diff --git a/homeassistant/components/climate/nest.py b/homeassistant/components/climate/nest.py
index 3b550c43368..b4492821b1f 100644
--- a/homeassistant/components/climate/nest.py
+++ b/homeassistant/components/climate/nest.py
@@ -10,7 +10,7 @@ import voluptuous as vol
 
 from homeassistant.components.nest import DATA_NEST
 from homeassistant.components.climate import (
-    STATE_AUTO, STATE_COOL, STATE_HEAT, ClimateDevice,
+    STATE_AUTO, STATE_COOL, STATE_HEAT, STATE_ECO, ClimateDevice,
     PLATFORM_SCHEMA, ATTR_TARGET_TEMP_HIGH, ATTR_TARGET_TEMP_LOW,
     ATTR_TEMPERATURE, SUPPORT_TARGET_TEMPERATURE,
     SUPPORT_TARGET_TEMPERATURE_HIGH, SUPPORT_TARGET_TEMPERATURE_LOW,
@@ -27,8 +27,7 @@ PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
         vol.All(vol.Coerce(int), vol.Range(min=1)),
 })
 
-STATE_ECO = 'eco'
-STATE_HEAT_COOL = 'heat-cool'
+NEST_MODE_HEAT_COOL = 'heat-cool'
 
 SUPPORT_FLAGS = (SUPPORT_TARGET_TEMPERATURE | SUPPORT_TARGET_TEMPERATURE_HIGH |
                  SUPPORT_TARGET_TEMPERATURE_LOW | SUPPORT_OPERATION_MODE |
@@ -118,14 +117,14 @@ class NestThermostat(ClimateDevice):
         """Return current operation ie. heat, cool, idle."""
         if self._mode in [STATE_HEAT, STATE_COOL, STATE_OFF, STATE_ECO]:
             return self._mode
-        elif self._mode == STATE_HEAT_COOL:
+        elif self._mode == NEST_MODE_HEAT_COOL:
             return STATE_AUTO
         return STATE_UNKNOWN
 
     @property
     def target_temperature(self):
         """Return the temperature we try to reach."""
-        if self._mode != STATE_HEAT_COOL and not self.is_away_mode_on:
+        if self._mode != NEST_MODE_HEAT_COOL and not self.is_away_mode_on:
             return self._target_temperature
         return None
 
@@ -136,7 +135,7 @@ class NestThermostat(ClimateDevice):
                 self._eco_temperature[0]:
             # eco_temperature is always a low, high tuple
             return self._eco_temperature[0]
-        if self._mode == STATE_HEAT_COOL:
+        if self._mode == NEST_MODE_HEAT_COOL:
             return self._target_temperature[0]
         return None
 
@@ -147,7 +146,7 @@ class NestThermostat(ClimateDevice):
                 self._eco_temperature[1]:
             # eco_temperature is always a low, high tuple
             return self._eco_temperature[1]
-        if self._mode == STATE_HEAT_COOL:
+        if self._mode == NEST_MODE_HEAT_COOL:
             return self._target_temperature[1]
         return None
 
@@ -160,7 +159,7 @@ class NestThermostat(ClimateDevice):
         """Set new target temperature."""
         target_temp_low = kwargs.get(ATTR_TARGET_TEMP_LOW)
         target_temp_high = kwargs.get(ATTR_TARGET_TEMP_HIGH)
-        if self._mode == STATE_HEAT_COOL:
+        if self._mode == NEST_MODE_HEAT_COOL:
             if target_temp_low is not None and target_temp_high is not None:
                 temp = (target_temp_low, target_temp_high)
         else:
@@ -173,7 +172,7 @@ class NestThermostat(ClimateDevice):
         if operation_mode in [STATE_HEAT, STATE_COOL, STATE_OFF, STATE_ECO]:
             device_mode = operation_mode
         elif operation_mode == STATE_AUTO:
-            device_mode = STATE_HEAT_COOL
+            device_mode = NEST_MODE_HEAT_COOL
         self.device.mode = device_mode
 
     @property
diff --git a/homeassistant/components/google_assistant/const.py b/homeassistant/components/google_assistant/const.py
index fc250c4b655..0483f424ca3 100644
--- a/homeassistant/components/google_assistant/const.py
+++ b/homeassistant/components/google_assistant/const.py
@@ -18,7 +18,8 @@ DEFAULT_EXPOSE_BY_DEFAULT = True
 DEFAULT_EXPOSED_DOMAINS = [
     'switch', 'light', 'group', 'media_player', 'fan', 'cover', 'climate'
 ]
-CLIMATE_SUPPORTED_MODES = {'heat', 'cool', 'off', 'on', 'heatcool'}
+CLIMATE_MODE_HEATCOOL = 'heatcool'
+CLIMATE_SUPPORTED_MODES = {'heat', 'cool', 'off', 'on', CLIMATE_MODE_HEATCOOL}
 
