Heat pump compressor short cycling

[Sam T]

Hey all,

After 3 months of owning a Tesla Y 2023 I’ve been really struggling with the HVAC energy usage.

After talking with the service technicians at Tesla the first time they convinced me there’s nothing wrong, but there’s definitely something wrong.

A different service centre here in Sydney has looked at it and showed me another Tesla Y service menu where the compressor short cycles too, so I walked away thinking it’s normal. But it’s just not.

The compressor short cycles, as in, it turns off and on again repeatedly, sometimes 3 times a minute, sometimes once every few minutes.

This makes the cabin temperature fluctuate and feels uncomfortable, uses excessive energy and puts abnormal wear on the compressor.

Maybe this is how they’re designed, I don’t know, this is why I’m here, to learn about this and figure it out.

As far as I’m aware, there is not a single compressor on the planet designed to short cycle and that would normally indicate a problem with the system, such as ice building up on the condenser, tripping a safety mechanism to turn the compressor off until it’s safe to run again.

I’ve watched more than a few vids from HVAC school and read so many articles but without tools, experience and more research I’m still a bit lost on the subject.

Can a few people please chime in and take a look at your service menu, under refrigerant system, and tell me if your compressor is turning off and on again repeatedly?

Or does anyone have any clue what’s going on?

There is a low voltage battery error within the service menu, maybe that’s related to the problem?

 

[Sam T]

I’ve asked a couple of local mechanics and they say it’s definitely a problem, but Tesla says it’s normal.
The service centre ran the HVAC and thermal tests on the car, within the service screen and no problems found, but I noticed the problem only happens on lower fan speeds and not at full blast.

 

[Sam T]

Here it is turning off and on:

 

[FatFalcon]

You're already in service mode. If there were issues causing the compressor to 'short-cycle' they would be showing up in the alerts.

The heat pump is a very complex system which operates differently to a conventional HVAC. The fact that other Ys exhibit the same behavior is pretty much case closed in my opinion.

 

[Sam T]

Hey, thanks for your input. If you could please take the time to bring up your service screen and show me your compressor doing the same thing I would be very grateful

 

[Pianewman]

THread drift? A low-voltage battery error can cause erratic electrical system function. Did the SC address the low-voltage error?

 

[Sam T]

That does make sense to me. The battery gives an under voltage error for about 20mins at a time. The SC said because the error doesn’t come up on the normal screen then it won’t be addressed.
You think I should focus on getting the low voltage battery replaced?

 

[Pianewman]

Which battery do you have?

 

[Sam T]

It’s lithium ion, if it were lead acid I’d gladly test it with another battery but alas.

I’ve never seen it go over 80% in the service menu, but it might just maintain that voltage I’m not sure.

 

[DownshiftDre]

Hi again Sam T.

What is your outside temperature and your setpoint temperature when this is occurring. I have stared many time at my heat pump screen in service mode and have never seen it cycle like that.

The reason I am asking of your outside and setpoint temps is wondering if this cycling happens when the outside temperature and setpoint temp are too close so the system doesn’t need to have the heat pump running continuously where even the minimum heat pump speed is too much cooling/heating for continuous need.

Could you run a test where you put your setpoint to the below and observe operation.
1. Max Heat on Auto
2. Max Cool on Auto
3. Equal to outside temp with recirc off and Auto On
4. Equal to outside temp with recirc on and Auto On

 

[DownshiftDre]

I just watched the video and definitely seems weird. I thought the cycling was like 30 sec on and 30 seconds off but I see the cycling is like momentary 0 RPM for barely a second then back on again. That doesn’t seem right (but I am not Tesla). If if needs less heat/cool you would think it can throttle back from the 1600RPM as there is plenty of range to go down to still. I have seen 800rpm sustained continuously.

Your pump is running at 1600rpm. I wonder what the suction temperatures should be for that condition. But then again, if it’s a problem, it would more of a glitch input to the heat pump rather than heat pump performance itself.

Have you also tried to do the two Thermal Tests in the service menu? I assume Tesla did already but doesn’t hurt to watch and see what yours does. Edit: They did run it.

 

[DownshiftDre]

Also can you pull up this low voltage alert and see if it is old or constantly occurring. It should show set/trigger/reset conditions as well. Could be related or unrelated.

 

[DownshiftDre]

Do you have any scan my Tesla or other thing operating in line that could be messing CAN communications?

 

[Sam T]

Hi again Sam T.

What is your outside temperature and your setpoint temperature when this is occurring. I have stared many time at my heat pump screen in service mode and have never seen it cycle like that.

