Mod: Fixed fan AC to thermostatic fan AC
When I got my Carrier Air V Secondary AC unit, I obtained the basic distribution head to attach to it. This has a simple panel switch that has five positions - fan low, fan high, off, AC low, and AC high.
However, when the AC Low and AC High selections are chosen, the fan blows continually, and the compressor cycles on and off. That is adequate to the task of cooling the RV - but its noisy. I hate the noise enough when its cooling. But to hear it when its not? Unacceptable. So, I decided to mod it so that the thermostatic control also controls the blower motor.
Mission: Make the blower motor thermostatic.
Tools: My favorite power driver by Makita, an extension, and a #2 phillips bit
Step 1: Disconnect the power.
Step 2: Remove the bezel to get at the wiring.
Step 3: open the wiring boxes. Mine has two - the smaller is the 'Do Yourself' power connection box, and the larger is the wiring box that contains the actual guts.
I removed most of the screws, then found there was one sneakily concealed kind of behind the connection box. Here's my driver getting at it with an extension.
Step 4: Inspect your wiring.
So what have we here? Contact 1 is obviously the power, the black wire that comes from the connection box.
Referring between this photo and the chart printed on the box.
contact 1 is obviously the power.
whenever the low fan is on, contact 2 is made. This is the low fan. Therefore, low fan is blue.
Whenever the high fan is on, contact 4 is made. This is the high fan.
Whenever anything is on, contact 6 is on. This is used for the occilator motor.
Whenever the air conditioner is enabled, contact 8 is on.
I can see the yellow wire attached to contact 8 (upper right) is wired to a box that has the temperature probe attached to it. That is, obviously, the thermostatic switch. Another yellow wire connects into the wiring harness connector.
This is simpler than I expected. There are no transformers, relays, or controller things here. It simply switches 120V through to the dirt simple four wire interface with the top unit, not coincidentally exactly like the schematic - only now I know what the output pins mean!
low fan - blue
high fan - black
compressor - yellow
white - neutral
The goal we want is for the fan to be switched by the thermostat. Right now, only the compressor is switched by the thermostat. So, in order to make this do what I want, I should switch the entire power through the thermostat.
consideration: will this put too much power through the thermostat contacts? - The main consumer of power in this air conditioner is the compressor - and its switched through the thing. Adding 20-40% power to it is probably going to be well within spec. I don't think that will be a problem.
Consideration: Will switching the whole unit on the thermostat reduce functionality? - Not really. It will change the operational procedure of using the fan - you'll have to crank the thermostat all the way down to super cold to get it to reliably blow, and it won't blow at all once it gets cold enough. I believe this is an acceptable compromise, I won't be using it when its that cold anyway!
So I see no reason why I can't connect this differently.
Step 5: Connect compressor to switch.
I removed the yellow wire that jumpers between the switch and the thermostat.
Then I disconnected the yellow wire that comes from the wiring harness/connector to the thermostatic switch and connected it to pin 8 on the switch, where the jumper wire used to be.
Step 6: connect thermostat to switch
I used the removed yellow jumper wire to connect the thermostat to pin 7 on the switch. It was closer, and my multimeter told me it was a direct connection inside the switch.
Step 8: connect power to thermostat
I removed the black wire from pin one and connected it to the other connection on the thermostat.
Which makes it look like this:
Step 9: Reassemble
Reconnect wiring harnesses and connect screws and get everything back to where it was.
Step 10: Bezel in place
Turn the thermostat all the way to its warmest setting, and power up the unit. Turn on AC low - high - fan high - fan low - all these settings should produce exactly no response.
But don't panic, its not borked!
turn the thermostat knob down... down... down... until *click* - the thermostat switch activates, and - The unit comes on!
Presto-chango, you now have a thermostatically controlled fan.
However, when the AC Low and AC High selections are chosen, the fan blows continually, and the compressor cycles on and off. That is adequate to the task of cooling the RV - but its noisy. I hate the noise enough when its cooling. But to hear it when its not? Unacceptable. So, I decided to mod it so that the thermostatic control also controls the blower motor.
Mission: Make the blower motor thermostatic.
Tools: My favorite power driver by Makita, an extension, and a #2 phillips bit
Step 1: Disconnect the power.
Step 2: Remove the bezel to get at the wiring.
Step 3: open the wiring boxes. Mine has two - the smaller is the 'Do Yourself' power connection box, and the larger is the wiring box that contains the actual guts.
I removed most of the screws, then found there was one sneakily concealed kind of behind the connection box. Here's my driver getting at it with an extension.
Step 4: Inspect your wiring.
So what have we here? Contact 1 is obviously the power, the black wire that comes from the connection box.
Referring between this photo and the chart printed on the box.
contact 1 is obviously the power.
whenever the low fan is on, contact 2 is made. This is the low fan. Therefore, low fan is blue.
Whenever the high fan is on, contact 4 is made. This is the high fan.
Whenever anything is on, contact 6 is on. This is used for the occilator motor.
Whenever the air conditioner is enabled, contact 8 is on.
I can see the yellow wire attached to contact 8 (upper right) is wired to a box that has the temperature probe attached to it. That is, obviously, the thermostatic switch. Another yellow wire connects into the wiring harness connector.
This is simpler than I expected. There are no transformers, relays, or controller things here. It simply switches 120V through to the dirt simple four wire interface with the top unit, not coincidentally exactly like the schematic - only now I know what the output pins mean!
low fan - blue
high fan - black
compressor - yellow
white - neutral
The goal we want is for the fan to be switched by the thermostat. Right now, only the compressor is switched by the thermostat. So, in order to make this do what I want, I should switch the entire power through the thermostat.
consideration: will this put too much power through the thermostat contacts? - The main consumer of power in this air conditioner is the compressor - and its switched through the thing. Adding 20-40% power to it is probably going to be well within spec. I don't think that will be a problem.
Consideration: Will switching the whole unit on the thermostat reduce functionality? - Not really. It will change the operational procedure of using the fan - you'll have to crank the thermostat all the way down to super cold to get it to reliably blow, and it won't blow at all once it gets cold enough. I believe this is an acceptable compromise, I won't be using it when its that cold anyway!
So I see no reason why I can't connect this differently.
Step 5: Connect compressor to switch.
I removed the yellow wire that jumpers between the switch and the thermostat.
Then I disconnected the yellow wire that comes from the wiring harness/connector to the thermostatic switch and connected it to pin 8 on the switch, where the jumper wire used to be.
Step 6: connect thermostat to switch
I used the removed yellow jumper wire to connect the thermostat to pin 7 on the switch. It was closer, and my multimeter told me it was a direct connection inside the switch.
Step 8: connect power to thermostat
I removed the black wire from pin one and connected it to the other connection on the thermostat.
Which makes it look like this:
Step 9: Reassemble
Reconnect wiring harnesses and connect screws and get everything back to where it was.
Step 10: Bezel in place
Turn the thermostat all the way to its warmest setting, and power up the unit. Turn on AC low - high - fan high - fan low - all these settings should produce exactly no response.
But don't panic, its not borked!
turn the thermostat knob down... down... down... until *click* - the thermostat switch activates, and - The unit comes on!
Presto-chango, you now have a thermostatically controlled fan.