Understanding how the interior heating system works

FWIW your photo shows the A/C as being On. (Blue border around the power icon, and the physical button lit up orange/amber).

Edit: I see what you mean now - the A/C icon is Off.

Is some confusion here about what people mean by turning A/C on?

There are three separate controls that can be referred to as "the A/C switch", and its not always clear which one is meant without seeing a picture

• the physical button with fan symbol on the left below the screen
• the power "button" on the screen upper right
• the A/C "button" on the screen

All three need to be on for automatic temperature control (heating and cooling).

I don't think the screen button labelled A/C needs to be on for heating to work, but assume the other two should be.

siteguru said:

Do the models with a heat pump also still have a PTC heater? (The UK models have no heat pump but do have a PTC heater ... and after I got the latest Infotainment and HVAC updates my HVAC controls have been nigh on perfect).

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PTC=?

siteguru said:

Do the models with a heat pump also still have a PTC heater? (The UK models have no heat pump but do have a PTC heater ... and after I got the latest Infotainment and HVAC updates my HVAC controls have been nigh on perfect).

Click to expand...

I don't actually understand what you mean, are you referring to MG in general or just MG4 models?
My MG4 Trophy LR has a heat pump, I cant speak for other MG models.

As far as is known no UK MG4 has a heat pump. Please can you confirm by photo/documentation that yours is a UK model with a heat pump. My Trophy LR does not have a heat pump.

Joningy said:

I don't actually understand what you mean, are you referring to MG in general or just MG4 models?
My MG4 Trophy LR has a heat pump, I cant speak for other MG models.

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This is the MG4 board, so I'll let you work it out.

As per above, no UK MG4 model (not even the ER I believe) comes with a heat pump. MG UK decided that we didn't need it here so as to save on cost (hence improve profit margin).

The power button and the physical button both control whether the HVAC is active.
An active HVAC consists of A/C to cool/dehumidify the air and a PTC heater to warm it, plus the controls for fan speed, vents and air intake/recirculation.
Switching the A/C off does not affect everything else.
The physical button is a quick way to set the HVAC off and recirculate air. Should be temporary (tunnel) or to save electricity in extreme circumstances.
The A/C and PTC heaters can work at a reduced load if ECO is enabled in the HVAC control screen.
Once you press AUTO, everything (except ECO and temperature) is set to automatic control.
If you touch the fan speed control after pressing AUTO, all controls will stay on Auto except the fan speed.
If you then touch the vent direction buttons , all other controls will stay on auto except the vent direction and fan speed.
and so on.

The latest updates on the SE have made the target temperature more in line with reality (it was offset by 3C on previous versions)
The Auto setting was also favouring the face vents over the wind screen and feet vents therefore causing the cabin to get too cold and then too hot on a cycle.
Now I believe they have adjusted the logic so it uses the face vents only when higher degree of cooling or heating is required, and to maintain the temperature it uses windscreen and feet only.

siteguru said:

This is the MG4 board, so I'll let you work it out.

As per above, no UK MG4 model (not even the ER I believe) comes with a heat pump. MG UK decided that we didn't need it here so as to save on cost (hence improve profit margin)

Click to expand...

I've said it before, and I'll say it again - my UK MG4 Trophy ER has a heat pump.

I don't know whether it has a PTC heater as well as the heat pump.

The type certificate says it was built September 2023, and I bought it new through an MG dealer last year.

After earlier comments on this thread, I removed the black plastic cover under the bonnet to take a closer look. All the visible components are those shown on pages 243-244 of the Service Repair Manual (aka Refit and Remove Manual), which are different from the parts of the non-heat pump a/c on pages 241-242.

I only found out that it has a heat pump when investigating whether to buy a third-party frunk. There are two types on the market, and I discovered that the ones for cars without a heat pump won't fit my car.

That's interesting info re. the ER. But @Joningy's Trophy LR will almost certainly not have a heat pump - if it's a UK-spec car.

ReintjeWA said:

Air conditioning is more than just a way to cool the air. It conditions the air to whatever you set it to, even in ICE cars the air will heat up quicker using your aircon.

I haven’t tried this because of always have the aircon on and no real need for heating since I got the car, but I imagine you are correct in thinking the car doesn’t generate heat by itself, or at least not enough, and so needs the aircon to accomplish this.

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Set mine to 28 degrees C, it’s really around 23 true temperature.

melvinolotus said:

Set mine to 28 degrees, it’s really around 23 true temperature

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Same 28°C, mine has to be set to at least 27°C to get any heat out at all, less than that and it just blows cold.

Of course these figures are for before the firmware update that basically corrects the figures (so the temperature setting then needs to be about what you want it to be; what a concept).

Yup - I set mine to 21°C and Auto, and it works really well now.

MDWMG said:

I've said it before, and I'll say it again - my UK MG4 Trophy ER has a heat pump.

I don't know whether it has a PTC heater as well as the heat pump.

The type certificate says it was built September 2023, and I bought it new through an MG dealer last year.

After earlier comments on this thread, I removed the black plastic cover under the bonnet to take a closer look. All the visible components are those shown on pages 243-244 of the Service Repair Manual (aka Refit and Remove Manual), which are different from the parts of the non-heat pump a/c on pages 241-242.

I only found out that it has a heat pump when investigating whether to buy a third-party frunk. There are two types on the market, and I discovered that the ones for cars without a heat pump won't fit my car.

Click to expand...

Most EVs with a heat pump also have a PTC heater. The heating capacity of a PTC heater is much higher in comparison with a heat pump. When the cabin is at (or almost) at the desired temperature, the heat pump takes over.
That said, that's how most EVs work.. As we all know the MG4 is not like most EVs.

Am I right in thinking an air source heat pump is basically an AC system in reverse ?

Kithmo said:

Am I right in thinking an air source heat pump is basically an AC system in reverse ?

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correct

So basically in our MG cars we do have a heat pump set up to cool, like a fridge. A heat pump set up to provide heat is very efficient capable of producing more energy (heat) than it consumes. Cooling is the reverse, inefficient. Surely we just need the ability to run it in reverse mode, no need for another heat pump? (my ice maker can reverse as can air to air heat pumps). Am I misunderstanding?

melvinolotus said:

Set mine to 28 degrees C, it’s really around 23 true temperature.

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Exactly my strategy.

Janda2 said:

So basically in our MG cars we do have a heat pump set up to cool, like a fridge. A heat pump set up to provide heat is very efficient capable of producing more energy (heat) than it consumes. Cooling is the reverse, inefficient. Surely we just need the ability to run it in reverse mode, no need for another heat pump? (my ice maker can reverse as can air to air heat pumps). Am I misunderstanding?

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Not in Britain we don't.