The reason I am asking of your outside and setpoint temps is wondering if this cycling happens when the outside temperature and setpoint temp are too close so the system doesn’t need to have the heat pump running continuously where even the minimum heat pump speed is too much cooling/heating for continuous need.

Could you run a test where you put your setpoint to the below and observe operation.
1. Max Heat on Auto
2. Max Cool on Auto
3. Equal to outside temp with recirc off and Auto On
4. Equal to outside temp with recirc on and Auto On

Hey hey,

Thanks for replying and helping me here.

I’ve tested multiple different scenarios with the same thought process, it short cycles at any temperature set point and any outside temperature, whether it reaches the set temperature or not. It doesn’t seem to correlate with set point temperature, but I did think this for a while.

The only correlation I’ve noticed is when the liquid line and discharge line temperature gets within 1 degree it turns off momentarily while still blowing air.

If the outside air is very hot, the air blowing inside will be warm for a moment when the compressor is off, then it will blow colder than the set point as if the system is trying to compensate, then warm again when the compressor cycles off. Every minute or so. It’s very frustrating.

I’ve never seen the compressor run lower than 1600rpm, are you sure you’ve seen yours run lower?

The low voltage error msg is there fairly often, it clears itself so I’m not sure exactly how many times it’s been there, but I’ve seen it at least 5 times in 3 months.

I don’t have the scan my Tesla tool, I’ve removed the large filter under the bonnet to inspect the duct and filter but everything there looks good.

Every now and then the climate works well, the air blowing is consistent, no whooshing sound of the freon moving from the chiller and the energy consumption greatly improves and exceeds the rated energy consumption. This can last several hours until I get out of the car and the problem returns when I start again.

But I’ll do what you requested, give me a moment.

 

[DownshiftDre]

See 3 pics

-Temperature Setpoint matching outside temperature (76F) around 800-900RPM.

-Setpoint Max Cool (60F) Around 3800RPM.

-Setpoint Max Heat (HI) Almost 7000RPM.

Not once did the heat pump go to 0 RPM but definitely different valves open/close for different configurations.

Are you saying even max cool or max heat, your pump still cycles?

 

[FatFalcon]

This thread is exactly why Tesla doesn't want people looking at service mode.

 

[Sam T]

Hey thanks for your help.

1. Max Heat on Auto (heating)
Rpm: very slow ramp up to 5700rpm
61C delivered
Compressor loud
Compressor didn’t turn off

2. Max Cool on Auto (cooling)
Quick to get to 1800rpm
Compressor quiet
Some interior valves changed and compressor up to 3500rpm
Compressor 1800rpm-2600
Compressor quiet
6C deivered
Low voltage error and red screen saying pull over immediately, getting out of vehicle may solve problem (accelerator power supply UV)
Compressor starts to short cycle from now about once per minute

3. Equal to outside temp with recirc off and Auto On (low)
Compressor trying to maintain 1600rpm
Short cycling more often
Compressor quiet
7C delivered (outside temp 19C)

4. Equal to outside temp with recirc on and Auto On (low)
Same as above 3.
Temperature delivered 6C
Compressor cycles more often (30sec)

Notes: Rear fan off, only middle section selected. New code regarding accelerator pedal

 

[Sam T]

 

[DownshiftDre]

This thread is exactly why Tesla doesn't want people looking at service mode.

I like to think the other way around. This issue is exactly why we look at service mode.

 

[DownshiftDre]

Hey thanks for your help.

1. Max Heat on Auto (heating)
Rpm: very slow ramp up to 5700rpm
61C delivered
Compressor loud
Compressor didn’t turn off

2. Max Cool on Auto (cooling)
Quick to get to 1800rpm
Compressor quiet
Some interior valves changed and compressor up to 3500rpm
Compressor 1800rpm-2600
Compressor quiet
6C deivered
Low voltage error and red screen saying pull over immediately, getting out of vehicle may solve problem (accelerator power supply UV)
Compressor starts to short cycle from now about once per minute

3. Equal to outside temp with recirc off and Auto On (low)
Compressor trying to maintain 1600rpm
Short cycling more often
Compressor quiet
7C delivered (outside temp 19C)

4. Equal to outside temp with recirc on and Auto On (low)
Same as above 3.
Temperature delivered 6C
Compressor cycles more often (30sec)

Notes: Rear fan off, only middle section selected. New code regarding accelerator pedal

That undervoltage and then the heat pump cycling is interesting. At least you now have reason to get them to address that. Your numbers for heat pump performance seem fine but the reset/glitches does not sound normal, unless you are in some predefined heating/cooling zone by Tesla that requires that cycling by design. Doubt it. Max cooling definitely shouldn’t cycle heat pump.