Heat pump in extreme cold -20F

[data003]

So I was driving through some extreme cold pockets this morning -15 to -20F, and I noticed:
1. The truck was blowing cold air
2. The heat pump was not running

I had the heat set to 75, because any lower than that and the truck fogs up really bad with 4 people in it. 2025 Flash with max tow.

When I entered a warmer area, -5 to 0F, the heat pump started and the heat worked again.

So my questions are… what are the limits of the heat pump? Is this documented anywhere? Is there no backup PTC heater for extreme cold?

Thanks!

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[The Weatherman]

I don’t have the specific answers to your questions, but I do have experience with heat pump systems and that behavior is par for the technology. They are very inefficient at those temps. A quick google search will give the answer to the question about the resistance heating.

 

[Tired Lizard]

Just looking thru a 2024 F-150 service manual.
(I don't own a Lightning)

I don't see PTC heaters, only reference to High Voltage Cabin Coolant Heater.

I don't see temperature specs besides:
Electrified Drivetrain Cooling - Electric. - 2024 F-150
NOTE: Coolant temperature will vary with ambient temperature and load. Temperatures shown are for ambient temperature of 25°C (77°F).
Red arrows indicate a temperature approximately 70°C (158°F). Brown arrows indicate a temperature below 70°C (158°F).
Orange arrows indicate a temperature of approximately 40°C (104°F). Blue arrows indicate a temperature below 40° C (104°F).

Heater Circuit
The heater circuit uses a cabin coolant heater and a vapor injected heat pump water cooled condenser (VIHP WCC) to heat coolant that is transferred to the cabin through a heater core.
This circuit also passes through the high voltage battery coolant diverter valve to allow this circuit to be combined with the high voltage battery circuit for battery heating.

Climate Control System - General Information - 2024 F-150
Climate Control System - Electric, Vehicles With: Dual Automatic Temperature Control (DATC)

Cabin Coolant Heater.
The cabin heater circuit provides warm coolant to the heater core to warm the passenger compartment.
A SOBDMC controlled cabin coolant heater warms the coolant.
The upper temperature limit for the cabin heater circuit is 80°C (176°F).
The cabin coolant heater reports the coolant temperature exiting the heater to the SOBDMC through the LIN circuit.
The SOBDMC relays the temperature information to the PCM through the FD-CAN.
Even though the vapor injection heat pump system is more efficient in its ability to provide heat, additional heating is sometimes required (for example in extreme low ambient temperature conditions or during a warm-up phase).
To provide this heat, the system uses the high voltage cabin coolant heater.
The high voltage cabin coolant heater provides heat directly to the coolant circuit.

Max Trailer Tow.

9 Cabin coolant heater
10 Vapor injected heat pump (VIHP) water cooled condensor (WCC)
11 Cabin coolant heater inlet hose
12 Vapor injected heat pump (VIHP) water cooled condensor (WCC) inlet hose
13 Cabin heater coolant pump
14 Front coolant pump inlet hose
23 Coolant expansion tank
24 Heater core
25 High voltage battery coolant diverter valve
26 High voltage battery coolant coolers

 

[chriserx]

As was stated, it is a known limitation for a heat pump, that being said, there does seem to be a heater core and PTC heater also, what I haven't seen clarified is whether the heat pump heats the coolant for heating the cab or a more direct means like it would for cooling the cab. This matters because if it's the latter, it would explain your issue, the PTC must take up the slack and it would take time to heat the coolant to a comfortable level from that temperature.

 

[data003]

Just looking thru a 2024 F-150 service manual.
(I don't own a Lightning)

I don't see PTC heaters, only reference to High Voltage Cabin Coolant Heater.

I don't see temperature specs besides:
Electrified Drivetrain Cooling - Electric. - 2024 F-150
NOTE: Coolant temperature will vary with ambient temperature and load. Temperatures shown are for ambient temperature of 25°C (77°F).
Red arrows indicate a temperature approximately 70°C (158°F). Brown arrows indicate a temperature below 70°C (158°F).
Orange arrows indicate a temperature of approximately 40°C (104°F). Blue arrows indicate a temperature below 40° C (104°F).

