Thermolec Electric Duct heater

[newgage]

Model: SC-CTPB
S/N: 153400-001
Application: Hallway pressurization, 100% fresh air.
If anyone is familiar with the operation of these units I have some questions.

It has a D35 control module and a DT1040 Duct thermostat.

Thermostat has been changed out. All Three banks of heaters are funtional.
C1 contactor and C2 contactor modulate and maintain temp.

When C3 pulls in the hallway will overheat.

I was told from Thermolec that C3 pulls in at 90% demand and cuts out at 35% demand. That doesn't totally make sense to me. Can anyone help explain c3 operation.

[macgivor]

Are you sure it is 35% before it pulls-out? Mabey it's
75 or 85% and the 3 was misread?
If it is 35% that would help explain why the hall
overheats since the 3rd heater hangs in there too long,
also, is the 3rd heater controlled under the t-stat
or is it just an on/off operation when it is its turn to
be sequenced on, and therefore stays on regardless of t-stat
and stays on until a low of 35% demand is reached?
By the way, what kind of control or sensor (what method)
is used to determine this percentage of demand?

[orion242]

>By the way, what kind of control or sensor (what method)
is used to determine this percentage of demand?

Something with a PID loop or similar control scheme.

Looking at the website the D35 has 4 inputs:

Thermistor thermostat (DT or RT), 0 - 10 VDC, 4 - 20 mA, 0 - 135 Ohms

It has two outputs, one for SSR control and a second aux output.

How are the three contactors terminated to this?
Is this unit equipped with SSRs or true contactors?

There looks to dip switches on the front of the module labeled relay hysteresis, you may want to play with this. Without a manual I’m flying blind, and they don’t have much info online.

[newgage]

Thanks for replies.
I am still waiting for operating manual and sequence of operation from thermolec.

Their tech support recently told me it should have an outdoor air thermostat. I went back to the site. There are two MUAs, one for each wing of the building.
They are slightly different in configuration.

The south side - I see the problem more clearly now. A thermostat is required to pull in C3 contactor (second stage). Original installer did not put one in and the contactor only has hot side of control (24V) hooked up. So needless to say , the second stage is non functional at this point but can be easily remedied with a mercury thermostat to pull it in at 35F when they seem to have cold hallway temps.

The north side however, is slightly different and is the one that overheated hallway temps. Tech support said it should have an outdoor air thermostat. It also does not have one. I find it a little frustrating they have not given me the literature or a good explanation of this 90% / 35% thing.

I think I will wire this one the same as the other side. Bypass the relay for second stage and control it from a mercury stat sensing outside air intake. Close on a fall in temp at say 30 to 35F will pull in the second stage. The DT 1040 controller should modulate C1 and C1 contactors to control supply air temp at my setpoint of 70F.

I did check to see if first stage modulates properly by adjusting temperature and seeing if supply air stablized o different set point. That part seems fine.