Original message
| stevewp
 |  "common wire used for on 7300honeywell?"
, posted Wed 23 Nov 11:31:  
In an attempt to reduce our energy demand, our church is trying to replace our traditional thermostats with programmable thermostats.
The honeywell Series 2000 Commercial thermostats with Q7300A subbases were purchased. The electrician in our group feels we have to have 5 wires between the thermostat and the furnace.
We have several furnace and a/c units in the buildings to heat/cool different zones in the buildings. All are single stage and 1 thermostat controls 1 furnace / air conditioning set.
Here is the way we understood the diagram from Honeywell's "Typical Wiring Hookup"
1. RC is jumpered to RH (per honeywell's comment: JUMPER RC TERMINAL TO RH TERMINAL WHEN INSTALLED ON A SYSTEM WITH ONE TRANSFORMER)
2. Y1 (normal color YELLOW) is connected to the Cooling/Compressor Contactor
3. G (normal color GREEN) is connected to the Fan Relay
4. W1 (normal color WHITE) is connected to the Heat Relay
What the electrician is telling me is that we have to have a 5th wire from the "C" terminal to the "other side of the heating transformer"
We have an older building and we cannot run a new cable if the extra wire is required.
I cannot find a "C" terminal on the honeywell subbase schematic.
In my way of thinking, the RH and RC union are to be connected to the positive side of the DC transformer (all of time time). When the thermostat calls, for instance heat, the W1 terminal is connected to ground (within the thermostat) which connects the negative side of the heating transformer to ground. This completes the circuit and the transformer is engergized.
The fan control and cooling controls behave similarly by switching the negative side of the transformer/relay to ground - completing the circuit.
I am working on the financial side of the problem and need the thermostats installed ASAP to avoid high heating bills.
Can someone explain to me what terminal "C" does (its not on our schematic from honeywell). We do have C1, C2, C3, C4, C5 but these are to be used with a remote comfort adjust module. We are not using this module. The thermostat wiring guidelines from this site explain that C terminal is typically connected to BLACK (24 VAC Common).
Why would a simple replacement of traditional thermostat require a 5th wire?
Is my understanding of how this works wrong?
Does anyone know of a way to contact honeywell to explain our particular problem so we can resolve this issue?
[this message was edited by stevewp on Wed 23 Nov 11:32] |
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| Archangel
| "Re(1):common wire used for on 7300honeywell?" , posted Fri 23 Dec 01:40
That's a lot of stat, very expensive $$$$.
I know it's prolly too late, but there are plenty of other choices for programable stats that use what we call "Power stealing". these stats can operate fine on 4 wires.
Assistant Trades Supervisor HVAC
17 years exp.
Licensed
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| harpo
| "Re(1):common wire used for on 7300honeywell?" , posted Tue 29 Nov 19:41
that "C" they want is the other side of the transformer.with digital stats it takes a TRUE 24V to run it...R and C.the X is the COMMON there and if you can't pull a 5TH wire use the Y1 for now in the heating season.remove it and flip it to the X at the subbase and C down on the furnace.have the electrician read that at the subbase also to verify that 24V sooner or later you will have to pull new wire.
It ain't going to get any lighter looking at it!
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| TechMaster
| "Re(1):common wire used for on 7300honeywell?" , posted Thu 24 Nov 11:39
You do need the 5th common wire to power up that thermostat. It is probably the X terminal on the subbase. If you can't run the common wire, then you could get a thermostat that runs off batteries.
Keep Cool!
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