Blower works w/heat but not a/c

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  #1  
Old 05-15-09, 04:42 PM
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Blower works w/heat but not a/c

I just turned on my a/c and the blower fan in the air handler does not come on. There is no problem with the compressor; it runs normally.

I tested the blower by turning off the a/c and putting it on "fan only." There was no response from the fan.

Then I tested it by turning the thermostat up to 90 and putting the heat on (with the fan replaced to "auto"). The blower fan came on immediately, as it has been doing all winter.

But when I switched back to a/c, no blower.

I have a Carrier a/c and electric furnace. Don't they use the same (common) blower fan inside the box in the basement that is the air handler/furnace? I checked the circuit breakers, but they are all okay. Can someone please help me troubleshoot what is wrong? Thanks!
 
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  #2  
Old 05-15-09, 05:58 PM
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Have you replaced the thermostat? Can you post the model numbers of the indoor section, the heater section and the outdoor section? We need to see if you are getting a circuit to the fan relay in cooling or fan only but first need to see the configuration of your system.
 
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Old 05-16-09, 02:57 PM
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Do you have a volt meter?

If so, and if you have one of those open control boards in the handler, you should find where the blower wires hook up to it, and the terminals should be marked as HEAT and COOL, and one or two of the blower wires(if you have more) may be hooked up to PARK terminals. If you put the stat to HEAT -since we know the blower runs then, it is a given that if you used a voltmeter, you would get 120 volts between the HEAT terminal and any ground on the furnace.

Now if you set the stat to COOL, you should similarly get 120 volts on the voltmeter when you test between the COOL terminal on the control board and any ground. If you do, then the high speed windings in the motor are shot (or you have a bad connection between the terminal and the board.

If you do not get 120 volts, then we are back to square one, for the moment.
 
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Old 05-21-09, 03:29 PM
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Sorry it has taken me so long to get back - I had a computer problem as well as one with the ac (keyboard quit working).

Anyhow, here are pics of my system. The model number for the outdoor unit is:
Carrier 38CKC036350 (can't tell if they are 0 or O). (This part works fine.)

Indoor unit heater is:
Radco FA4ANF036 (again, not sure if that is 0 or O).

The a/c air handler part has no visible number ID on it, just the Carrier label.





Ecman, I am at a loss to understand how the high speed windings being shot could make the blower only work with the heat? I was thinking going into this that it was a switch problem somewhere, assuming there is only one blower fan. Haven't replaced the thermostat yet as it is only 18 months old (still could be bad, I know); I was hoping to troubleshoot to make sure that is the problem first.
 

Last edited by pneumaticat; 05-21-09 at 03:33 PM. Reason: get images to show up
  #5  
Old 05-22-09, 04:19 AM
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You still need to check what "ecman" said the blower runs on different speeds for heating and cooling,low speed for heating(hot air is light) high speed for cooling (cold air is heavy) each speed has its own winding.
 
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Old 05-22-09, 09:41 AM
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check for loose wire @ thermostat. did you put a new one in this year? any work done on your basement/walls where thermostat wire runs?

do you know if your system is one where the compressor fires, and then the blower turns on X seconds later? or does the blower turn on the same time as the compressor? since the fan works, assume the circuitry/relay for the blower are ok, but the timer circuit could be bad (bad board). bad timer = bad board = order new one

since the compressor is working, transformer is ok.

what dun11 could be true. to check, there may be a few terminals for L, M, and H fan speeds. without seeing a diagram or pic of the box, i can't tell you much, but there is probably a spade terminal where you can plug the fan input voltage into a L M or H speed plug. ideally, this is the same setting as the heat, so just follow its control wiring. normally though, if an transformer goes, it goes -- not just one output combo. maybe just loose wiring or a short -- or a fuse?

sorry for the rambling post. hopefully you can get something out of my diatribe. good luck.
 
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Old 05-22-09, 11:30 AM
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Thanks for the replies. To answer some questions, no, there hasn't been any work done to the basement or walls where the thermostat wires run. I had a new thermostat installed 18 months ago, which was before last summer. And last year when I turned the system on to test it, I remember that the compressor and the fan fired up at the same time.

See what you mean about the low and high-speed variations. Would high speed apply to the fan-only setting also (since it does not run on fan-only either)? I will have to go buy a volt-meter and test it. I'll probably post another picture of the panel later.

Thank you for the help.
 
  #8  
Old 06-20-09, 10:38 PM
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Pneumaticat, I was just wondering if you've figured this out yet? I came home tonight and turned on my a/c for the first time this season and have the exact same problem as what you're describing. I also have a Carrier a/c and furnace but it's a gas furnace. They are about 20 years old.
 
  #9  
Old 06-21-09, 04:00 AM
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Hi Keith

if you hve a voltmeter, locate the terminal strip in the furncae whers the cables come in from the thermostat and outdoor unit. With the system turned on for cooling, see if you have 24 volts from G to C terminals in the furnace. Can you post the model #'s of the equipment? We can get Carrier wiring diagrams online. Thanks.
 
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Old 06-21-09, 01:21 PM
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I'm not sure if this is the model number (Carrier 305511-201 Rev. A). I've found the same number printed on three different locations inside the furnace. I'll need to find my voltmeter...not sure where it is! I'm going out of town for the next few days but will let you know what I find as soon as I return. Any feedback, advice is much appreciated!!
 
  #11  
Old 06-21-09, 03:39 PM
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I don't see a gas line so the model # for the air handler should start with an F.
 
  #12  
Old 06-25-09, 08:50 PM
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Hi, I'm back. Well, it's hot here... It turns out I've have the manual for the furnace. It is a up-flow gas-fired forced-air Carrier 58GP GS series furnace. The correct model number should be 58GP075-2. I've also found some circuit diagrams in one of the instructions manual. Not sure how to read them yet.

I believe the blower control circuit board isn't the original. It was replaced 5 years ago. Anyway, I can see 6 terminals on the circuit board. They are C, Y, Gc, Gh, R and W. It looks like there are 5 thermostat wires: black, white, orange, red and green. The black wire is connected to the R terminal. The white wire is connected to the W terminal. The orange wire goes through the auxiliary junction box before connecting to the C terminal. The red and green wires are not connected to anything. I think there is a jumper to bridge W and Gh. Since the blower works when I turn the heat on, I assume the Gh is for heat. Then, Gc must be for cooling. But, there is no wire there. What am I missing here? Should I connect the red or the green wire from the thermostat to Gc?
 
  #13  
Old 06-25-09, 10:11 PM
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I've fixed it. It turns out the green wire from the thermostat is for the Gc terminal. I think it came loose when I removed the blower for cleaning last Fall. I figured it out by checking the wire configuration in the back of the thermostat. After reconnecting the green wire to the Gc terminal, the blower works with A/C. Thank you very much for helping....
 
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