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I have a seven year old Honeywell Chronotherm IV Plus that

has worked flawlessly until the...
I have a seven year old Honeywell Chronotherm IV Plus that has worked flawlessly until the last several months. The 5 amp fuse in our heat pump control panel blew four months ago. I changed it and everything worked fine. One month ago, my wife switched the thermostat from cool to heat and it immediately blew the 5 amp fuse again. I changed it and everything was fine. Today, we awoke and found the fuse blown again. It was a cool evening and I would easily guess that the thermostat called for heat. We found the fuse blown again. Does this sound like the solid state controls of the Honeywell thermostat are going and a new one is needed. Thanks John Cignatta at XXX-XXX-XXXX
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Answered in 1 minute by:
10/2/2011
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8,516
Experience: Furnace, A/C and heat pump specialist.
Verified

airheatman :

Coild be a short in control wire

airheatman :

First I would like to inquire as to whether it blows the fuse everytime it is turned to heat or goes into heat mode.It could be a short in a control wire or in a

airheatman :

If it doenst blow immediately upon going into heat mode, I would suspect possibly a short in the sequencer or wires to sequencer.Problem with a shrt is that it can be time consuming to locate brcause it can be in the thermostat,air handler ,outdoor unit or control wiring in between

airheatman :

To eliminate the thermostat from being the culprit, you can disconnect wires from thermostat and twist appropriate wires together for each mode and see if fuse blows while thermostat is bypassed,This can be a bit time consuming,but really the only way to say thermostat is bad or not .If it sounds like a porject you want to attack, I will guide you through the process,just let me know

Customer:

We replaced the fuse and the thermostat powered up. After a minute, it called for heat and immediately went blank. Thus, it appears that it blows the fuse whenever it calls for heat. What should I check first?

airheatman :

re youcomfortable removing thermostat cover ad remving the wires from terminals

Customer:

Absolutely.

airheatman :

OK.First turn the breaker off to the air handler.remove each wire,( markthem or write down what color comes from each terminal for easy replacement when we're done

airheatman :

I am going to need you to tell me the number and color of every wire used and where you take it loose from(unfortunately controlwire comes in different variations and techs use different colors for different things)

Customer:

OK. They are all disconnected. The connections in use on Honeywell Thermostat on the bottom row are R-red, W2-white, E-black, W1-yellow, Q/B-orange, G-green, and C on the top row-blue.

airheatman :

Great, now make sre the wires are spread apart so they cannot touch each other and turn power back on

airheatman :

thrn let me kow you are ready

Customer:

Put new fuse in AHU control panel and it did not blow when two AHU CB's turned back on. All wires are apart. I have my multimeter ready for checking line voltages or continuity.

airheatman :

Do you have a few uses?

airheatman :

fuses

Customer:

Still have three left.

airheatman :

First I want you to twist,jumper or hold the RED and ORAGE together.Ts should bring the het pump on in heat mode

Customer:

I will do that in a second. I just checked voltages between each lead and the green ground wire. All voltages between each wire and green are 7 volts DC except for red. It is at 11 volts. Do you want me to go put a jumper across red and orange?

airheatman :

Yes please

Customer:

It has been several minutes since jumping red and orange. The HVAC has yet to cycle ON. The Trane control panel is still powered and the fuse has not blown. LEDs are cycling. What next?

airheatman :

OK, nothing shorted good

airheatman :

Let me ask you a question Did you remove a wire from Y at thermostat? I dont see it listed

airheatman :

We should have a Y, that is for the conatctor in outdoor unti

Customer:

Y1 did not have any wire attached to it or shorted to it with a jumper. The yellow wire from 7 conductor cable was connected to W1. Then I go down to the control panel and I see that the yellow wire (from W1) connects to the bus marked "Y".

airheatman :

Has thermostat wiring been messed with prir to our converstaion today?

airheatman :

This may be your problem is mis wired.Let me know when you are ready to contiue our tests

Customer:

No. I moved it off the wall to paint behind it maybe four years ago and I did not disconnect any of the wires. No one has touched it but me. No service calls or repairs since it was installed.

airheatman :

ok lets contine

airheatman :

ok

airheatman :

continue

Customer:

Ready to go.

airheatman :

OK add Y to the juncton of RED and ORANGE so you will now have RED<ORANGE and YELLOW all tied together

Customer:

Compressor outside just came on. I hear the sound of fluid going through the fan coil in the AHU. Still have not had fan start for AHU. Let me go check and see if there is a door switch on the AHU.

airheatman :

Fuse did not blow right?

Customer:

Correct. Fuse is good. Compressor is running. LEDs flashing on AHU control panel and red, orange and yellow thermostat wires all shorted together. Also, I closed door to the AHU and no effect. (I did not see a door switch anyway.)

airheatman :

Ok add green to the mix. RE/YELLOW?ORANGE?GREEN

airheatman :

RED/GREEN/YELLOW/ORANGE

Customer:

It took a minute and the AHU kicked on. The register feels a little warm. Need another minute or so to confirm that it is heating house. Fuse did not blow.

airheatman :

Red is power wire,yellow brings in contactors outside,orange controls reversing valve and gree controls blower. with those together, blower should run,outdoor ynit should be on and the large copper line coming to the aor handler should be very warm

Customer:

What next?

airheatman :

Fuse not blown right?

