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I’m working on possible the most complicated unique HVAC setup possible. My father’s house has central AC and Oil Heat, in addition to an integrated “whole-house” woodburning stove. There are several relays, transformers, and thermostats involved. I have everything working except for the AC. I can easily solve this nightmare with the addition of one more relay that would kick on the fan whenever the AC compressor comes on.
On the cooling circuit, I have one transformer which is a 220V primary/25V secondary that produces 60 VA. I’m not sure of the specs of the relay that’s inside the compressor itself. I need to add one more relay for the fan on the same circuit. Currently the transformer supplies enough current to operate the relay for EITHER the fan or the compressor, but not both. I’m assuming that I need either a larger transformer, or a smaller fan relay – or both.
Can anyone guide me to the right size transformer and the right size relay to put on this circuit to operate both relays (fan and AC) without frying the electronic thermostat (one of the digital “smart” thermostats from Home Depot)? Can anyone enlighten me on some sort of formula to make the thing work? Is it as simple as adding up the minimum VA for each relay, and making sure that it is lower than the maximum rated VA for the thermostat? Any help is greatly appreciated! Thanks!
-Keith
Replies
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I'm working on possible the most complicated unique HVAC setup possible. My father's house has central AC and Oil Heat, in addition to an integrated "whole-house" woodburning stove. There are several relays, transformers, and thermostats involved. I have everything working except for the AC. I can easily solve this nightmare with the addition of one more relay that would kick on the fan whenever the AC compressor comes on.
On the cooling circuit, I have one transformer which is a 220V primary/25V secondary that produces 60 VA. I'm not sure of the specs of the relay that's inside the compressor itself. I need to add one more relay for the fan on the same circuit. Currently the transformer supplies enough current to operate the relay for EITHER the fan or the compressor, but not both. I'm assuming that I need either a larger transformer, or a smaller fan relay - or both.
Can anyone guide me to the right size transformer and the right size relay to put on this circuit to operate both relays (fan and AC) without frying the electronic thermostat (one of the digital "smart" thermostats from Home Depot)? Can anyone enlighten me on some sort of formula to make the thing work? Is it as simple as adding up the minimum VA for each relay, and making sure that it is lower than the maximum rated VA for the thermostat? Any help is greatly appreciated! Thanks!
-Keith