A/C not starting
#1
05-18-17, 03:13 PM
A/C not starting
I switched the thermostat over to A/C today, lowered the temp and it ran for about an hour. Since I was going to be out for a long time, I raised the thermostat temp to shut it off. When I came home I lowered the temp again and it will not run.
The thermostat clicks when the temp is lowered signaling that it works, but nothing happens. It has green, yellow, and red A/C connections.
I checked both breakers, they were on, but I cycled them off/on again just in case. I looked at the two pull out fuses outside and they are visually fine.
Looking for help in diagnosing the problem. My guess is that a fuse went (10+ years old), but don't know how to test them properly.
Help please!
Thanks guys.
The thermostat clicks when the temp is lowered signaling that it works, but nothing happens. It has green, yellow, and red A/C connections.
I checked both breakers, they were on, but I cycled them off/on again just in case. I looked at the two pull out fuses outside and they are visually fine.
Looking for help in diagnosing the problem. My guess is that a fuse went (10+ years old), but don't know how to test them properly.
Help please!
Thanks guys.
#2
05-18-17, 03:33 PM
Group Moderator
In order to check a fuse you need a meter set to ohms mode to check for continuity.
A voltmeter to measure for 240vac at the disconnect would be a good start too.
Use the same voltmeter and check for 24vac from R to Y and from R to G with the stat removed.
A voltmeter to measure for 240vac at the disconnect would be a good start too.
Use the same voltmeter and check for 24vac from R to Y and from R to G with the stat removed.
#3
05-18-17, 05:43 PM
Thanks Pete.
I was thinking there was more to testing the fuses than continuity... Anyway, the fuses passed. No voltage at the thermostat. It's dark outside so I'm not poking around the 240. My guess is, there is power at the fusebox.
If I'm right, how do I nail down what is wrong w/the air handler?
I was thinking there was more to testing the fuses than continuity... Anyway, the fuses passed. No voltage at the thermostat. It's dark outside so I'm not poking around the 240. My guess is, there is power at the fusebox.
If I'm right, how do I nail down what is wrong w/the air handler?
#4
05-18-17, 06:02 PM
Group Moderator
Since there's no power at the stat.... the problem is at the air handler.
You can check for a small fuse at the control board although a straight air handler doesn't usually have a control board. You may have lost the 24vac transformer.
You can post the model number for the air handler or remove the wiring access cover and post a picture or two. http://www.doityourself.com/forum/el...-pictures.html
A very typical problem is the contactor coil in the compressor shorts out taking the 24vac control transformer with it.
You can check for a small fuse at the control board although a straight air handler doesn't usually have a control board. You may have lost the 24vac transformer.
You can post the model number for the air handler or remove the wiring access cover and post a picture or two. http://www.doityourself.com/forum/el...-pictures.html
A very typical problem is the contactor coil in the compressor shorts out taking the 24vac control transformer with it.
#5
05-18-17, 06:30 PM
They are Carrier units, but model numbers will take some investigation...
What does the contactor coil in the compressor do? There is some added solenoid device that helps kickstart the compressor, installed when the unit was new.
What does the contactor coil in the compressor do? There is some added solenoid device that helps kickstart the compressor, installed when the unit was new.
#7
05-18-17, 08:03 PM
Group Moderator
Carrier/12AIRHANDLERS.pdf
The FB4B does contain an internal 5A protection fuse for the 24vac transformer.
The contactor gets its 24vac from the thermostat on a call for cooling and supplies power to the compressor.
There are two common things that cause that fuse to blow....
1) a shorted thermostat wire.... in particularly...... outside to the condensor
2) a shorted coil in the contactor.
The FB4B does contain an internal 5A protection fuse for the 24vac transformer.
The contactor gets its 24vac from the thermostat on a call for cooling and supplies power to the compressor.
There are two common things that cause that fuse to blow....
1) a shorted thermostat wire.... in particularly...... outside to the condensor
2) a shorted coil in the contactor.
#8
05-19-17, 04:10 AM
Thanks Pete.
Not my area of knowledge. Can you explain more about the contactor (where it is, what it does)? How do I test it?
When I looked at the thermostat wall plate when I first tried diagnosing the problem, the yellow wire was hanging off of the connection some so I adjusted it. Is that a potential short if it touched the red wire?
2) a shorted coil in the contactor.
When I looked at the thermostat wall plate when I first tried diagnosing the problem, the yellow wire was hanging off of the connection some so I adjusted it. Is that a potential short if it touched the red wire?
#9
05-19-17, 04:17 AM
Member
The contactor is a relay in the outside unit. When the thermostat calls for cooling, it sends 24VAC through wires to the outside unit. The 24VAC energizes the coil on the contactor, which pulls down a set of contacts to turn on the outside unit. To test the contactor, you would need to turn off the power to the outside unit, remove the two wires (24VAC) from the coil terminals, and take an ohmmeter and measure the resistance across the two coil terminals. There is no absolute resistance value for the coil, but it should be at least a few ohms. Also check resistance from either terminal to the mounting plate of the contactor. That should be infinite resistance (open circuit).
#10
05-19-17, 04:27 AM
Thanks Bob.
Looking around to see if I have a 5A fuse and then heading to the attic. After that, I'll check the contactor.
Looking around to see if I have a 5A fuse and then heading to the attic. After that, I'll check the contactor.
#11
05-19-17, 07:18 AM
It was the fuse. Thank you for all the help. I imagine the wire I adjusted on the thermostat plate was the cause.
Some new questions though:
There is a fair amount of mold in the air handler. I cleaned some, but how do you really eradicate it (especially since it's an ideal mold environment)?
The coil frame is very rusty and there is a little corrosion on the copper. It's 10-11 years old. How much does that matter? Does anyone make a SS air handler?
Approx. what does a replacement air handler go for these days?
Thanks guys!
Some new questions though:
There is a fair amount of mold in the air handler. I cleaned some, but how do you really eradicate it (especially since it's an ideal mold environment)?
The coil frame is very rusty and there is a little corrosion on the copper. It's 10-11 years old. How much does that matter? Does anyone make a SS air handler?
Approx. what does a replacement air handler go for these days?
Thanks guys!
#12
05-19-17, 10:37 AM
Group Moderator
Cleaning with a soap/bleach mixture will remove the mold. Allow the mixture to flow down the drain line to clean it too. Flush with clean water to remove the bleach smell.
New air handler.... around $1200-1500 installed. Depends on a lot of things... type of refrigerant, location, ease of access, size, etc.
Don't believe I've ever seen a stainless steel air handler.
New air handler.... around $1200-1500 installed. Depends on a lot of things... type of refrigerant, location, ease of access, size, etc.
Don't believe I've ever seen a stainless steel air handler.
