Maxitrol T115 Override Stat??

[mbreen23]

Quick question. Is the T115 a modulating or a standard thermostat. I'm wondering this because we burned up a A1011A amplifier, and the diagram from our rep has terminal 14 getting straight power from #3 through normally open contacts. Thanks for the help!

[Moose]

http://www.maxitrol.com

[mbreen23]

I've gotten a little frustrated with Maxitrol on this question, I talked to two different tech support guys and got two different answers. None of my suppliers around here have any in stock to ohm out. And the website doesn't have any more information than I already have here at the office. I was hoping someone out there had experienced this.

[Moose]

What is the application? How old is the system -- I can't find that number on the website or in my books/downloads.
Is it possible the numbers are't right? What equipment is it on?

[mtnwrench]

The T115 is pretty much a Johnson controls T26 thermostat. Plain jane no/nc contacts just like a regular thermostat. Crack open a Johnson T26 and compare it to your T115.

[mbreen23]

Thanks mtnwrench, that's the info I was looking for!

[mtnwrench]

Let me add, the t26 is a line voltage stat. Any stat you use should not have an anticipator in it. Just use a normal line voltage stat and you should not have any problems.

[pmerritt]

The t-115 override stat is merely a snap acting t'stat.
It has a rated temp range (dial) and must be mounted inside the space you want to sense. (no remote bulb)
What it actually does when wired into the ts-114 sensor (for instance) is make its set of contacts when the temp reaches its setpoint. When the contacts make, it enables an "over ride" to take place, the over ride setpoint is adjusted on the small potentiometer located on the back of the td-114 selector you are using. It has marked degrees up to 40 degree override I think.
Hope this helps!

[RkyMtnRon]

To pmerritt:

I have a new customer who has three Modine QDA 110A makeup air heaters in a parking garage.

These use the Maxitrol Selectra, Series 14, discharge air temperature control (A1014), with the TD114 remote temperature selector (directly mounted on the units).

The inital call was that all three units were not working. Discovered dirty flame sensor rods and cleaned them. Reset the flame sensor circuit breakers and all three units fired normally and the discharge air temperture control worked.

Problem: Some idiot had disconnected the remote thermostats and just left the wires hanging on all three units. Also noted a different remote t-stat used on each unit, but all were standard residential t-stats (with anticipator wires). One anticipator was fried!

As it is now, when the units are powered up, they run constantly. After reading your very helpful post, I suspect that there may be a jumper from terminal 1 to 2 on the T114 selector or possibly the wire from terminal 2 of the A1014 may be connected to terminal 2 rather than 3 on the T114, but have not verified this.

I can change the three remote t-stats to snap-action types, but need to be sure that I connect them properly, per the Series 14 installation instructions.

I won't be able to get back to work on the units for a few days, but just wanted to ask if you agree with my logic or have another suggetion.

[pmerritt]

Hi Ron, Most of the MAU's I am familiar with will run constantly until shut down, i.e. maintain a constant discharge air temperature (per TS114)
until they are shut down.
Depending on how one wants to control the unit, you might use a line voltage stat, manual toggle switch on a panel (summer winter sw.), or a low voltage stat that fires a relay.
Are you wanting to run the blower continuously and use a thermostat to turn the burner on/off, or do you wish to run the MAU only until the room temp is satisfied and shut the unit down?
Most of what I see is a toggle switch turns the blower on, a damper opens allowing the blower to start, the airflow interlock makes, the flame protector circuit runs through its sequence, and the burner fires. At this point, the Maxitrol circuit maintains a desired discharge air temperature, according to the temp selector dial. (You likely already know this)
If you want to shut down the unit when the room temp satisfies, simply break the line voltage between the control (toggle)switch and the unit control transformer.

The T115 over-ride stat is simply a snap acting stat which is wired to the A1014 so a higher temp can be achived during the time the T115 is in the circuit. On the back of the temp selector there is a little arm (looks like a heat anticipater adjustment) there are numbers there from 10-40 degrees. You can select what you want, and when the T115 closes, the unit discharge temp will rise to reflect that setpoint.
Hope this helps....Paul

[RkyMtnRon]

To Pmerrit:

Hi Paul:

Thanks for your prompt reply.

