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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8052
Experience:  Furnace, A/C and heat pump specialist.
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I have a Trane XB1000 heat pump. On Monday night, my wife

Customer Question

I have a Trane XB1000 heat pump. On Monday night, my wife informed me that the upstairs unit in my house was not functioning and the temperature up there was 90 degrees. The downstairs unit was working fine. The air handling fan in the house was working fine. I examined the upstairs outside unit and the fan was not turning. The grill over the motor was very hot so I turned the upstairs unit off at the breaker box and let it cool off. I checked the capacitor with a Fluke 87V multimeter and it check out fine-5 microfarads for the fan side and 58 microfarads on the compressor side.(specs are 5/55 microfarads). I checked the contactor and it was working fine. After letting it cool off completely, I turned the power back on and the unit started up but the fan motor was making a worn bearing noise and the compressor appeared to be working fine. I removed the top grill and the motor and ordered a new motor which my wife will pick up tomorrow- diagnosis worn motor bearings.
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: yes the upstairs unit thermostat was working fine and the filters are clean. We continued to use the downstairs unit which did keep that zone of the house cool. However, today my wife informed me that that unit quit as well. When I got home, I checked the main breaker for that unit-OK. Had 240 V to the power side of the contractor but the relay was not working. However, it did work if I pushed in on the manual switch with a screwdriver- the fan came on normally, sounded good and the compressor seemed to be working fine. I thought it could be the relay so I swapped the relay from the upstairs unit to the downstairs unit and tried it again. Nothing. I of course checked to make sure the thermostat was set at 70 deg(ambient over 90 deg), on cool etc. I then jumped a wire from the yellow thermostat to relay wire on the upstairs unit to the downstairs unit, same with the blue wire and turned on the thermostat upstairs. The relay worked and the compressor and fine both worked. Of course, the upstairs fan went on but not the downstairs air handling fan. So it appears that it is a problem with the low voltage thermostat circuit- wiring, thermostat or a fuse for the low voltage system for the downstairs unit. My question is- how do I find the low voltage fuse for that unit and how do I test the thermostat?
JA: Do you plan on doing the work yourself?
Customer: Yes. I am quite capable in electronics.
JA: Anything else we should know to help you best?
Customer: I need to know where the low voltage fuse for the thermostat circuit is located so I can check it.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the HVAC Technician about your situation and then connect you two.
Submitted: 9 months ago.
Category: HVAC
Expert:  airheatman replied 9 months ago.

Let e make sure I understand everything.

1.Lookslike your upstairs fan is bad and you have ordered a motor.So that will correct that problem

2.Downstars contactor does not pull in by downstairs thermostat but it will from upstairs tstat with wires swapped.

Is this correct?

Customer: replied 9 months ago.
correct.
Expert:  airheatman replied 9 months ago.

Great Lets start by eliminating the thermostat. Reconnect the wires to proper outdoor units.Go to downstairs thermostat.Remove front cover. Loosen screws where wires connect to terminals and touch the R wire to the Y wire and tell me if contactors pull in and unit comes on.

Customer: replied 9 months ago.
It is a white rodgers thermostat and there are three wires going to the mercury switch- white, yellow and blue. On the AC unit yellow and blue go to the contractor. Should I jump yellow to white?
Expert:  airheatman replied 9 months ago.

What is model on the Tstat? Do you have a picture showing the wires?

If you have a paper clip icon on your page you can attach using that link.Or

You can upload the pictures using the tiny pic site .

Here is a link to the site.

http://tinypic.com/

Click on Browse , select the file from your folder.then click UPLOAD NOW.

They will give you a quote to enter in the box to verify you are a human.Enter the quote and click UPLOAD NOW

You will see your picture on right side of screen.

Then copy the link URL for email & IM

Paste that link here on the site.

Customer: replied 9 months ago.
it is type 1F56W-444, LR27935 Class 2 (###) ###-####
Expert:  airheatman replied 9 months ago.

