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Jerry M.
Jerry M., HVAC Technician
Category: HVAC
Satisfied Customers: 153
Experience:  29 Years of experience in HVAC design -install- service -controls /Comm. & Residential
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after replacing broken capacitor, my Goodman AC still is not

turned on by the thermostate... Show More
turned on by the thermostate. The thermostate can turn on the furnace fan. Also, the fan and compressor of the AC unit both work when triggered by pressing the circuit connector in the panel.
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Jerry M. :

Greetings! I will do my best to assist you - thank you for posting your question on JUST ANSWER! Here are a couple of things to check: Take your electrical multi-meter and check for voltage across the two low voltage connections on the compressor contactor. Also, check from "Y" to "C" on the low voltage terminal board in your furnace, or "Y" to ground. Remember to keep the furnace door switch pushed in when checking for voltage at the terminal board.On most furnaces, if you have to remove the lower panel (blower compartment) there is a switch that kills the power to the furnace, and subsequently, the 24 volt supply (safety feature). If you do not have 24volts at the "Y" terminal when the thermostat is calling for the A/C to run, then the thermostat is bad. If you have 24volts at the compressor contactor, and it hasn't engaged, then the coil in the contactor is bad - please let me know back what you find - feel free to ask as many questions as you like! JERRY M.

Customer:

Jerry - thanks for getting back. I am not familiar with electricity; so need your help kind of step by step in order to follow your instrcutions completely. i do have a voltage meter. how do i identify the two low voltage connections on the compressor contactor? I saw "terminals" identified as L2, L1, and T2, T1. L2 and L1 connected by blue wires to the fuse box; whereas T2 connected by red wire and T1 connected by black wire to the compressor. Are any of these what you called as the low voltage connections? If so, how do I "check" for voltage?

Jerry M. :

To be safe, I would try testing at the furnace terminal board first - touch one of the test leads from your meter to the "Y" terminal and the other lead to "C", or to some bare metal on the furnace (ground). Before doing this test, make sure your thermostat is in "cooling" mode and the temperature setting is well below room temperature. One more thing - if you have to remove the lower panel on your furnace to access the low voltage terminals, be sure and hold the door switch in when you test for readings. If your furnace is also a GOODMAN brand, you may not have an actual terminal board - let me know back what you find - Jerry

Customer:

ok. i will start with testing of furnace. please confirm - put the thermostat switch at "cool", put the termperature setting low which actually kick off the fan. is it correct so far?

Jerry M. :

When you set the temperature below actual room temperature, the fan should start running (in cooling mode)

Jerry M. :

if it shuts off, there is something wrong with the controls

Customer:

i opened the panel of furnace (Carrier) and saw y and c. there are two wires (red and white) at y and one wire (yellow) at c. when to test, what setting should I set of the meter? and which probe touches which terminal?

Jerry M. :

One more question before you proceed, have any of these thermostat wires been unhooked/rehooked recently?

Customer:

no

Jerry M. :

Okay, thanks - it won't matter which lead you use on which terminal - you should be able to read 24 volts by touching "Y" and "C"

Customer:

the setting of meter - i have DCmA, DC V, AC V, OHM, and BAT. which should be set?

Jerry M. :

sorry - AC V

Customer:

i set at AC V 10 and tested as you instructed. the dial of meter went all the way from the left to the far right.

Jerry M. :

If you have a higher setting, try that

Customer:

50, 250, and 1000?

Jerry M. :

50

Customer:

i set at AC V 50. The dial went from the left to slight over the middle of the scale.

Jerry M. :

Okay, it sounds like you are getting the necessary voltage at the "Y" terminal - here is the next step that will enable you to solve the problem give me a few minutes to type

Customer:

i mis-stated one thing about the wires to y and c. wires connected to y are yellow and white (not red and white). wire connected to c is red, not yellow.

Jerry M. :

Take note of the wire/wires that are connected to the "Y" terminal and the wire/wires that are connected to the "C" terminal. These wires will exit the furnace cabinet together in what looks like a thermostat wire. Most likely they will be fastened to the refrigeration lines that run between the indoor cooling coil and your outdoor unit (condenser). You will have to remove the cover from the electrical compartment on your outdoor unit so you can find these wires and their connecting points on the compressor contactor that was mentioned earlier. BEFORE you remove the electrical cover on the outdoor unit, turn off the circuit breaker that supplies the 240 volts to it. Be safe! When you find these "thermostat" wires in the outdoor unit, verify they are the same color as the ones hooked to Y and C in the furnace. Also, stick your electrical test leads on these wires where they connect to the contactor and see if you can read 24 volts BE SURE the 240 volt power supply is OFF! for your safety. You should still have 24 volts at the contactor even with the air conditioners circuit breaker turned off. The low voltage circuit is powered from the furnace

Jerry M. :

You will be looking for a red and a white wire in the outdoor unit electrical compartment, as per your update

Customer:

yellow wire from Y goes out of furnace cabinet together with a few other wires in one wrap. Red from C and white from Y go together in one wrap without other wires. is this expected? I am not sure where each of the two "wraps" coming out from furnace goes. what is my next step? does the wire I will be looking for go into the outdoor unit?

