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Elk M1G Cannot Read Omnistat2

mstarks01

Member
I have had this problem for quite some time and am finally deciding to do something about it.
 
My Elk M1 Gold cannot read the temperature from the Omnistat 2 RC-1000, connected to an M1XSP . It can send temperature changes, but on the stat it does this weird thing were the new temp flashes five or six times before finally settling down.
 
I have tripled checked all of the jumpers and connections on the M1XSP. I've tried setting the baud rate to 300. All to no avail.
 
The only possibility I can think of is that it has something to do with the wiring. I used 1 pair per terminal of CAT 5 (i.e. orange/striped orange, etc) and I'm wondering if the gauge of the wire just isn't sufficient for the run, which from the M1XSP to the panel is maybe 50 feet. But before I go pulling new wires, I'd really like to confirm this.
 
Any ideas?
 

RAL

Senior Member
Did you remove the COM jumper (J8) on the RC1000?
 
The wire gauge shouldn't be a problem.  A single wire is more than enough for an RS-232 connection.
 
I would not have used both wires of a pair as a single conductor.  Rather, use one wire of the pair as GND and the other as the signal.  That will give you better noise immunity due to the twisted pair.  Not sure if that is what is giving you trouble, but using twisted pairs can't hurt and may help.
 

mstarks01

Member
RAL said:
Did you remove the COM jumper (J8) on the RC1000?
 
The wire gauge shouldn't be a problem.  A single wire is more than enough for an RS-232 connection.
 
I would not have used both wires of a pair as a single conductor.  Rather, use one wire of the pair as GND and the other as the signal.  That will give you better noise immunity due to the twisted pair.  Not sure if that is what is giving you trouble, but using twisted pairs can't hurt and may help.
 
Thanks for your response. Yes, I did remove J8. Interesting thought to ground each pair.
 
What's most curious to me is that I can program the thermostat but not read it, and that the thermostat flashes multiple times each time I send a command. It's almost as if the signal is so marginal that it's right on the edge, but that's just a guess.
 

MarkH056

Member
How new is the Omnistat2? Is it the HAI or Leviton?  I had an HAI installed since 2009, which failed after about 8 years when I had the furnace replaced.  The furnace installer swears the issue is with the T-stat, not the furnace.  But I've sent the T-stat to Leviton for repair, and I can't get it to work.  Was working just fine, but I can't seem to get the Leviton version to work.
 

mstarks01

Member
Thanks for the suggestions guys. I ran new cable in the attic this weekend but have yet to hook it back up. I'll let you know how it turns out.
 

pete_c

Guru
I do not see anything in the pictures except maybe in the first picture a bulging capacitor.  It could be the angle of the picture though.
 
Here also utilize an HAI RC-1000 thermostat with my HAI OmniPro 2 panel.  (over 10 years now).
 
One of the issues I had many many years ago was that the furnace motherboard did not provide enough voltage for the thermostat.
 
That said it would reset when switching it on.
 
Initially purchased an HAI power module which did not work for me.  Then purchased an HAI thermostat relay with an ELK 24VAC power supply.
 
I have not had any issues since the installation of this module.
 
==> HAI 29A00-1 Thermostat Isolation Module.
 

mstarks01

Member
pete_c said:
I do not see anything in the pictures except maybe in the first picture a bulging capacitor.  It could be the angle of the picture though.
 
Here also utilize an HAI RC-1000 thermostat with my HAI OmniPro 2 panel.  (over 10 years now).
 
One of the issues I had many many years ago was that the furnace motherboard did not provide enough voltage for the thermostat.
 
That said it would reset when switching it on.
 
Initially purchased an HAI power module which did not work for me.  Then purchased an HAI thermostat relay with an ELK 24VAC power supply.
 
I have not had any issues since the installation of this module.
 
==> HAI 29A00-1 Thermostat Isolation Module.
 
Thanks for replying. Considering I can control it remotely, I wonder what the difference is between sending commands and being able to read something from the stat.
 

pete_c

Guru
My Elk M1 Gold cannot read the temperature from the Omnistat 2 RC-1000, connected to an M1XSP . It can send temperature changes, but on the stat it does this weird thing were the new temp flashes five or six times before finally settling down.
 
As mentioned above sounds like a serial comm issue and you have replaced the wires.
 
Here when the thermostat was power stealing it would affect the display by constantly resetting the thermostat.
 
Maybe your issue is marginal relating to the power stealing where only the display itself is affected or drawing too much power?
 
You can test this by just connecting a 24VAC power supply directly to the thermostat.  Leave the serial cables and all of the furnace cables off.
 
IE: connect a 24VAC transformer to pins 1 and 3 shorting pins 1 and 2 as in the installation manual for the thermostat.  Make sure the furnace wires are not shorted at the thermostat.  Easier just to pull the thermostat plate off of the wall while doing this.  I have done this on a workbench to test the thermostat and remote programming features via software.
 
Next disconnect the serial cables.
 
The thermostat display should work fine even though it is not controlling anything.  
 
If it doesn't blink when changing stuff on the thermostat then it is the power supply on the furnace motherboard.  If it continues to blink then it is a defective thermostat.
 
It will not function as it is not connected to your furnace but it will just check the PS to the thermostat.  If it works then the thermostat might still be drawing too much power from the furnace motherboard.
 
Have a look inside of your furnace.  Typically the AC transformer is mounted right above the furnace motherboard and is only suited for powering up the motherboard.
 
Most of the ones I have seen are tiny and suitable only for the furnace motherboard.  
 

mstarks01

Member
Thanks, Pete. You may be on to something with the PS. I also recently realized that I can only get it to change temps at 300 baud. Anything higher and it doesn't communicate at all.
 
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