Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 09-17-2011, 09:17 PM   #1
Newbie
 
Join Date: Sep 2011
Posts: 3
Share |
Default

VisionPro Outdoor Sensor Reading inaccurate


Hi. I have a VisionPro TH8320 thermostat with an outdoor temperature sensor installed. For about 1 1/2 years the outdoor sensor reading was fairly accurate. I noticed over the summer, it was reading high (I have another thermometer close to the sensor). Figuring the sensor went bad, I replaced it. The temperature reading is still 20 degrees too high. The temperature reading moves up and down, but reads consistently 20 degrees above the actual temperature. Unfortunately, I use this sensor to change from the heat pump to my back up heat source. Any idea what could be causing this error?

bstone17901 is offline   Reply With Quote
Old 09-18-2011, 04:56 AM   #2
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,728
Default

VisionPro Outdoor Sensor Reading inaccurate


Was any new electrical wiring done, that may run near the sensors wires oming back to the thermostat.

beenthere is offline   Reply With Quote
Old 09-18-2011, 09:10 AM   #3
Member
 
Join Date: Aug 2008
Posts: 128
Default

VisionPro Outdoor Sensor Reading inaccurate


If you know how to use a multimeter you can ohm out the sensor to see if it's accurate. You should be able to find the resistance tables on the Honeywell website. It's possible that you got a bad second sensor but not likely. You can ohm it to see. If the sensor is ok then I would be looking at an internal circuitry problem with the thermostat assuming there have been no other electrical changes that could influence the wiring.
kb3ca is offline   Reply With Quote
Old 09-18-2011, 09:13 AM   #4
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,728
Default

VisionPro Outdoor Sensor Reading inaccurate


The resistance chart is in the install manual of the thermostat.
beenthere is offline   Reply With Quote
Old 09-18-2011, 09:20 AM   #5
Member
 
Join Date: Aug 2008
Posts: 128
Default

VisionPro Outdoor Sensor Reading inaccurate


One more thing: Make sure all the wiring connections for the outdoor sensor are tightly connected and not corroded. A bad connection can increase the resistance of the circuit and cause the reading to be inaccurate.
kb3ca is offline   Reply With Quote
Old 09-18-2011, 11:33 AM   #6
Member
 
Join Date: Aug 2011
Posts: 729
Default

VisionPro Outdoor Sensor Reading inaccurate


A higher temp reading indicates that the circuit is shorted somewhere. If you were to take the sensor leads and touch them together, you would read max temperature. Take your sensor off and connect it directly to the thermostat inside. See if it reads the same as the indoor temp after a few minutes. If it does you will need to replace the sensor wire. I would recommend shielded cable.
If the sensor reading is still high take your resistance reading. You should be around 10k ohms at 77 degrees F. If that's ok then its time for a new stat.

Last edited by Master of Cold; 09-18-2011 at 11:42 AM.
Master of Cold is offline   Reply With Quote
Old 09-18-2011, 11:43 AM   #7
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,728
Default

VisionPro Outdoor Sensor Reading inaccurate


[QUOTEA higher temp reading indicates that the circuit is shorted somewhere. If you were to take the sensor leads and touch them together, you would read max temperature.][/QUOTE]

They are negative coefficient. So shorting them together reads the lowest temp.
beenthere is offline   Reply With Quote
Old 09-18-2011, 02:27 PM   #8
Member
 
Join Date: Aug 2011
Posts: 729
Default

VisionPro Outdoor Sensor Reading inaccurate


A thermistor loses resistance the higher the temperature goes. Not the other way around..
Master of Cold is offline   Reply With Quote
Old 09-18-2011, 04:11 PM   #9
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,728
Default

VisionPro Outdoor Sensor Reading inaccurate


Quote:
Originally Posted by Master of Cold View Post
A thermistor loses resistance the higher the temperature goes. Not the other way around..
There are positive and negative coefficient thermistors. But your right, HW does use the negative ones. The controls I'm working on at a place currently, is using positive coefficient. Getting which ones I'm talking about confused.
beenthere is offline   Reply With Quote
Old 09-18-2011, 04:31 PM   #10
Member
 
JJboy's Avatar
 
Join Date: Oct 2010
Location: Austin - Texas
Posts: 1,402
Default

VisionPro Outdoor Sensor Reading inaccurate


Quote:
Originally Posted by beenthere View Post
There are positive and negative coefficient thermistors. But your right, HW does use the negative ones. The controls I'm working on at a place currently, is using positive coefficient. Getting which ones I'm talking about confused.