 PREFIX_TRAITS = 'action.devices.traits.'
 TRAIT_ONOFF = PREFIX_TRAITS + 'OnOff'
diff --git a/homeassistant/components/google_assistant/smart_home.py b/homeassistant/components/google_assistant/smart_home.py
index e2ad609a007..d8e9f668c8e 100644
--- a/homeassistant/components/google_assistant/smart_home.py
+++ b/homeassistant/components/google_assistant/smart_home.py
@@ -33,7 +33,7 @@ from .const import (
     TRAIT_ONOFF, TRAIT_BRIGHTNESS, TRAIT_COLOR_TEMP,
     TRAIT_RGB_COLOR, TRAIT_SCENE, TRAIT_TEMPERATURE_SETTING,
     TYPE_LIGHT, TYPE_SCENE, TYPE_SWITCH, TYPE_THERMOSTAT,
-    CONF_ALIASES, CLIMATE_SUPPORTED_MODES
+    CONF_ALIASES, CLIMATE_SUPPORTED_MODES, CLIMATE_MODE_HEATCOOL
 )
 
 HANDLERS = Registry()
@@ -147,12 +147,15 @@ def entity_to_device(entity: Entity, config: Config, units: UnitSystem):
                                 entity.attributes.get(light.ATTR_MIN_MIREDS))))
 
     if entity.domain == climate.DOMAIN:
-        modes = ','.join(
-            m.lower() for m in entity.attributes.get(
-                climate.ATTR_OPERATION_LIST, [])
-            if m.lower() in CLIMATE_SUPPORTED_MODES)
+        modes = []
+        for mode in entity.attributes.get(climate.ATTR_OPERATION_LIST, []):
+            if mode in CLIMATE_SUPPORTED_MODES:
+                modes.append(mode)
+            elif mode == climate.STATE_AUTO:
+                modes.append(CLIMATE_MODE_HEATCOOL)
+
         device['attributes'] = {
-            'availableThermostatModes': modes,
+            'availableThermostatModes': ','.join(modes),
             'thermostatTemperatureUnit':
             'F' if units.temperature_unit == TEMP_FAHRENHEIT else 'C',
         }
@@ -323,9 +326,9 @@ def determine_service(
     # special climate handling
     if domain == climate.DOMAIN:
         if command == COMMAND_THERMOSTAT_TEMPERATURE_SETPOINT:
-            service_data['temperature'] = units.temperature(
-                params.get('thermostatTemperatureSetpoint', 25),
-                TEMP_CELSIUS)
+            service_data['temperature'] = \
+                units.temperature(
+                    params['thermostatTemperatureSetpoint'], TEMP_CELSIUS)
             return (climate.SERVICE_SET_TEMPERATURE, service_data)
         if command == COMMAND_THERMOSTAT_TEMPERATURE_SET_RANGE:
             service_data['target_temp_high'] = units.temperature(
@@ -336,8 +339,12 @@ def determine_service(
                 TEMP_CELSIUS)
             return (climate.SERVICE_SET_TEMPERATURE, service_data)
         if command == COMMAND_THERMOSTAT_SET_MODE:
-            service_data['operation_mode'] = params.get(
-                'thermostatMode', 'off')
+            mode = params['thermostatMode']
+
+            if mode == CLIMATE_MODE_HEATCOOL:
+                mode = climate.STATE_AUTO
+
+            service_data['operation_mode'] = mode
             return (climate.SERVICE_SET_OPERATION_MODE, service_data)
 
     if command == COMMAND_BRIGHTNESS:
diff --git a/tests/components/google_assistant/__init__.py b/tests/components/google_assistant/__init__.py
index db075fb6789..022cf852b88 100644
--- a/tests/components/google_assistant/__init__.py
+++ b/tests/components/google_assistant/__init__.py
@@ -211,7 +211,7 @@ DEMO_DEVICES = [{
     'type': 'action.devices.types.THERMOSTAT',
     'willReportState': False,
     'attributes': {
-        'availableThermostatModes': 'heat,cool,off',
+        'availableThermostatModes': 'heat,cool,heatcool,off',
         'thermostatTemperatureUnit': 'C',
     },
 }, {