Variable speed furnace question

Reply

  #1  
Old 02-13-12, 02:28 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
Variable speed furnace question

I recently had a new Tempstar variable speed furnace/ac installed.

Installers did a nice job, however it is not running as it should.

Stat calls for heat, furnace comes on ( at only one speed ), warms house up to desired setting ( new thermostat installed by the same guys ), then shuts off.

Well, I paid for the top of the line unit... being variable speed two stage... but the blower speed does not gear down at any time.

I went to a home show yesterday & talked to 6 or 7 different guys about how a variable speed furnace works and they all said the same thing-- it should operate more often at a lower VARIABLE speed.

I'm thinking that some of the setup (dipswitches ) are not in the proper positions.

Specs... Tempstar # f9mvt0801716a
96% 80,000 btu

White Rodgers/Emerson Thermostat # 1f83-0422

The company that installed this has been in the HVAC business since 1949, so they know their stuff. I'm just afraid that this unit is so new that they may not be completely familiar with how to set this up to operate as it should.

They installed a chimney liner, coil, condensate pump, humidifier, Air Guard air cleaner, the works !

They came back today after talking to somebody at the manufacturer, said they changed some settings. But the unit is still not operating at a lower speed.

Any input would be greatly appreciated...!!
 
Sponsored Links
  #2  
Old 02-13-12, 03:47 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
Received 0 Votes on 0 Posts
are you sure that it is not operating on 1 stage (low) and never needing to go to 2nd stage (high)? This would indicate an oversized furnace, or really low demand due to warmer than normal outdoor temps. Check to see that W2 is wired to the thermostat and furnace.

Here is your install manual. http://www.managemylife.com/mmh/lis_...L/1109764L.pdf
 
  #3  
Old 02-14-12, 02:14 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
I checked W2 & it is connected, blue wire on thermostat and on furnace board. When it runs, it is only at one speed (not sure if it is high or low ).

If I increase thermostat 1 or 2 degrees, it indicates "system on".
If I increase it 4,5,6 degrees it indicates "system on +2".

Both cases, blower is at the same speed.

I just think this is a newer unit that the installers may not be as familiar with.

Did I really throw $1000.00 plus away for a "variable speed ECM circulation blower motor" and "two stage self adjusting operation"?

As I understood during initial sales meeting, It will run at a very low (or variable speed ) most of the time to keep the house consistently warm" and ramp up to higher speeds if the temperature drops.

Anything else I can check before calling my guys back ?
 
  #4  
Old 02-14-12, 05:09 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
Received 0 Votes on 0 Posts
A volt meter would be necessary to check it thoroughly. DO you have one and know how to use it? Or if not then you would need a set of jumpers.
 
  #5  
Old 02-14-12, 06:08 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
Yes, I have both meters and jumpers.
 
  #6  
Old 02-14-12, 06:13 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
Received 0 Votes on 0 Posts
ok. Blower door off and door switch taped. Turn thermostat up to call for heat (only 1 degree above room temp). Measure AC voltage between W1 and C and W2 and C. You are looking for 24VAC nominal. At only 1 degree you should only see voltage on W1. IF you turn the stat up more you should see voltage on both W1 and W2. Post your results.
 
  #7  
Old 02-14-12, 10:08 PM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,988
Received 35 Votes on 30 Posts
The airflow should increase when it upstages.

80k @ 96% afue is a lot of heat - hope your house is large or poorly insulated, otherwise it's oversized.
 
  #8  
Old 02-14-12, 10:11 PM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,988
Received 35 Votes on 30 Posts
A jumper or dip switch setting may need to be changed to allow the t-stat to control staging.
 
  #9  
Old 02-16-12, 02:29 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
25.5v at W1-C
0 at W2-C

Turned thermostat up 4+ deg. & got 26v at W2-C with no change in blower speed.
 
  #10  
Old 02-16-12, 02:45 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
Received 0 Votes on 0 Posts
Did the firing rate and inducer speed change?
 
  #11  
Old 02-16-12, 02:49 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
I'm not sure what that means. I just went upstairs to turn up stat until "system on" turned to "system on +2", then went back down to check voltage at W2-C.
 
  #12  
Old 02-16-12, 03:00 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
Received 0 Votes on 0 Posts
You need a helper to do this properly. Or you need to control at the furnace with jumpers. By being at the furnace you cant tell exactly what is changing it was not changing.
 
Reply

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


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: