# Need help understanding details of thermostat wiring scheme

I bought this thermostat to control air circulation, that is using it for cooling purpose. So far I managed to make it work, but I do not fully understand the wiring scheme. I would appreciate help to fully understand the scheme.

In the scheme L is linked to 3 squares where the middle one labelled with "5". The square to the right is connected to the square labelled with "2"? What is the purpose of this connection?

The square to the left of "5" is connected to the square labelled "N" using a dotted line. What is the purpose of this connection?

The model number is RTR-E 6732 https://docs.rs-online.com/8e9b/0900766b800ccc84.pdf

EDIT:

I found another wiring diagram where the unlabelled blocks are lacking (see page 9) https://docs.rs-online.com/ae5d/0900766b81583b25.pdf

• That diagram is very poor as is their technical documentation. My guess is that the '5' block is the main electronic logic but why it has a dashed connection to the N terminal, rather than a solid, I have no idea. The top contact is unlabeled so we don't know what switches it. The '5' to '2' connection is strange. The arrangement of contacts on the right seems to switch on and off the RF (radio frequency?) module and we have no idea what the box with the '<' symbol represents. Weird. Mar 7, 2020 at 9:47
• the line between 5's neighbour and 2 is the board outline not an electrical connection. Mar 7, 2020 at 9:49
• @Transistor The "<" symbol represents the actual thermostat unit..I read it as follows: As long as the temperature is below some value the switch to the left of it is in the position it is now. When temperature is higher than some value the switch is activated Mar 7, 2020 at 9:54
• The box which labelled with "RF" is the thermal acceleration unit. It serves to reduce temperature amplitude. Basically it heats the thermostat unit as such as that it switches earlier therefore reducing temperature amplitudes... Mar 7, 2020 at 9:56
• @Transistor You wrote :"but why it has a dashed connection to the N terminal, rather than a solid," But if there was a connection wouldn't that lead to a short circuit?? Mar 7, 2020 at 9:59

I'm seeing a classic bimetallic thermostat with two control switches and one knob.

I have deleted the outline and colourised it a little.

Terminal 5 connects to the live 240V power

Switch A connects this to terminal 1 when on

Switch C is the bimetallic thermostat and connect terminal 1 to either the hot link or cold link and the anticipator resistor labeled "RF" for some reason (my German isn't very good)

Switch B is the heat/cool selector and connect the output terminal 2 to ether the hot link or the cold link.

B and C work together like a two-way light swicth, so when both heat/cool and the temperature selection are in agreement the and the power switch is on output 2 is live.

• Thanks for your answer. What about the dashed line from 5 to 4? It is present in both schemes Mar 7, 2020 at 10:46
• it's just the boundary of the device, it's not an related to its operation. above I deleted it and used a tint instead. Mar 7, 2020 at 11:14

Your second diagram was a good find and is far superior.

I think @Jasen is correct. The dashed line and the right-angled line between '5' and '2' are the controller board outline. This was neither clear nor consistent.

This diagram also makes it clear that the 'RF' block is an 'Acc' or accelerator. I saw this trick used on the electrical carriage heating on the Dublin Bay Rapid Transit (DART) during commissioning. The wall mounted thermostats were slow to react to rising carriage temperatures and this resulted in slow but wild changes in temperatures. A small resistor was added inside the thermostat housing to accelerate the switching of the bi-metallic strip thermostat. The problem was solved. (Interestingly the heaters were mounted under the seats and, if the thermostat contacts were closed, a blast of heat could be felt during regenerative braking as the line voltage rose from 1500 V nominal to, probably, about 2000 V.)

So ...

• There is no direct connection between '5' and '2'. The connection is via the On/Off switch, S1.
• When switched on the fan runs continuously.
• When below temperature power is fed to the valve if S2 is in position shown. I expect this to heat the room until the thermostat switches.
• If S2 is reversed (cooling) then the valve is off until the temperature exceeds the setpoint.

• -
• Thanks for your answer. What about the dashed line from 5 to 4? It is present in both schemes Mar 7, 2020 at 10:45
• it's just a boundary. Mar 7, 2020 at 11:12
• Think of it as the edge of the circuit board. It's not an electrical circuit connection. All the components inside the box are inside the controller. Mar 7, 2020 at 11:19