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Scottyp · Sep 29, 2008, 07:15 AM

Installed a new Honeywell Programmable Thermostat RTH7500 for heat pump energy savings. Replaced an old York thermostat "York T874R 1046" with a Honeywell subbase Q674L 1272. After the installed the system worked well with the new thermostat for a few days. Then, I noticed the fan would not shutoff. The fan runs with all settings: System on/off, termostat on/off, and when thermostat is removed from subbase. All connections are solid and no wires are touching.

My York Air Handler has emergency electrical heat and located in the attic. I do not have an electrical schematic for the unit and a drawing is not mounted inside of the door panel. I think the Air Handler Model is 2HL06501506C (maybe the Coil Model number). Inspected the wiring from the thermostat: all connected, none touching, no visiable problems.

Im not very AC knowledgeable but not a novice and very comfortable working on the unit and its circuits.

Any ideas of the cause and test that I can perform.

Scottyp · Sep 29, 2008, 09:13 AM

Update:
Thermostat: York/Honeywell T874R1046, sub-base Q674L 1272
Furnace: York Electric.
Air handling section: N2AHD14A06
Heater section: 2HL06501506C

Where can I find an Electrical Diagram for the York Air Handler unit?

hvac1000 · Sep 29, 2008, 01:59 PM

Look on the inside of the blower door.

Scottyp · Sep 29, 2008, 04:28 PM

Where is the relay or sequencer?

Here's a picture of my wiring inside the furnice:

Here's the inside of the cabinet pictures:

Where is the relay or sequencer?

Scottyp · Sep 30, 2008, 09:53 AM

Thanks, I found the diagram inside of the circuit cabinet door.

I just need a little help here please...
Where is the relay & sequencer?
How do you test them?

hvac1000 · Sep 30, 2008, 10:12 AM

Second pic sequencer is on right side. Test to see if M1 and M2 are closed. IE remove power and wires and test across terminals. (REMEMBER WHERE THE WIRES WERE)If they are closed then the sequencer is calling for the motor to be on at all times and it is defective. OR easier test is to just remove wires off M1 (TAPE THEM TO PREVENT SHORT)and energize the unit. If the motor has stopped running the sequencer is locked on and is defective.

Scottyp · Sep 30, 2008, 10:45 AM

Thanks for a response hvac1000.

In the second picture, how many sequencers are present? Only one has the M1 & M2 stamp.

Also in the second picture on bottom left, is a white box. It has what appears to be a switch on the other side. The switch is frozen on one side and will not toggle/reset. What is it?

EPMiller · Sep 30, 2008, 05:21 PM

Originally Posted by Scottyp

Thanks for a response hvac1000.

In the second picture, how many sequencers are present? Only one has the M1 & M2 stamp.

Also in the second picture on bottom left, is a white box. It has what appears to be a switch on the other side. The switch is frozen on one side and will not toggle/reset. What is it?

There are 2 sequencers in that picture. Usually those control the electric resistance heat. There usually is another relay somewhere that controls the fan. Your picture is fuzzy, but I wonder if that bakelite brown piece to the left of the sequencers isn't the relay you want. Trace the wiring back from the fan and see if it goes to that piece. If it is, just pull the fan wire off the terminal, turn the power back on (you did kill the juice first, right?) and see if your fan isn't off. If it is, you found your relay. Next reconnect that terminal and pull one of the relay coil leads off. If your fan is still on then replace the relay. Unless something else is in parallel with it, like an overheat limit switch or the like, then you have to isolate the problem to the particular part. You have to use the schematic if you really want to troubleshoot things.

That white box looks to me (again fuzzy) like a circuit breaker. Those toggles don't move unless they are tripped.

EPM

hvac1000 · Sep 30, 2008, 06:40 PM

M1=motor one
M2=motor two.

Underwriters Laboratories requires a

fan interlock circuit to insure the blower
remains operating whenever more than one
sequencer is used. The fan interlock should

be the M contacts of the second or third sequencer.

All M contacts are wired to the blower motor

so that any sequencer that is energized at will operate blower

http://www.white-rodgers.com/wrdhom/.../0037-4799.pdf

http://www.white-rodgers.com/wrdhom/..._06_pg0096.pdf

Some units have relays and some just use the sequencers

Scottyp · Oct 1, 2008, 02:07 PM

Originally Posted by hvac1000

OR easier test is to just remove wires off M1 (TAPE THEM TO PREVENT SHORT)and energize the unit. If the motor has stopped running the sequencer is locked on and is defective.

Did the Easier Test. Removed & taped both wires off M1 and turned on the unit.
Results: Fan came on...

Originally Posted by EPMiller

Your picture is fuzzy, but I wonder if that bakelite brown piece to the left of the sequencers isn't the relay you want. Trace the wiring back from the fan and see if it goes to that piece. If it is, just pull the fan wire off the terminal, turn the power back on (you did kill the juice first, right?) and see if your fan isn't off.

The bakelite brown piece is a relay. I traced a wire back to the fan and disconnected it...
Results: Fan came on...

Originally Posted by EPMiller

If it is, you found your relay. Next reconnect that terminal and pull one of the relay coil leads off. If your fan is still on then replace the relay. Unless something else is in parallel with it, like an overheat limit switch or the like, then you have to isolate the problem to the particular part. You have to use the schematic if you really want to troubleshoot things.

Pulled one of the relay coil leads..
Results: No fans but constant hummmm...

Tested for 24volts on the green wire from thermostat with power on/fan running. Nothing...

EPMiller · Oct 1, 2008, 05:45 PM

Originally Posted by Scottyp

<snip>
The bakelite brown piece is a relay. I traced a wire back to the fan and disconnected it...
Results: Fan came on....
Pulled one of the relay coil leads..
Results: No fans but constant hummmm...

