code: public function setTargetTemperatures($temp_low, $temp_high, $serial_number = NULL) {
          $serial_number = $this->getDefaultSerial($serial_number);
          $temp_low = $this->temperatureInCelsius($temp_low, $serial_number);
          $temp_high = $this->temperatureInCelsius($temp_high, $serial_number);
          $data = json_encode(array('target_change_pending' => TRUE, 'target_temperature_low' => $temp_low, 'target_temperature_high' => $temp_high));
          return $this->doPOST("/v2/put/shared." . $serial_number, $data);
      }
docs: Change the thermostat target temperatures, when the thermostat is using a range.
  
  @param float  $temp_low      Target low temperature.
  @param float  $temp_high     Target high temperature.
  @param string $serial_number The thermostat serial number. Defaults to the first device of the account.
  
  @return stdClass|bool The object returned by the API call, or FALSE on error.