Customer:

Correct. Fuse is good.

airheatman :

Great. np carefully disconncet the wires and seperate them agaion

Customer:

Done and AHU just stopped.

airheatman :

ok, now i want you to connect the RED and WHITE together

airheatman :

White contols your indoor heating elements.The blower should come on and the elements in the air handler.air shoul be warm at registers,might even smell a little dut burning if they havent been on in awhile

airheatman :

dus

airheatman :

dust not dus

Customer:

I checked fuse first and it was good. Then I jumpered white and red. Went donw to AHU and the fuse is blown.

airheatman :

Ok then you have ot a short in the white wire somewhere or one of the haet sequencers is shorted

airheatman :

turn power off

Customer:

Power is off.

airheatman :

Look where the white wire is coming int the air handler and trace where it goes to in the a/h

airheatman :

Trane i very secretive with their manuals in an effort to allow exclusive Trane Dealers to be able to chargewhat they want ,therefore I am unabale to google a wiring diagram to look for you

airheatman :

Locate the first connection in the air handler whre the white wire from thermostat connects.If it is on a control board, then there will be a white out of control board going up to elements or a limit

Customer:

I found where the white wire was in the seven wire bundle and it passed thru a good grommet in side of AHU. The bus where the white wire connected was checked against the side of the steel cabinet of the AHU and the terminal was shorted. I disconnected the white wire and left the jumper in place on the terminal board and re-tightened it. The terminal board was no longer shorted to the cabinet. The white wire which is disconnected at the thermostat and controls for the AHU is still shorted to the cabinet.

airheatman :

can you tape the wire so it is not shorted ?

Customer:

No. I can't find any place where the insulation is broken on it. I will continue to look and follow along it to see if I can find where the shroud is breeched.

Customer:

Am I correct that this is the entire problem. Somewhere a short occurred on the white conductor and until I either find the short and tape over it or I replace the entire wire, we don't have heat?

airheatman :

Not entirely

airheatman :

You can heat, just not backup heat elements, UNtil you find the short, just leave the white wire disconnected at the thermosat,tape off so it doesnt touch anything.The white is just for the elements.The heat pump still will produce heat in heat mode

Customer:

Makes sense. So we can have heat on the house without the electric resistance elements. Thus, I bought myself a month or two to either find the short and fix it or replace the entire wire.

airheatman :

Lets do this. Power off, reconnect wires at thermostat9all but white) and connect that yellow to Y1 instead of W2 lets see if heat pimp works in heat and cool modes

Customer:

Will do. Give me a few minutes and I will get right back to you.

airheatman :

ok

Customer:

I left the white wire disconnected at both ends. Unit just woke up and the AUX HEAT is flashing on thermostat panel. Compressor is running. AHU just came ON. Will check to see if heat is coming out of AHU.

Customer:

Just felt low pressure pipe and it is getting hot. I will shut it off and switch over to cooling.

airheatman :

wait a second

airheatman :

before you do that

airheatman :

Tell me what the oom temp is and what the call for setting is (example room 70 asking for 80)

Customer:

Yes, we had the room temp at 70 and asked for heat of 72. It was definitely cranking out heat (including aux heat). I already switched it over to cooling. Room temp is 70 and we set it at 66. OK?

airheatman :

ok

Customer:

Still waiting for cooling to come ON. Should be another minute or two.

airheatman :

let me know if air gets cool, will take afew minutes sincecoil is hot,Suction linw should ow get cold,Tstat probably has 5 minute delay betwen\en heat and cool

Customer:

The high pressure line is cold and the AHU just cycled on. It looks like everything is fine with cooling. Can I switch back to heating and see if that AUX HEAT label returns?

airheatman :

Sure, it probably is letting you know your aux needs attention, as ire is dscconnectd

airheatman :

The white wire is second stage or auxillary heat.The reason it sometimes would go for awhile without blowing fuse could be beacuse it didnt get call for aux all the time

Customer:

OK. I look over the thermostat installation manual. It says that the W1 terminal where the yellow wire was previously connected controls Heat Relay #1. The Y1 terminal that I switched over to is supposed to be connected to the Compressor Contactor. Should I switch the yellow wire from Y1 back to where it was originally at W1?

airheatman :

Yeloow should go to Y1

Customer:

Fine. But is a jumper needed to W1 from Y1?

airheatman :

no

Customer:

OK. I will leave the yellow over to Y1 and nothing connected to W1. Also, the thermostat face has an AUX HEAT label illuminated. However, my wife tells me that this does not mean that AUX HEAT is ON. She says that when AUX HEAT is ON, you can smell the dust in the air and there is an AUX HEAT label illuminated on teh right side of the display over by HEATING.

airheatman :

She is correct

Customer:

I will continue to work to find the short on the white wire or replace it. This has been a pile of help. Thanks very much for your very professional analysis in troubleshooting the system instead of these kids coming out (called contractors) just replacing parts until the system "magically" starts to work. I will ask for you alone in the future if I have any further problems and I will pass your name along to everyone at my consulting engineering firm (Datanet Engineering, Inc. of Owings Mills, MD) to help them out when things go bad at home. Thanks Again

airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8,516
Experience: Furnace, A/C and heat pump specialist.
Verified
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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8,516
8,516 Satisfied Customers
Experience: Furnace, A/C and heat pump specialist.

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