Question about Honeywell YTH9421C1002 VisionPRO IAQ Thermostat and Equipment

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Honeywell VisionPRO IAQ thermostat. No back light. Screen shows characters, but dim. When touched, back light fails to work. All other systems function okay.

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  • 26 Answers

This control has an option for back light display in the set up menu. if it has never worked this may be the problem. if it did work then quit you should replace the t-stat. there are many different models as they have advanced over the years. this is a great control. see if you can find the set up manual

Posted on Oct 15, 2013

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Posted on Jan 02, 2017

AcJim
  • 107 Answers

SOURCE: The touch screen on my

Unfortunately it sounds like it is time for a new thermostat. I deal with these alot and sometimes they quit responding and have to be replaced.

Posted on Dec 23, 2010

mercadoarvin
  • 384 Answers

SOURCE: honeywell thermostat VisionPro IAQ flashing

Welcome to Fixya.

This error code implies "heating or cooling equipment missing"- on easier terms, something might be disconnected or incomplete as you may not have everything hooked up. If so, you need to go to the installer menu to make sure you have the correct settings.

Here's a user's manual just in case :

VisionPro User's manual

Thanks for using Fixya.

Posted on Jun 04, 2011

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1 Answer

Why is it showing error code 90?


Sounds like a all the bells and whistles thermostat, why did you chose that one?
090 Data interface is continuously busy.
A log of error codes can be viewed at the end of the installer setup after the system tests. Active errors will be shown first. The Error Log will log the last ten errors (active and inactive).
Pressing the reset button will clear all inactive errors from the
error log; active errors can not be cleared until the condition has been remedially busy

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1 Answer

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Remove your thermostat from the wall and you probably will find a battery compartment in the rear.

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Honeywell TH9421C1004 blank screen after power outage


We'd love to help resolve this. Please give us a call at 1.855.733.5465 and our customer support team will be happy to troubleshoot with you.

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1 Answer

Auto does not show in system


On Honeywell thermostats you have to program the thermostat on the setup mode to have the auto to be on the display. The setup instructions will walk up through it. If you do not have them, you can down load them to you computer.

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Make sure there is 24 Volts between the R & Common wires connected to the thermostat subbase.

Dec 13, 2013 | Honeywell TH9421C1004 VisionPRO IAQ Total...

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Pull the thermostat face off the wall. Wait a few minutes, & gently line up the pins and place back on. Let display pull up. If that doesn't work, your thermostat is probably under warranty...Replace.

Dec 13, 2013 | Honeywell TH9421C1004 VisionPRO IAQ Total...

1 Answer

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check your float switch. On your air hander you have 3/4 white pvc coming out of bottom of unit, where the water drains out. If you have a float and your drain line is plugged it will make your tstat go blank. vacuum the drain line where it comes out of the ground outside.

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Honeywell 8000 Thermostat relay switch clicking noise.


It's an expensive solution but doable. Look for Honeywell's VisionPro IAQ thermostat. It works much differently than a conventional thermostat and shouldn't click at all make sure it's the 3-wire version.

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