hot) side of the transformer. When it reads 0, there is no difference in voltage its the same side....R When it reads 24V (the switch is open) its because they're potential is different..
Bottom line the meter will tell the story.
 
  #35  
Old 07-21-03, 05:13 PM
sabecker
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I was going to test the switches yesterday in the manner described above, but I discovered that doing so would require me to dismantle some factory wiring. I don't mind pulling a wiring cap off of where the thermostat wire is hooked into the unit, but I don't want to go any farther than that, especially when a pro is going to have to eventually come fix the problem.
 
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Old 07-21-03, 05:22 PM
sabecker
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Furnace Blower Stopping Too Soon

Yesterday (while troubleshooting my AC as detailed in another thread) I was in the attic measuring the voltage of the thermostat Y wire (the one that controlls the AC compressor). This particular wire is routed through the attic, but never actually enters the furnace unit. I used a digital multimeter in AC voltage mode and found about 5 V between the wire and the furnace chassis. The rationale for using the chassis for the ground was that the wiring specs. for the furnace indicate that the ground wire that passes out to the compressor is connected to the furnace chassis.

I had expected to find about 24 V, especially since that's what I find at the AC unit outside. I redid this measurement a couple of times to be sure I was seeing what I thought I was, but I stopped after the furnace blower paused for about 30 seconds while I was taking this measurement on two separate occasions. Any ideas as to how a simple voltage reading could cause the blower to stop and then restart? There were no other exposed wires I could have shorted.

Now when the AC runs, the blower sometimes shuts off immediately when the thermostat switches off instead of remaining on for the extra minute or so required to blow the rest of the cold air out of the ducts. This is an intermittent problem. Any thoughts as to why?

Thanks.
 
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Old 07-21-03, 09:06 PM
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Moderator note:

New thread merged with original thread for this a/c unit.
Please post questions here to make it easier to follow your problem.

sabecker :

The advice you have been given here should allow you to narrow down your problem.
In this case it may be beyond the scope of a DIY'er and would suggest you put your foot down and get your installer to come and fix it or call a more reputable company if he can't satisfy you.
 
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