PTC - Thermistor, Positive - the resistance increases with increasing temperature.

NTC - Thermistor, Negative - the resistance decreases with increasing temperature.
__________________

**Always kill the power ** Hot air rises, but heat will always move from higher to lower temperatures. ** Real man shoot in manual. ** If it ain't grounded, it ain't dead.
JJboy is offline   Reply With Quote
Old 09-18-2011, 04:35 PM   #11
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,728
Default

VisionPro Outdoor Sensor Reading inaccurate


Quote:
Originally Posted by JJboy View Post
PTC - Thermistor, Positive - the resistance increases with increasing temperature.

NTC - Thermistor, Negative - the resistance decreases with increasing temperature.
Thank you.
beenthere is offline   Reply With Quote
Old 09-18-2011, 05:41 PM   #12
Member
 
Join Date: Aug 2011
Posts: 729
Default

VisionPro Outdoor Sensor Reading inaccurate


Quote:
Originally Posted by beenthere

There are positive and negative coefficient thermistors. But your right, HW does use the negative ones. The controls I'm working on at a place currently, is using positive coefficient. Getting which ones I'm talking about confused.
Yes I found this out after I made the heat come on in july..no one in the building thought it was funny...
Master of Cold is offline   Reply With Quote
Old 09-18-2011, 05:52 PM   #13
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,728
Default

VisionPro Outdoor Sensor Reading inaccurate


Quote:
Originally Posted by Master of Cold View Post
Yes I found this out after I made the heat come on in july..no one in the building thought it was funny...

LOL... Brought the heat on in a place where i was using 20,000 and 10,000 ohm sensors on the same stats. I wired them up wrong the first time. Ooops.
beenthere is offline   Reply With Quote
Old 09-20-2011, 06:45 PM   #14
Newbie
 
Join Date: Sep 2011
Posts: 3
Default

VisionPro Outdoor Sensor Reading inaccurate


Hey guys, thanks for the information. Originally, I thought it might have had something to do with the way the builder wired it. On the sensor instructions it tells you to run dedicated wire directly to the tstat and not through the tstat wires. It also says to keep it away from any electrical lines and electric motors. Upon tracing the sensor wires, I realized that they ran the wires into the furnace (near the blower motor) and joined them up with the tstat wires and ran them back to the tstat. But, alas, I multimetered the tstat and the OHM readings were accurate for the outside temp. It appears the issue is with the tstat. Unfortunately, this is the second time I had this problem. The first time, I was still under the builders warranty, so it got fixed on their dime. This time it is all me. Not sure why I keep having this issue, but am thinking about upgrading to a tstat with a wireless sensor. Any thoughts?
bstone17901 is offline   Reply With Quote
Old 09-20-2011, 06:47 PM   #15
Member
 
Join Date: Aug 2011
Posts: 729
Default

VisionPro Outdoor Sensor Reading inaccurate


Shielded wire

Master of Cold is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
VisionPRO Setup Functions & Heat Pump infoskr HVAC 34 11-20-2013 04:24 PM
Honeywell VisionPro IAQ YTH9421C1002 Wiring Help jond777 HVAC 0 11-22-2010 09:22 PM
Heat does not turn off with new VisionPro HoneyPro HVAC 25 10-21-2010 12:40 AM
Honeywell VisionPro Thermostat infoskr HVAC 32 12-17-2008 03:44 AM
VisionPro Thermostat? kcrossley2 HVAC 3 01-27-2007 07:39 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.