Tell me if this is the right thermostat and if so what color wires are connect to what terminals

Customer: replied 9 months ago.
it is similar as far as the top goes- fan auto on and system cool off heat but that is where the similarity ends. There is some additional numbers on the sub base- 9737 E78
here is a picture:http://tinypic.com/r/v74o5v/9
Customer: replied 9 months ago.
I don't know if I did that right- my 17 yr old son helped me with that. Are you able to visualize the picture?
Expert:  airheatman replied 9 months ago.

Remove these screws to expose actual wires from furnace to thermostat

Customer: replied 9 months ago.
I have removed them
Expert:  airheatman replied 9 months ago.

what color wires are connect to what terminals

Customer: replied 9 months ago.
A small red wire comes thru back and goes to terminal RH. A thicker red wire jumps from terminal RH to RC. A small green wire comes thru the back and goes to terminal G. A small white wire comes thru the back and goes to terminal W. Two small yellow wires come thru the back to terminal Y.
Expert:  airheatman replied 9 months ago.

Excellent. Use a jumper or loosen screws and touch the red wire (Rh/RC)to the yellow wire (Y)and see if outside unit comes on.

Customer: replied 9 months ago.
I jumped the Red to yellow wires and nothing happened at the unit. However, it starts right up if I manually push in the relay.
Expert:  airheatman replied 9 months ago.

OK next jump R to G Red to green and tell me if indoor blower comes on

Customer: replied 9 months ago.
No the indoor blower did not come on
Expert:  airheatman replied 9 months ago.

OK go ahead and put thermostat back together.We have an electrical issue .Thermostat not getting 24v signal from furnace.Go to indoor unit and give me model on indoor furnace

Customer: replied 9 months ago.
Trane Model number TUE080A948K1 Serial Number M39531S1G
Expert:  airheatman replied 9 months ago.

OKI want you to open bottom blower panel and see if there if a small 3 or 5 amp fuse on furnace control board.If so remove it and see if it is blown.

http://i.imgur.com/pKP74Wg.png

http://i.imgur.com/kYe4Epz.png

Expert:  airheatman replied 9 months ago.

Board may look like this

Customer: replied 9 months ago.
Here is what I see inside the blower compartment. Should I remove the cover?http://tinypic.com/r/5vug5t/9
Expert:  airheatman replied 9 months ago.

Is this light on, off or flashing?

Expert:  airheatman replied 9 months ago.
Customer: replied 9 months ago.
OFF
Expert:  airheatman replied 9 months ago.

Ok if you will look at the chart on board that means we have no power to board.Push door button in and tell me if light comes on

Customer: replied 9 months ago.
it flashes red when I press the door switch in
Expert:  airheatman replied 9 months ago.

Ok lets look in the drain line and see if maybe there is a float switch that might be breaking circuit to thermostat.If so lift up on switch and call for ac and let e know if unit comes on.

Customer: replied 9 months ago.
I put the cover back on the blower to depress the switch and i moved the float switch up and down but the AC unit did not start.
Expert:  airheatman replied 9 months ago.

See if indoor fan will come on with float switch lifted

Customer: replied 9 months ago.
I was standing right next to the blower and did not hear any fan come on
Expert:  airheatman replied 9 months ago.

OK but thermostat is still calling for ac Yes?

Customer: replied 9 months ago.
good point. I had accidentally turned it off when I re-assembled it. Will try again.
Expert:  airheatman replied 9 months ago.

Standing by

Customer: replied 9 months ago.
No- does not come on with float switch in up or down position. The panel is flashing slowly with the door depressing the switch.
Expert:  airheatman replied 9 months ago.

OK somewhere we are losing the 24 volts from furnace to thermostat.May be a bad wire nut connection or something.Does that float switch wire into the red wire?If so might try bypassing it

Customer: replied 9 months ago.
the float switch interrupts the small red wire. I bypassed the switch but it did not come on. The wire nut connections appeared sound.
Expert:  airheatman replied 9 months ago.

Do you have a meter for checking voltage?WE are losing the 24 volts somewhere that tells thermostat to signal unit to come on

Customer: replied 9 months ago.
I mean neither the blower or the outside unit came on.
Customer: replied 9 months ago.
I have a very good Fluke Multimeter.
Expert:  airheatman replied 9 months ago.

You disconnect wires to float and twisted red wires together right?

Expert:  airheatman replied 9 months ago.

