AC compressor not turning on with thermostat

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Old 05-28-14, 09:15 PM
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AC compressor not turning on with thermostat

I have a honeywell 6450 thermostat, rheem criterion ii plus gas furnace and a rheem classic ac unit. I tried to start up the air conditioner for the season by turning on cooling on the thermostat. The furnace blower motor turned on and runs constantly. The ac compressor does not turn on. When I turn the heat on the furnace fires up fine. I replaced the thermostat today to eliminate that possibility. There are 4 wires running to the thermostat. 1 red wire I connected to red jumper spot, 1 white which I connected to white, 1 green which I connected to green and 1 blue which I connected to y. These designations match up to main control board at furnace. I have a fluke meter and would like help on trying to take voltage readings to try and determine why the compressor is not kicking in. Anybody willing to share some diagnostic steps? Thank you in advance.
 
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Old 05-28-14, 09:21 PM
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Welcome to the forums.

Have you checked your AC supply to the compressor unit. Reset the supply breaker ?

You have four wires from the stat to the furnace. Then you should have two wires from the furnace to the compressor unit.

Go out to compressor unit and locate where that two wire cable enters. Check at that location for 24vac. We need to determine if the problem is a switching problem or a compressor problem.

An A/C system low on refrigerant charge will not run.
 
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Old 05-28-14, 09:30 PM
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I also sub blue for yellow when yellow isn't available.
R = power
Y = compressor
W = heat
G = fan

http://i151.photobucket.com/albums/s...ps82569ce0.jpg

Are you getting 24 volts to the outdoor unit field connections?
http://i151.photobucket.com/albums/s...ctricPanel.jpg



If you do not have 24 volts outside, check inside for a full drain pan and a tripped float switch.
http://i151.photobucket.com/albums/s...n204/PTrap.jpg


Is the outdoor unit contactor pulled in?
Do you have 240 volts at L1 to L2?
What About T1 to T2 ? (outlet side of contactor)
http://i151.photobucket.com/albums/s.../Contactor.jpg

If the contactor is pulled in bu the condenser isn't running is the run capacitor swollen on top?
http://i151.photobucket.com/albums/s...Baddualcap.jpg
 
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Old 05-28-14, 09:39 PM
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Thanks for the quick reply. I did measure the voltage and it has a bit over 20vac. I did also take voltage on the 240 line coming in at the compressor and that checks out at 240vac. So does that mean that i am low on freon? If so what is the correct charge value for high side and low side readings? I am unsure of what you mean when you say resetting the supply breaker? Does that mean breaker at the main electrical panel? Thanks again for your help.
 
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Old 05-28-14, 09:45 PM
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http://www.doityourself.com/forum/ai...ng-your-c.html

Charging instructions are not allowed on this site.

20 volts is low.

Do you have 20 volts at the contactor low voltage connection or only the wire nuts entering the condenser?
 
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Old 05-28-14, 09:45 PM
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I do not get voltage on the t1 and t2 side.
 
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Old 05-28-14, 09:50 PM
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The voltage reading was taken at the wire connection
 
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Old 05-28-14, 10:18 PM
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Check for 24vac on the contactor. Usually the smaller wires on the sides of the contactor.

L1 and L2 are 240vac in
T1 and T2are 240vac to compressor when contactor closes.
 
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Old 05-29-14, 11:16 AM
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Just an update on a few things. I checked the voltage on the contractor this morning and there was zero volts. I then went back into the wiring splice before the contractor where the energy savers device is normally installed and got zero volts again. Last night when I got 20v ac I remember I was wiggling the wire a bit as the volts initially were really low in the low single digits. So my thought this morning was that there was a break in the red it white wire going out to the compressor and proceeded to replace this wire. I replaced the wire and still no power at the contactor. Just now I took voltage readings at the main control board at the furnace with my thermostat set to cooling. The only combination that had some voltage was c and w. And that read about 15 vac. I am wondering if I need to test the 24 volt transformer now. I read on another thread that if the system doesn't get 24 volts then the fan will run all the time on some systems. This is he case for me currently as nothing shy of shutting off power will turn off the fan. One other general question. Will the furnance main board automatically be grounded or would there be a wire running to the c connection besides the ground used for the compressor? I imagine so but wanted to check. I'm guessing next step is to check the transformer. Any help on doing that would be appreciated.
 
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Old 05-29-14, 11:21 AM
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Can you elaborate on this "energy saver device" ?
 
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Old 05-29-14, 11:24 AM
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Also...if you have a green light on your board with the safety switch pressed in at the blower door, there is nothing wrong with the transformer.
 