Jerry M. :

Yes, what you are seeing is typical - you want to follow the wrap with just the the red and white wires - it will enter the outdoor unit very close to where the main 240 volt power supply goes in Note: The other "wrap" with more wires is going to your thermostat in the house - just fyi

Customer:

ok, i saw the red/white wires coming from house into outdoor condensor unite. each of the two wires is connected with other wires within the unit. I removed the caps at the wire connection and test the voltage with setting at AC V50. One probe to one wire at the same time. the dial did not move.

Jerry M. :

after you removed the caps, did all wires remain fastened together as you tested?

Customer:

yes

Jerry M. :

there appeared to be no voltage present, correct?

Customer:

it looks that way.

Jerry M. :

Another question, did the two wires that were connected to the red and white wires go directly to the contactor, or did one of them go to a small circuit board or some other electrical-looking device?

Customer:

the white wire connected to another wire which goes to a timer type of device by ICM. the red wire connect to a board type with wires connected to fuse and compressor.

Customer:

i should have said teh red wire connected to a wire which goes to a board type of device with wires connected to fuse and compressor. by the way, I was not sure what you meant by contactor.

Jerry M. :

Okay, the ICM device is a time delay, which keeps your compressor from starting immediately upon a call for cooling from your thermostat. This is used as a protective measure for your compressor so it cannot be cycled on-and-off (bang-bang) if someone is "playing" with the thermostat setting. The time delay typically ranges from 3 - 5 minutes. Your ICM unit may have a small knob on it that allows it to be adjustable. If your compressor does not start after, say 7 minutes, then the ICM time delay is defective and needs replaced.

Customer:

for my understanding, is the meter reading supposed to show no voltage when I test the red/white connections inside the outdoor unit?

Customer:

so, if I let the furnace to run for 5-7 minutes, the compressor should kick in if everything is normal? otherwise, the timer is faulty?

Customer:

i just looked, the timer's knob is set at 3 minutes.

Jerry M. :

Yes, if every thing is normal - back to your earlier post: Good point! My mind skipped over that fact that you previously stated! Yes, you should have been able to read 24 volts at the wire connecting caps, since this was before the time delay device. If 24 volts are not present, this indicates that your wiring has been damaged between the furnace and your outdoor unit. This would typically be caused by a mouse or some rodent chewing on it, or I have also had a customer whose dog chewed on it outdoors. Sometimes the wire can rub against something long enough to wear or "cut" it in two - these are things to look for. I saw your last post while I was typing - 3 minutes - if EVERYTHING is normal, compressor should start approx. 3 minutes after furnace comes on

Customer:

so you ruled out the possibility of timer problem for now? How do I look for problems in the wires between furnace and the outdoor unit?

Customer:

one thing should be noted is that the AC worked fine until the capacitor broke (last year). I replaced the capacitor today. if the wires indeed were damanged, it would have been between then and now. Or, could the power of capacitor's implosive break damage the wires?

Jerry M. :

Let me ask you this: Have you allowed ample time( 3 minutes or more) for the compressor and outdoor fan to come on, assuming everything is normal?

Customer:

not i can remember. i replaced the capacitor. turn on thermostat. maybe after 1 minute of no response, I shut the thermostat.

Jerry M. :

I have been reviewing our chat - with no voltage present at the wire connections outdoors, but 24 volts at Y and C at the furnace, I have to say that it appears your problem is in the wiring between the furnace and outdoor unit

Customer:

how do I fix this?

Jerry M. :

Rather than investing a lot of time inspecting/testing the existing wire, I recommend that you measure how much(length) wire it will take to replace it, and go to your local hardware store and purchase ___ ft. of 18/2 thermostat wire and then replace the old wire. PLEASE CONSIDER suggestion #2: Call an experienced hvac technician to come check your unit. A good tech should be able to pinpoint your problem in very short order, and have the wire or whatever else is needed already with him. In the big picture, this may be the most satisfying for you!

Customer:

ok. thank you for taking me through these steps. I will replace the wire. If it still does not fix the problem, at least it will rule out the wires as a possible cause.

Jerry M. :

Let me know how it all turns out - best wishes to you!

Customer:

after i replace the wire, if it does not fix the problem, could I have your guidance again tomorrow?

Jerry M. :

Certainly - I will check back tomorrow for a new post from you! It will be around noon central time, before I will be able to check back - hope that works for you

Customer:

great. good night!

Jerry M. :

Good night

Customer:

Jerry - After one night sleep, my head gets clearer this morning. The reason that I could not read voltage of the red/white wires in the outside unit was I did not place back the furnace panel. Once i corrected what I did wrong last night, I was able to read the voltage. Then, as you instructed yesterday, there is a time delay for the outdoor unit to kick in. The AC is functioning now. Thank you for your instructions and advice.

Jerry M. :

Hey! - that is good news! Way to go - I have experienced exactly the same - new day/ clearer thoughts! Thanks again for using Just Answer and best wishes to you! Jerry