Lets check between R and C on furnace control terminal board where thermostat wires hook up (Door switch held in of course)

Customer: replied 9 months ago.
regarding the way I jumped the switch- i pulled off the wire nuts and used an alligator clipped wire to connect the ends of the red wire. However, the red wires were still connected to the float switch.
Expert:  airheatman replied 9 months ago.

OK just making sure.I have had people twist float switch wires together.Lets check 24v out of furnace at R and C

Customer: replied 9 months ago.
I have 27 Volts between R and C(checked on alternating current setting)
Expert:  airheatman replied 9 months ago.

OK now do this.Turn thermostat to call for AC or FAN and come back to furnace board and check between G and C for the 27 volts

Customer: replied 9 months ago.
With the thermostat calling for AC, door switch depressed, I only have 2.4 mv between G and C on alternating current setting.
Expert:  airheatman replied 9 months ago.

Go back to thermostat.Put the alligator jumper from R to G and check again

Customer: replied 9 months ago.
I removed the sub-base on thermostat and jumped from G to RH. Still 2.4 mV between G and C
Expert:  airheatman replied 9 months ago.

WE have a break in that red wire somewhere between furnace and thermostat

Customer: replied 9 months ago.
Going back several screens, I never did see that fuse that you told me to check.
So If I understand you correctly, If I jumped a wire between R at furnace and RH or RC on thermostat, the system would work. Is that correct?
Expert:  airheatman replied 9 months ago.

Yours does not have the fuse. We have verified we have 27v leaving the furnace.

Red goes to RH/RC at thermostat

Thermostat is basically just like a light switch

On call for fan R and G circuit close and send the 24v back to furnace

On call for AC RH/RC, Y and G all close and send circuit to furnace blower and outdoor contactor.

Jumping R to G at thermostat is bypassing thermostat and should close the circuit back to G

Somewhere between where the red leaves R at furnace we are losing it or in other words have a break in the wire before it gets to RH/RC at thermostat

Expert:  airheatman replied 9 months ago.

If you have a long piece of wire. Connect it to R at furnace and RC/RH .

Another thing you can try is put the alligator jumper directly from R to G on board and see if indoor fan come son

Customer: replied 9 months ago.
Jump R to G at the blower box?
Expert:  airheatman replied 9 months ago.

Yes and see if blower comes on

Customer: replied 9 months ago.
I jumped R to G at the board and the indoor fan came on
Expert:  airheatman replied 9 months ago.

That proves as I said, there is a break in that red wire before it gets to thermostat

Customer: replied 9 months ago.
I am going to run a long wire between R at the furnace and RC at the thermostat. Will that start the system?
Expert:  airheatman replied 9 months ago.

It should.I will stand by

Customer: replied 9 months ago.
OK
Expert:  airheatman replied 9 months ago.

Standing by

Customer: replied 9 months ago.
Ran out of wire. How do I get back with you maybe tomorrow night when I have some additional wire?
Expert:  airheatman replied 9 months ago.

Just sign in and go to MY Questions

Customer: replied 9 months ago.
Thanks will do
Expert:  airheatman replied 9 months ago.

Sounds good

Customer: replied 9 months ago.
Customer
Thanks for your very able help the other night. I am sheepish to tell you that I did not realize that the air handler and blower for the downstairs unit was in the crawl space and we were troubleshooting the downstairs low voltage control system using the upstairs furnace/blower which of course is not connected to the downstairs control system! At any rate, the problem turned out to be a faulty furnace service panel door switch on the crawl space furnace/blower unit which was jammed in the off position even with the door closed. The upstairs is now working fine since I replaced the motor and the downstairs is working fine since my HVAC friend bypassed the switch until I can get the replacement switch. Thank you so much for your help. I definitely learned a lot about the system with your help.
Bill
Expert:  airheatman replied 9 months ago.

If you have further questions, please let me know.

Thanks for letting me work with you.If my answer has been polite, professional,and thorough, please click one of the ratings before you go. If you still need help let me know!.Expert is not paid for assisting you until you rate answer.Feel free to follow up for 30 days at no additional cost. Bonus always appreciated if you feel justified.

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