Time delay relay in circuit?

[Calgaryhvac]

I was at a job recently for a fan unit not working properly.

This is a unit that utilizes a zone valve and either hydronic heating or cooling.

The condo has both a chiller and a boiler so the building runs either hot or cold water through the system (never both at the same time).

While inspecting the fan I saw what appears to be a time delay relay. (I’m not that familiar with this).

The relay wasn’t included on the wiring diagram.

What do you think the time delay relay is delaying?

fan on?

Thanks, photos attached - PLEASE disregard first photo - that was a mistake.

[Calgaryhvac]

Also - how is it that the time delay relay only has 3 wires? Don’t most relays have 4 wires?

[BBeerme]

Common, 24 vac, load.

Does that unit have electric heat strips? Looks like its more of an off delay for the blower.

[Calgaryhvac]

It does have heat strips. I guess my question is?

Conventional relays have power in/ out for the coil and power in/ out for load.

This relay appears to have power supplying load and relay from a single wire which splits into a parallel circuit:

Is that correct??

[BBeerme]

Essentially, yes.

[Canadian Tron]

I would guess fan on delay to allow the coil to cool down or heat up (season dependant) before fan on.

[Calgaryhvac]

Yeah that’s what I thought too. Surprisingly, my newest complaint at the building is that a person has “only cooling”.

The building has heat/ cool stats but only 1 zone valve with both heating and cooling wired to a single zone valve.

The issue that has come up is in heating - the stat opens the valve when the room is cool.

In cooling mode, the stat closes the valve when the room is cold. (N/C zone valve).

LOL the occupant called and said “my room is freezing - I have it on heating and the room is at 15 Celsius. (Building is running chiller) and chilled water through zone valve.

The more she selected heat, the more the zone valve opened, allowing ice. COld water through the coil.

I instructed her to turn temp down - heat came up. Easy money call for Monday morning.

[Tom27]

Thats for the heater. Keeps the fan on after the t'stat is satisfied.

[ehsx]

Vendor lists it as a duty cycle timer, typically used for defrost or just for air circulation. Not sure how used in you application. Would be based on wiring and settings.

https://www.icmcontrols.com/productdetails/ICM305

[leLemur]

I'm guessing it's for the fans wen it needs to ramp up

[slctech]

I guess I am kind of wondering if they have hot water heating, why the electric heat?

I am envisioning a large condo or apartment complex with a main chiller for the summer and boiler for the winter, essentially just a basic two pipe system running from floor to floor and to unit to unit? Some poor fellow (usually myself) in the fall must make the decision to switch over from the chiller to the boiler and vise versa in late spring, always have mother nature sneak a unseasonal hot or cold day in after the change over and the calls come blaring in from the temperature sensitive tenants/owners. I envision each unit has buried above the ceiling a PIA air-handling unit behind a metal ceiling access that only a contortionist with 6ft long arms and Arsenio Hall fingers can access. A 3-wire temperature change over-switch that is a b!tch to get to and the little metal fastener is missing or broken so five or six zip-ties, electrical tape, and some thermal paste is keeping it hanging to the supply pipe. When that switch takes a grunt or falls off, or whatever, the tenant's thermostat is operating in retard reverse, heating is cooling and cooling is heating....oh I do not miss those buildings.

As for the delay on make/break timer, it is super common in our industry, but without a step back photo of how it has been introduced to this unit, all we can do is speculate. Just a WAG but part of me is wondering if this is to prevent short cycling of the heat strips. Not sure what you have there for a thermostat or if thermostats vary from unit to unit, but wondering if there wasn't the occasion that the a cheap thermostat is just on the RCH (a blonde one) of needing heat and that would chatter the relay and the heat strips, and not seeing a sequencer in the drawing, so I imaging the rapid on and off of them elements could have drove a handy man mad with tripped breaker, so a delay installed for a 1 sec delay to close and then appears to be a 255 second (4.25 minute) delay to open.

[Calgaryhvac]

slc tech - that was it. You described the entire building and situation so well it made me laugh.

Thanks for the reply!

[ehsx]

Just an fyi. When a ss timer or t’stat doesn’t have a dedicated neutral and another ss device is downstream they sometimes don’t work.

I’ve had the problem with t’stats (no common) & solid state furnace controls, time delays ( 2 or 3 wire) & motor protectors.