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I replaced my thermostat last night without

I replaced my thermostat last night with a Honeywell RTH7500D without turning the power off, and it is no longer working. From what I have read I may have shorted out the transformer, how do I tell if this is the issue?

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  • joshuageforo May 09, 2010

    Can you tell me where this transformer would be located at?

  • joshuageforo May 09, 2010

    Can you tell me where this transformer would be located at?

  • joshuageforo May 10, 2010

    Can you tell me where this transformer would be located at?

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Check for 24 volts ac at R & C terminals at the t-stat. Your transformer will have 4 wires hooked up to it. Two on one side and two on the other. Two of them will read either 120v or 240 v ac depending on whether you have a 120 or 240 v voltage. The other side should read 24 volts. If you are not reading 24 volts, then you have burnt the transformer and will need to replace it. If you are reading 24 volts, check to see if there a low voltage fuse located on the control circuit board or somewhere between the transformer and "R" terminal.
Here's a picture of a typical low voltage transformer found in an A/C system:


If you replace the transformer, add a 5 amp fuse on one of the 24 volt leads......this will save you from having to replace another transformer in the event of future "short" in the low voltage circuit.
Contact me with any questions or concerns.

I hope you find this to be very helpful to you moving forward,

Please leave a rating. :-)I replaced my thermostat last night without - f0b3aee.jpg

Posted on May 09, 2010

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  • laura Newman May 10, 2010

    Hi Josh,

    The transformer is normally located in the indoor unit's control department which is normally located close to the blower section (the blower is the fan that blows the air through your house).

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Honeywell RTH7500D Thermostat


This Honeywell thermostat is a good medium priced thermostat that will give you many bells and whistles at a very good price. The programming is very easy to do and of course the thermostat is very reliable also.

4351a52.jpg

The installation of this thermostat is very easy and if you need help with the installation you can go here to see the complete installation guide.

http://customer.honeywell.com/techlit/pdf/PackedLit/69-2221ES.pdf

If you have lost your owners manual and need a copy of it you can go here

http://customer.honeywell.com/techlit/pdf/PackedLit/69-2222ES.pdf

With the help of these .pdf files you can get all the information that you need to install and troubleshoot your RTH7500D thermostat.
If you are replacing a thermostat make sure that you turn off power to your heating or air conditioning system BEFORE you start removing any wires. Failure to do so could cause you to burn out the 24v transformer of your system. Also make sure to mark all wires well before removal so that you know which wire went where and so that you can reinstall the old thermostat as it was if something goes wrong with the new installation.

For heat pump systems you WILL have to make some programming changes to the thermostat to get it to work with a heat pump system. Most all thermostats come programmed for conventional systems. This reprogramming is not difficult but is required for proper operation.

http://www.fixya.com/support/r3623083-thermostat_wiring_terminal_designations

http://www.fixya.com/support/r3892721-programmable_honeywell

http://www.fixya.com/support/r3894275-manual_honeywell_find_honeywell_manuals

on Jan 16, 2010 | Heating & Cooling

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The Honeywell model RTH7500D is nice, simple programming is why I love it. Home Depot has it for around $50 I think. Good luck!

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probably tripped a limit switch or a low voltage fuse would kill your display on the tstat, you should have battery power on your stat though.unless you have knowlege of electrical you better call a technician

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Letter designations for honeywell tsats R=24 volt power, W=heat, Y=cooling, G=fan, C=common wire for the 24volt power to tstat. Generally R is the red tstat wire and so on. Blue tstat wire can be hooked up to common at the tstat. On the heater the blue tstat wire would be hooked up to the C terminal. But this also depends on the manufacturer of heating unit.

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How do I calibrate the temperature for the RTH7500D thermostat? It is 2 degress warmer than the thermostat reflects. Does this thermostat operate on the battery power alone? There are only two wires going...


There is no feature in this thermostat to adujust sensor. You need to make sure you have picked for hot water systems.

Follow blue link for instruction manual

If you need more information, please post back.
If this answers your question please hit accept

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