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Old 07-17-2012, 07:26 PM   #1
TWX
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Override for heatpump in workshop


Hey everyone, nice forum you've got here...

I have a workshop with a heatpump. Sometimes while working on a car I need to open one of the doors to avoid asphyxiating myself, and I found some switches that might, with the proper circuit, let me cut off the AC when one of the big doors is open. Unfortunately they're normally closed, momentary open, so I'll probably have to use relays. What I would like to do is to cut off power to the 24VAC circuit telling the compressor to run, while leaving the air handler (split system) running. That would allow airflow to help clear out if needed.

I figure that if I run 24VAC to each switch in parallel, if their portion of the circuit is open then a relay they're controlling would remain closed, letting the system run. If either switch closes, the relay would open its circuit, disconnecting 24VAC from the compressor-activate wire between the thermostat and the compressor.

Does this sound right?

BTW, the switches are GS Edwards #44. I was planning on installing them at the tops of the rolling doors, so that when the doors open they let off pressure as the tops pull away.


Last edited by TWX; 07-17-2012 at 07:28 PM.
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Old 07-17-2012, 09:46 PM   #2
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Override for heatpump in workshop


a standard toggle switch will work... or light switch.... Break one of the 2 wires going to the condenser with the switch. Problem solved.

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Old 07-17-2012, 10:17 PM   #3
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Override for heatpump in workshop


Can't be in parallel, has to be in series.
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Old 07-17-2012, 10:42 PM   #4
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Override for heatpump in workshop


They actually can't be in series either, as they're normally going to be open (pressed), so I guess I'll have to have two separate relays controlling the same thermostat wire...
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Old 07-17-2012, 10:50 PM   #5
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Override for heatpump in workshop


Just use a regular contact switch. keep it simple.
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Old 07-18-2012, 03:39 AM   #6
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Override for heatpump in workshop


I'd aLso suggest that you be sure your condenser has a Delay on Off timer to protect the compressor. When that compressor is turned OFF, it should stay off at least 5 minutes to insure you don't short cycle it.
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Old 07-18-2012, 01:25 PM   #7
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Override for heatpump in workshop


I also re-iterate what scott is saying. Definitely put a time delay in the circuit, otherwise, if someone opens the door and closes it within a minute, the pressure in the lines may not have equalized and the compressor is going to have to work really hard to get going again.
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Old 07-18-2012, 08:06 PM   #8
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Override for heatpump in workshop


good to see you posting in the HAVC forum again AndrewF.
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Old 07-19-2012, 09:03 AM   #9
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Override for heatpump in workshop


Thanks everyone. I'll put my gauges on and see how long it takes. This was prompted in part by my leaving a remote for the garage door in my pocket and inadvertently leaving it open for several hours in the afternoon here in the Phoenix area. Thankfully I did it on a day that had seen significant rain so it wasn't a whole lot warmer outside than the thermostat was set to, but another day and there could have been a 20-30 degree difference and that might have hastened the end of my already fourteen year old unit. We just put a new unit on the house, so I'm painfully aware of how expensive replacing it will be.

I'm also planning a circuit to illuminate some pilot lamps in the house for when any of the three doors are open. I'm kind of thinking that I might be able to use a second 24VAC transformer to power that circuit (which would function best pushed-open, released-closed actually) and then using relays from that circuit to interrupt the air on the other circuit.

With the need to avoid short-cycling, I'm tempted to put a five minute timer on the cutoff too, so that simply opening the door to pull a car in and closing it doesn't cut it off, but if it's open for too long then it would.

I'll have to think on this a bit and draw something up.

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