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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8435
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a 4year 10 month old Carrier heat pump a/c system,

Customer Question

I have a 4year 10 month old Carrier heat pump a/c system, model no. 25HCC548A300. Today when I returned home, the thermostat was completely off with no numerals or information showing on it - just a blank unlit screen. The system was completely not operating. As we live in Florida we keep our thermostat setting at 69-70 degrees from May-September. The outside unit as well as the large portion of the unit under the house was not running either. Could you please tell me what the problem could be. Is there a reset switch on the thermostat, a reset switch on either of the outside units, etc. For your information the circuit breaker box for the whole house was checked and the 2 circuit breakers for the a/c system had not tripped. Thank you very much. ***** *****
Submitted: 1 year ago.
Category: HVAC
Expert:  Tim H. replied 1 year ago.

Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Please provide all information I request as it makes it more difficult to troubleshoot something when I'm not there onsite. Essentially, you become my eyes and ears. Thanks for the opportunity to help. At the end of our dialog, you will have a chance to rate my service, but please wait until we are finished and you're satisfied you have all the information you need.

Sam, since your inside furnace or air handler supplies power to the thermostat, check that. Check the circuit breakers (for inside unit), on-off switch on the unit itself, and finally if all that is OK< check the control board for a blown fuse. Let me know what you find.

Customer: replied 1 year ago.
Dear *****,
Since we never received a schematic for the unit (I assume you mean the unit under the house), how do we know how or where to find the circuit breakers for the inside unit, the on/off switch on the unit and the control board for a blown fuse?
Expert:  Tim H. replied 1 year ago.

I am talking about whatever it is that blows air through your house. This could be an air handler or a furnace depending on the part of the country you live in. If it's an air handler, it should be marked on the panel. There will also, usually, be a switch on the side. It may also have a drain safety switch which would cut the unit out if the drain was clogged.

Customer: replied 1 year ago.
Dear *****,
The air handler under the house is approximately the size of a twin bed. How would we know where to look?
Expert:  Tim H. replied 1 year ago.

Look for a thing that looks like a light switch. Is it on? Go to your main circuit breaker panel. Anything tripped?

Customer: replied 1 year ago.
As I stated in my original question, we have already checked the main circuit breaker panel for the house and nothing has tripped. As for the unit under the house, there is nothing that looks like a light switch. There are 2 switches that look like circuit breaker switches - one on top of the other. The top is marked 60 and it is on. The bottom is marked 30 and it is off. Again with the size of this air handler being "approximately" 2 feet by 2 feet, x 12 feet how can we know we are looking on the correct side. However, these 2 switches are attached to a floor joist about 20 inches from the air handler with wires running from the switches to the air handler. There are 2 heavy-duty "wires" that run to the 60 switch and no wires to the 30. How do we know we are looking in the right location?
Expert:  Tim H. replied 1 year ago.

I'm not sure why the 30 amp is off. Do you have electric heat with this unit? If not, that may be why this one is off. If you can get me make, and model I can try to pull up a wiring diagram on the unit. Look for the drainage system and see if it goes to a drain that has a couple wires coming from it. There may be a drain safety switch that has kicked power off because it is clogged.

Customer: replied 1 year ago.
Tim I have already furnished the make and model number of the unit twice now (feel free to check) but to re-iterate the system is a Carrier heat pump, serial number 25HCC548A300. The PRODUCT NUMBER IS:25HCC548A0030010. it does provide our heat also. WHERRE DO WE FIND THE drain system drain with the two wires running from it most We did ask for and pay for the most information etc
Expert:  Tim H. replied 1 year ago.

Since it is a heat pump, it also provides air conditioning. There has to be a way to drain water from the system. This is usually accomplished by means of 3/4 inch white PVC going away from the unit. If the system has a drain safety switch, and the drain is plugged, it will cut low voltage power to the thermostat. CLICK HERE FOR A PICTURE of a typical drain safety switch.

Expert:  Tim H. replied 1 year ago.

This is one possibility as to why your thermostat is blank. The other possibility is a blown fuse on the control board of the air handler. To access this, you will have to take the removeable panels off.

Expert:  Tim H. replied 1 year ago.

By the way, that model number you gave me is for your outside unit and this really doesn't help as it's your inside air handler that powers the stat.

Customer: replied 1 year ago.
In my INITIAL contact to "JustAnswer" at 8:57 pm eastern time on 09/01/15, and before I had my first reply from you, I gave you the brand of the system (Carrier) as well as the model number. At your request I sent you the information 2 more times, all of which I have copies of. It was not until your last reply at 10:10 pm that you say to me, "By the way, that model number you gave me is for your outside unit and this really doesn't help as it's your air handler that powers the stat." I don't understand why, when it was clear from your correspondence that the problem had to do with the air handler, that you would wait until 10:10 pm to advise me that the model number had to do with the outside unit, not the inside one. I would have been happy to crawl back under the house and get that number. Since I am where the AC unit is, I understand I have to provide you information, but I cannot do that without having you tell me what you need, as I have done in all our contacts. I'm sorry - it's nothing personal, but after spending over 2 hours online, I am not satisfied with the service received. I understand I am only to be charged $5, not the $45 that I would have paid for a solution. I would appreciate it if you would see to it that is all I am charged and you confirm this for me. I will be contacting American Express shortly to have them note my account that no further charges will be billed to JustAnswer. Thank you.
***** *****cc: JustAnswer
Expert:  Phil replied 1 year ago.

Hello, I understand that you do not wish to continue... that is no problem on my end. However it is apparent that there is either no power to the unit under the house, or a fuse on the printed circuit card in that unit has blown, or there is a bad 24 volt transformer in the outside unit.

If you wanted to check that you would go back under the house and remove the only two service panels on the accessible side of the unit. One of those will have a blower behind it, and there will be a printed circuit card mounted on the blower.

The wires that come from the thermostat will all end up there... check between the R terminal (red wire in most cases) and the C terminal...if you get no voltage read the transformer is bad or your homes main breaker panel that has a breaker in it marked AC or Furnace has tripped.

Look that over if you like, we can go from there.

Here are some pictures of typical printed circuit boards.

The unit under the house probably looks something like this.

service panel for the blower compartment is at one of the areas marked with a red square.

Stay in touch if you wish, we can go from there.

Please hold your rating if you choose to hang in with me until we get the problem solved.


Expert:  Phil replied 1 year ago.

If you would like to send me a few pictures of the unit under the house taken from about 10 feet away, and of the wiring diagram, and printed circuit board up close, well lit and well focused, I will mark those up with coaching instructions.

Expert:  Phil replied 1 year ago.

Use the paper clip icon at the top right end of the tool bar for that.

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