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Old 05-29-14, 01:31 PM
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I do have 2 out of the 3 green lights lit on the control board when the blower door safety switch is pressed in. Energy saver switch is installed by the electric company and is described as a switch that automatically cycles your ac on and off for brief intervals when their is a high demand for electricity during the summer. It is a device that simply is between the power feed going to he air compressor where I am guessing they can remotely interrupt the power.

Any other ideas? Perhaps try to jumper red lead at control board to y for air compressor and see if that possibly works? Still doesn't make sense I don't show any voltage when probing r and c though as I thought that should be all the time hot.

Here is a pic of the control board lit up.
 
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Old 05-29-14, 03:48 PM
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There should always be 24vac from R to C.
When in A/C mode there should be 24vac from Y to C. There should be 0v between W and C.

Can you give a nice clear shot of the board ?
What is the model number of the furnace ?
 
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Old 05-29-14, 06:26 PM
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Hopefully these pictures will work. Model of furnace is RGPK-10EAMER. I have one picture of the board and the second picture showing the test results of zero vac between r and c. From the looks of it line voltage comes into the board and then travels through the transformer to step down to 24vac. After it comes out of transformer there is an inline fuse which I checked for continuity and that checked out fine. Let me know if there is anything else I might be able to provide. I truly appreciate all the help so far. It is a rheem criterion ii furnace.
 
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Old 05-31-14, 09:57 AM
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Just an update to possibly spur any additional ideas. I replaces thermostat wiring to the thermostat and also replaced the transformer. I now verified there is 24vac coming out of transformer and going into the board. Still when I take a voltage reading at the thermostat screws on the board I only get random readings from 15vac down to about 5vac when probing the red and common terminal. To rule out wiring issues or bad thermostat even though they were just replaced I took off all the wires connecting to the furnace control board thermostat screws. It seems to me this is telling me it's a bad board. If 24vac is verified going into the board and there is not this going out seems like that is only option? Or possibly could there be a bad ground where I could manually wire a good ground to the c terminal to create this? Or what normally breaks on these boards?
 
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Old 06-01-14, 10:56 AM
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Took off the board today and found trace bad on the common wire.
 
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Old 06-01-14, 11:01 AM
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That would be enough proof for me to condemn the board.
 
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Old 06-01-14, 11:47 AM
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Can you make a solder repair of the board ?

The C - Common screw terminal on the board is connected to one of the 24 VAC out wires of the transformer . The other is connected to the R - Red .

Also try to determine which of those 2 24 VAC wires is the C . Wire nut in a jumper wire with the C - 24 VAC wire from the transformer . Run the other end of the jumper wire to the C - screw on the terminals of the board .

Now put everything back together , except , remove the 2 wires going to the condenser unit , from the terminal board .

Turn on 120 VAC . Check if you have 24 VAC from R - Red & C - Common . If so , good so far .

Now , something caused the trace on the control board to burn out ? From what I remember of your description , the only thing , external to the furnace , connected to the C- Common terminal is the wiring going to the condenser unit ?

Disconnect the 2 24VAC wires at the condenser unit .

Does the power company device tie in to the 24 VAC or the 240 VAC ? I am wondering if it contributed to the burn out trace on the control board ?

With nothing connected to either end of the 2 wires from the furnace to the condenser unit , put your meter on ohms or continuity . Se of there is a short between those wires . Then test each wire to earth ground ( you should be able to use the copper refrigerant lines as an earth ground , if you can not find another ) .

If no short , connect the two 24 VAC wires , at the furnace , to the C- Common and Y - Yellow . With the Tstat on cool , test the condenser end of those wires & see if you are getting 24 VAC or slightly more ?

If you are , I would carefully ( with power off ) connect those 2 wires to the control wiring of the condenser unit . If they previously wired through the power company device , I would by pass it , for the time being .

Now , with the 240 VAC at the condenser unit still off , have some one inside the house turn the tstat on & to cool . See if the contactor , inside the condenser unit clicks / pulls in ?

If so , turn the tstat off again , restore the 240 VAC to the condenser unit . Have the 2nd person turn the tstat back on & to cool . What , if anything does the condenser unit do now ?

God bless
Wyr
 
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Old 06-02-14, 06:30 PM
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Thanks Wyr! I appreciate the additional diagnostic advice/steps. I put in a new control board and can proudly say I have AC. Before putting in the board i did take your advice on verifying no shorts in the wires. I love learning about how things work and thanks to everyone for sharing their knowledge.
 
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Old 06-02-14, 07:17 PM
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You can't always immediately see or find shorted wiring. In other words.... it could happen again. If the board doesn't have a 3A fuse protecting it or an inline fuse to the transformer...... one should be installed. In your one picture I see a yellow miniature glass fuseholder. If that's for the transformer.... make sure it has a 3A (4A max) fuse.
 
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