Tested for 24volts on the green wire from thermostat with power on/fan running. Nothing...

I'll admit, troubleshooting by email is a lot harder than hands on.

When you pulled the fan relay coil lead possibly you heard a hum that is always there, just masked by the fan noise. If the fan quit when that lead was pulled, something is energizing the fan relay. I don't know how you tested for 24 volts, but measuring from green to red at the tstat would show 0vac when the fan is being called. That's equivalent to measuring from hot to hot. Green to the C terminal should be 24vac with the fan being called. It appears by your pictures that you do not have an integrated control board so you should be able to trace where that signal is coming from. Turn the tsat so that it is NOT calling for cool (or heat), turn the fan switch to auto, wait for two minutes or so (fan overrun time SHOULD be finished) and then, if the fan is still running, check for voltage between red and green at the tstat. If you still have nothing (0vac) then something is likely wrong with the tstat. Disconnect the green at the tstat, if fan stays running then something is wrong in the wiring.

I REALLY need that schematic.

EPM

Scottyp · Oct 1, 2008, 07:28 PM

Here's the Schematic:

Scottyp · Oct 1, 2008, 07:38 PM

Originally Posted by EPMiller

I'll admit, troubleshooting by email is a lot harder than hands on.

When you pulled the fan relay coil lead possibly you heard a hum that is always there, just masked by the fan noise. If the fan quit when that lead was pulled, something is energizing the fan relay. I don't know how you tested for 24 volts, but measuring from green to red at the tstat would show 0vac when the fan is being called. That's equivalent to measuring from hot to hot. Green to the C terminal should be 24vac with the fan being called. It appears by your pictures that you do not have an integrated control board so you should be able to trace where that signal is coming from. Turn the tsat so that it is NOT calling for cool (or heat), turn the fan switch to auto, wait for two minutes or so (fan overrun time SHOULD be finished) and then, if the fan is still running, check for voltage between red and green at the tstat. If you still have nothing (0vac) then something is likely wrong with the tstat. Disconnect the green at the tstat, if fan stays running then something is wrong in the wiring.

I REALLY need that schematic.

EPM

Agreed... Hands on is a lot better.. But now, I only have a humm... :(
Fan has stopped running.. :mad:

Tested for 24 volts from Green to C and thermostat turned off (fan auto). Result 0 volts
Maybe the relay completely died when testing... Hopefully... :confused:

MarkwithaK · Oct 1, 2008, 07:42 PM

With your stat off, FAN set on Auto you won't have voltage from G (Fan) to C (Common). Set the Fan to ON and you SHOULD have 24 volts.

Scottyp · Oct 1, 2008, 08:02 PM

Agreed.. The problem is that I have a fan running continuously with 0 volts on Green (fan) wire... And I don't want it to stay on with the AUTO setting... It SHOULD go off with heat/ac quits..

hvac1000 · Oct 1, 2008, 10:40 PM

Look at 2R (Relay for blower motor) on your wiring diagram (lower right side). If this relay is defective (shorted closed) it will keep the blower running all the time no mater what you disconnect except the main power. Check 2R I have a feeling your problem might be located there.

MarkwithaK · Oct 2, 2008, 06:08 PM

Some times these relays can stick. You may be able to tap on it to free it up.

Scottyp · Oct 2, 2008, 06:31 PM

Tapping on the Relay didn't work.. I think it made it worse.. :(
I went from fan ON always to humming always... :mad:

Tried to find a replacement blower relay today and can't find one locally. The York (024-24984-000) relay is a 5-pin relay and all of the stores has 6-pin relays. Im being told that it's a (special order only) York part. Im searching online for alternatives..

Relay Manufactured by: ESSEX
Essex Part number: 134-20103-301Q
York Part number: 024-24984-000
12FLA 60LRA 125VAC
8FLA 48LRA 250VAC
18A 277VAC
COIL 24V 50/60Hz

Anyone knows of an equivalent relay that I can use?
What's a good online site for HVAC parts?

hvac1000 · Oct 2, 2008, 07:03 PM

That is just a single pole single throw/single pole normally open relay. Known as SPST/SPNO relay with a 24 volt coil.

SEE actual page 115 on below info and tell me if it looks something like the relay pictured.

http://www.white-rodgers.com/wrdhom/...ers_relays.pdf

If so you will need a 90-370 5 tab unless York had it modified for there usage. BTW you can use a 5 or 6 tab relay. Just follow the wiring diagrams listed on the Whire Rodgers relay page. You just have to used the same numbers for the connections you need. QUESTION?? Is this relay on a circuit board or freestanding?

Do not worry about the last 000 in the York part number. This site has it but it is expensive there.

http://bestbuyheatingandaircondition...ory_Code=r-rbm

Cheaper here at Grainger

http://www.grainger.com/Grainger/wwg...=19&submit.y=1

ALSO I would suggest you look on the side of the relay for a wiring diagram and make sure you get the correct one. It will make life easier for you as far as wiring goes. Grainger stocks all these type of relays.

Here is the list page

http://www.grainger.com/Grainger/wwg...e&CatPage=3827

Scottyp · Oct 3, 2008, 08:13 AM

The really at bestbuy Heating & Air Conditioning is the exact match to my relay.
I do not have a circuit board and the blower relay is freestanding.
Its just to the left of the sequencers in the 2nd picture.

Relay wiring diagram:
- Pins 1 & 3 coil
- Pins 4-to-5 in default state
- Pins 4-to-2 in the activated/triggered state

Thanks for the info hvac1000! :)