Furnace time delay relay for AC staging

[Wildblue19]

Anyone here know how furnaces are wired? It is truck related I promise.

Long story short, I am running 2 AC compressors in my truck and I'd like a delay between the two compressors turning on. I don't want to load down the engine with two compressors switching at once.

There's also a requirement that the systems cycle independently. Both compressors have a low pressure cutoff switch. I don't want one switch tripping to cut power to both clutches.

I found this furnace relay which has a 4 second start delay and 2 minute shut off delay. I don't know if it will work and the manufacturer website obviously isn't helpful toward my situation.

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I imagine the controller senses when the t stat is engaged, and then waits 4 seconds to send 12v to the motor. When the t Stat shuts off, the motor runs for 2 minutes.

In my case, 12V will be IGN 12V. T Stat will be the #1 compressor with the low pressure switch in series. Motor will be compressor 2 with its own low pressure switch.

If system 1 triggers the low pressure switch, I get 2 minutes of the second system before the relay cuts power, which should be plenty. If compressor 2 triggers it's low pressure switch, system 1 is unaffected.

Any furnace guys think this is reasonable? Issues I can forsee are the relay seeing 14v and not a pure 12v signal, as well as the inrush current through the controller if system 2 triggers and connects the "motor" pin to ground when it's not expecting it to.

 

[1998_K1500_Sub]

Anyone here know how furnaces are wired? It is truck related I promise.

Long story short, I am running 2 AC compressors in my truck and I'd like a delay between the two compressors turning on. I don't want to load down the engine with two compressors switching at once.

There's also a requirement that the systems cycle independently. Both compressors have a low pressure cutoff switch. I don't want one switch tripping to cut power to both clutches.

I found this furnace relay which has a 4 second start delay and 2 minute shut off delay. I don't know if it will work and the manufacturer website obviously isn't helpful toward my situation.

You must be registered for see images attach

I imagine the controller senses when the t stat is engaged, and then waits 4 seconds to send 12v to the motor. When the t Stat shuts off, the motor runs for 2 minutes.

In my case, 12V will be IGN 12V. T Stat will be the #1 compressor with the low pressure switch in series. Motor will be compressor 2 with its own low pressure switch.

If system 1 triggers the low pressure switch, I get 2 minutes of the second system before the relay cuts power, which should be plenty. If compressor 2 triggers it's low pressure switch, system 1 is unaffected.

Any furnace guys think this is reasonable? Issues I can forsee are the relay seeing 14v and not a pure 12v signal, as well as the inrush current through the controller if system 2 triggers and connects the "motor" pin to ground when it's not expecting it to.

This really isn't a furnace question, it's a component question.

The component in this case is delay relay that has applications in furnace control and possibly other areas. It may be one of a family of similar components that have different delay characteristics, i.e., other than 4s/2min.

I would try to find a spec sheet for this device to see what else could be learned. However, it's pretty simple and seems likely to work as you intend.

Provided it's used within its intended parameters (voltage, current) you should be fine.

Nexem makes the relay that's a part of that device, and the relay's p/n is readily visible. You can at least determine the current allowance (and possible need for a flyback diode) by studying the relay's specs (see link).

It seems pricey IMHO from the vendor you cited. You might try to find it from another vender (DigiKey, Mouser, etc.) for less.

Neat device! Nice find

https://www.onlinecomponents.com/en/nec-relays/ep1fb3g1s-45586028.html

 

[Wildblue19]

@1998_K1500_Sub Agreed - the furnace line was a bit of a joke. I will email the company and see if they are able to talk about my use case. I already have a ton of arduinos, logic level MOSFETs, etc to make it myself...but if theirs works, I'd prefer it!

 

[1998_K1500_Sub]

@1998_K1500_Sub Agreed - the furnace line was a bit of a joke. I will email the company and see if they are able to talk about my use case. I already have a ton of arduinos, logic level MOSFETs, etc to make it myself...but if theirs works, I'd prefer it!

Considering it’s for an RV application, where “12V” likely means the same as it does in other vehicular applications, I think you have a winner.

Check the current and other specs on that Nexem relay, that’s where the business happens.

I suspect you already know all this

 

[1998_K1500_Sub]

I will say, this device has a number of things going for it:

- it's potted and weather resistant, so that objective is met

- connections are simple push-on AMP Faston tabs, although you could likely solder to them (with care)

- it's natively 12Vdc

- the delay values are usable


There are others, e.g., there are three different ones at this link, two "delay on release" and one "delay on operate":

Time Delay on Release Relay - 12V DC, 30 Amp

Looking for an adjustable relay that can maintain a power supply for as short as 2 seconds or as long as 3 minutes? Shop Del City's 12 volt time delay relay.

www.delcity.net

 

[Supercharged111]

Couldn't you put a capacitor between the relay coil ground and the ground itself to get a delay on actuation? I seem to recall it delaying of off function when placed in front of the coil. It's been a while since I'd looked into this function but it isn't difficult to DIY. And I'm not sure you want that 2 minute delay to turn off function.