Heater Circuit
The heater circuit uses a cabin coolant heater and a vapor injected heat pump water cooled condenser (VIHP WCC) to heat coolant that is transferred to the cabin through a heater core.
This circuit also passes through the high voltage battery coolant diverter valve to allow this circuit to be combined with the high voltage battery circuit for battery heating.

Climate Control System - General Information - 2024 F-150
Climate Control System - Electric, Vehicles With: Dual Automatic Temperature Control (DATC)

Cabin Coolant Heater.
The cabin heater circuit provides warm coolant to the heater core to warm the passenger compartment.
A SOBDMC controlled cabin coolant heater warms the coolant.
The upper temperature limit for the cabin heater circuit is 80°C (176°F).
The cabin coolant heater reports the coolant temperature exiting the heater to the SOBDMC through the LIN circuit.
The SOBDMC relays the temperature information to the PCM through the FD-CAN.
Even though the vapor injection heat pump system is more efficient in its ability to provide heat, additional heating is sometimes required (for example in extreme low ambient temperature conditions or during a warm-up phase).
To provide this heat, the system uses the high voltage cabin coolant heater.
The high voltage cabin coolant heater provides heat directly to the coolant circuit.

Max Trailer Tow.

9 Cabin coolant heater
10 Vapor injected heat pump (VIHP) water cooled condensor (WCC)
11 Cabin coolant heater inlet hose
12 Vapor injected heat pump (VIHP) water cooled condensor (WCC) inlet hose
13 Cabin heater coolant pump
14 Front coolant pump inlet hose
23 Coolant expansion tank
24 Heater core
25 High voltage battery coolant diverter valve
26 High voltage battery coolant coolers

Thank you! Definitely sounds like it has a method of heating the cabin without the heat pump. I wonder why mine wasn’t working.

 

[TaxmanHog]

#9 the aka the PTC is supposed to kick in only when heating demand exceeds the capacity of the VIHP system and boosting the HVB temperatures simultaneously.

 

[Firn]

A few members have had issues with the PTC heater on the older trucks. I'm unsure if there is a way to test it. We do have PIDs for the heater power from the older trucks, I'm going to guess they are the same on the newer trucks. its possible an obd adapter and an app would show you if its working.

 

[WXman]

I have a '25 Flash also. Mine rolled off the line just a couple of months before they stopped making Lightning trucks, so it has the latest and greatest hardware onboard. My heater assembly failed prior to 5,000 miles and had to be replaced. From day 1 the interior would randomly fog up with HVAC set to "Auto" and temp 72-74 degrees. It still does that. However, I haven't yet had my heat pump totally stop blowing warm air. Then again it hasn't been -20 here. About 0 to 5 degrees F is the coldest this truck has seen so far. Might go colder tonight. Overall though, I've never been impressed with the HVAC system in this truck.

 

[data003]

I have a '25 Flash also. Mine rolled off the line just a couple of months before they stopped making Lightning trucks, so it has the latest and greatest hardware onboard. My heater assembly failed prior to 5,000 miles and had to be replaced. From day 1 the interior would randomly fog up with HVAC set to "Auto" and temp 72-74 degrees. It still does that. However, I haven't yet had my heat pump totally stop blowing warm air. Then again it hasn't been -20 here. About 0 to 5 degrees F is the coldest this truck has seen so far. Might go colder tonight. Overall though, I've never been impressed with the HVAC system in this truck.

Interesting, was fogging the primary symptom or did something else occur that made you think the heater failed?

 

[TaxmanHog]

@Tired Lizard THANK YOU for pulling the data & graphics above, I guess I need to sign into PTS and do some more exploring to better understand the landscape of the Lightnings thermal management system, that is both old & new systems.

 

[WXman]

Interesting, was fogging the primary symptom or did something else occur that made you think the heater failed?

No, when the heater assembly failed I got a "Service Vehicle Soon" warning on the dash every day, along with the dreaded wrench icon on the dash. I will say though, the dealership was able to get parts in 48 hours and I was only without the truck for 4 days total.

Apparently this was very common on early Lightning trucks, and people had assumed it was cured by 2025 but that isn't the case.

 

[RLXXI]

Found this.

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