Posted: 11/2/2016 12:16:15 AM EDT
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I have a carrier heat pump that has had two issues over the last 24 hours. First, last night I noticed that the outside fan wouldn't start, which I eventually diagnose as the capacitor on the unit. This morning I replaced it, and although the new capacitor is of a slightly different size (same part number from Carrier), everything worked fine. So I close up everything and we are good to go...
Also this morning, I get a "low battery" warning on the thermostat, and end up swapping out the two "AA" batteries. Again, no problem. Tonight, when I set the system to cool, I hear the thermostat switch close, and it tells me that it is turned on and everything is fine, except that I don't hear the outside compressor/fan or the internal fan come on. I go outside, and nothing is running. Check the air handler in the garage and the duct fan is not running either. Setting the thermostat switch to turn off the entire system and turn on the fan, still nothing. I pulled out the battery pack and the thermostat goes blank, indicating that the thermostat isn't getting power from the system. Any thoughts/suggestions for tomorrow? It is 11pm and I'm going to bed with the system off and the windows open. Mike |
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The thermostat usually activates a smaller relay that in turn activates the large "controller" relay. This gets everything running.
I have taken an insulated stick and depressed the controller. If things start, then it could be the smaller relay or the board the thermostat feeds into that supplies the needed voltage to the small relay. Of course, there is always the broken or loose wire syndrome to check too. All the above is true only if you have that sort of configuration. |
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Quoted:
The thermostat usually activates a smaller relay that in turn activates the large "controller" relay. This gets everything running. I have taken an insulated stick and depressed the controller. If things start, then it could be the smaller relay or the board the thermostat feeds into that supplies the needed voltage to the small relay. Of course, there is always the broken or loose wire syndrome to check too. All the above is true only if you have that sort of configuration. I'm going to open the outside unit back up and see if there is a wire disconnected somewhere. The new capacitor was larger and wouldn't fit in the mount. It was next to a set or wires coming in and connected (wire nuts) to corresponding wires from the unit, so perhaps when I closed the unit up there was not enough room and one of the wires was pulled loose. Otherwise I'll probably be calling the A/C company and paying more than I thought I was saving yesterday with my DIY repair. Mike |
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Using a multimeter at the unit, it appears that the thermostat is working - setting the unit to heat, cool, and off appears to provide inputs to the power control board (i.e. inputs are either open or shorted to ground depending on what the thermostat is telling the unit to do. Also, jumpering the R and G at the thermostat mounting plate did NOT cause the air handler to turn on the fan. I even checked to make sure that the air handler breaker/switch was on to eliminate the simple "not plugged in" issue.
One thing that seems funny. Measuring the voltage at the input to the unit, I am only getting 125V AC. I looked at the separate power switch/breaker on the outside of the house, and while the input voltage is 240 (120V each to ground, 240 to each other), the output is only 120V, with one of the outputs having 0V to ground. This goes to a contactor on the outside compressor/fan unit, and the output of that contactor stays at 0V, no matter what the settings on the thermostat are, which obviously prevents power from going to the outside unit. But what about the air handler in the garage? Why won't that thing even turn on the fan? Am I due for a call to an AC repairman, and both a "mea culpa" and a large check being written? Mike ETA: Based on the voltage difference at the outside cutoff, do you think it is possible that the cutoff is bad? I don't see how any of these problems, however, would affect the air handler in the garage. |
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OK, after a visit to the builder's local office and quick discussion, I am 99.9% certain that the service shutoff switch is bad. I was told by one of the folks there that in fact the indoor air handler will not do anything without a signal from the outside unit, so that tells me that I probably only have a problem with the outside unit. A talk with their construction manager told me where to find the 220v circuit breaker panel, and after shutting off the voltage I was able to find out that one of the two lines going through the switch is open whether or not the switch is set to on or not.
Now the problem is that I can't seem to figure out how to get this switch out to see if there are fuses in the back. It appears to be hinged, but will only move far enough to disconnect electrically at the top, and at the bottom I swear it is bending rather than rotating. I cannot determine how it is attached to the back of the box either. The switch and box are Square D, but I can't find any model/part #s, and everything on the internet refers to disconnects with pull outs similar to an automotive fuse (but bigger with a large handle. I disassembled almost the whole box and still can't figure out how to get the switch out other than throwing it on the driveway and running it over with my truck. There's a guy I talk to once and a while that I believe owns a local AC business- if I see him when I walk my dog tonight I'll see how much it will cost for him to send someone over to replace the switch. Peaden wants $90 for someone to come over and do a diagnostic. Mike |
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Quoted:
Do you have 240 at your main panel? Mike 220 phase-phase all the way to the cutoff switch. It is definitely a problem with the switch (hopefully not CAUSED by a problem in the AC unit). With one leg of the circuit open, no power is available to the outside unit. Mike |
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If you think the disconnect has failed then bypass it with a couple of Burnday taps to test your theory.
Burndy Tap |
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Looks like my air conditioning problems are solved (standby for another post regarding an AC problem around 1130pm tonight...)
I got a call back from a technician from the company which installed the air conditioner this morning, and he gave me some good information. When I replaced the start capacitor, the replacement was of a larger size and would not fit on the mounting bracket/strap. When I put the new one in it was therefore unrestrained, and at some point, most likely when the unit started up later, it made contact with an exposed 24v connection on the contactor, blowing a 3 amp fuse in the air handler. This led to no power to the thermostat and to the internal fan not working. Semi-official fix for the short circuit potential? "Leave the capacitor in the box with just the top open/off for the connections." Done. Additionally, a neighbor (guy who lives on my dog-walking route) owns an air conditioning company. He came over this morning, replaced the fuse (I hadn't had a chance to even pull it yet), and confirmed that the shutoff switch was screwy, with the switch not moving all the way to the on position. He got it working temporarily, and we checked that the system as a whole was working, then killed the power again and pulled the switch. He didn't have a replacement, but I was able to buy a whole box with a replacement switch (they don't carry them separately apparently) from a place a half mile from my house for less than $15. Installed the switch in the old box, turned on all the power, and I HAVE A WORKING AIR CONDITIONER, with no charge for the 40 minutes that my neighbor spent going over my system. I told him that I owe him, and will probably try to take him for a local flight in a 172 once I get checked out at the local airport, as I need to start flying again after about 8 months out. Mike |