In this installation (in an underground parking garage, below a 3-story apartment building), there are a series of CO sensors that control exhaust fans (2 intake and one exhaust, plus one exhaust that runs 24-7).

There are exposed drain pipes in the parking garage. The purpose of the MAU's is to prevent the temperature from dropping to low, in the winter, to avoid frozen pipes.

The three remote thermostats (all located about 30' away from each MAU) are to turn on the units if the temperature falls below the t-stat set points (about 40°F).

I don't want to override the discharge air temperature control, I just want the remote t-stats to control the MAU's as originally intended (Turns them ON when below 40°, OFF when above 40°F).

Should not take any extra relays, because at one time these units were working (according to the building owner).

My problem is that I have not been able to figure out where these remote t-stats were originally connected and the available documentation and wiring diagram has not been any help (shows no connections for a remote t-stat)!

I have contacted Modine's customer support department, they refered me to their local sales rep company. So far these guys seem clueless to provide any real help.

I've been tearing my hair out over this one (and there is not much left!).

Any further suggestions?

[pmerritt]

Ron, it looks like you will have to do a bit of detective work to determine whether to utilize low voltage or line voltage t'stats.
If the wiring diagrams are illedgable, start clipping cable ties!
You need to put the t'stats in the circuit BERFORE it gets to the maxitrol portion of the system.
Is there a damper on the inlet or on the outlet of the heater?
If there is, find the power source for the damper motor, and cut the t'stat into that. Then, when the t'stat makes it will allow the damper to open, thus starting the sequence of operation.
If there isn't dampers, then I would find the control power for the blower motor starter (contactor coil) and put the t'stat in series with that.
Make sure to determine what coil voltage is used, and use the applicable type of stat.
Hope this helps.....Paul

[RkyMtnRon]

To Pmerritt:

Hi Paul:

Thanks for your continued interest and support.

Think I finally figured out what has been going on and have a solution. This has been one of the oddest problems that I have ever encountered.

Looks like there was a misscommunication of some type when these units were originally specified, ordered and installed.

I found a copy of the original unit order. No relay was specified for an external remote area thermostat! So one was never installed!

The unit schematic shows an "optional" door interlock switch, on the 24 volt side of the control wiring. This was not ordered or installed. It is bypassed by a short 22 ga. jumper wire on the auxiliary terminal strip. If I remove the jumper, the unit shuts down (as expected).

Checked the main fuse for the 24 volt control circuit. It is rated for 32 volts @ 10 amps (Buss MDL-10).

Looks like someone tried to use these jumper terminals for the remote thermostats, but of course the current was too much for the t-stats to handle without a small relay, so they fried the t-stat's anticipator wires! (DOH!). Eventually, they just gave up and left the t-stat wires hanging in the MAU's!

I have no idea what the original t-stats were (no records), but trying residential t-stats was the wrong move.

Since the only purpose of the MAU's is to prevent pipes from freezing, they should have used non-adjustable "construction" t-stats, preset at 41°F. If used with a small 24 volt relay, they will work fine, even if they have anticipators, as long as the anticipators are set above the relay coil current.

So, it now appears as though these MAU's have never worked properly, from day one! I am checking with the building owner to try to confirm this. Seems that the property management company's maintentence techs were totaly over their heads on trying to resolve this issue. They also failed to do any annual maintenance on the flame sensor rods.

I plan to install a DPST, 24 volt relay, rated for 10 Amps, tie the two poles togeather for redundancy and use the relay to replace the optional door interlock switch jumper. I will select a relay with a coil current of .2 amps or less.

I am also going to eliminate the existing t-stat wiring that tied them to the CO sensor control system to shorten the total loop length. That will cut my longest t-stat wire run to about 100', so will reduce potential voltage drop. This will also allow the MAU's to run, based on garage temperature only, not just when the CO sensors activate the fans (another apparent system design error).

Thanks to you, I have managed to come up with a workable solution to a very long term problem for this building owner.

I greatly appreciate you insites and advice.

[pmerritt]

You are welcome Ron, although I am sure you would have come to the desired solution once you had time to think it over.
Paul