AC Compressor theory of operation?

[geordi]

Summer is hot, no shock there. But I’m wondering if anyone knows the theory of operation on the non-heat-pump dual AC system in the Model X.

I’m still experiencing higher than expected power usage, with a second MX now that I can compare against - also a dual AC unit 2016, it’s a 6 seater. Highway driving on that one is under 400 wh/mi where mine is STILL consistently closer to 500 wh/mi. Not much difference based on speed. Twice in the last week, I have been cut down to “AC performance reduced” THC_u0016 and the compressor disabled while supercharging. This latest time it almost immediately came up with the u0005 code (vehicle systems being cooled) right after plugging in. When the AC is running, it is FROSTY cold, yet I can’t really hear the compressor running - which says it is possibly at low speed - but the forward fan is SCREAMING all the time even when the temperature is moderate AND the AC fan speed and demand are both very low.
Ju7 in the same unit? Virtual support suggested that they were in the same module, and that the gas would need evacuation to change this (that’s no issue for me) but I don’t want to just throw parts at it.

The car HAS reduced / turned off the compressor when I have the interior temp set warmer (you know how you can tell when the air just seems “stale”) several times, but no errors are presented. Even now, cruising on flat land at 80-85mph with no headwind, the AC is possibly colder than I’d like (it is set at 70 with ambient at 85) and I’m at 500 wh/mi. Something is STILL running continuously / drawing a fair amount of power, and I don’t know where to look.

It isn’t the air suspension - that compressor is unplugged right now b/c of an air leak between the tank and the valve block. The suspension hasn’t leaked down in over 500 miles either which is refreshing!

Just plugged into another supercharger and IMMEDIATELY the AC compressor was cut off (it’s getting dark and the outside temps are somewhat more moderate now) and I got the THC_u0005 systems being cooled message. It didn’t even have time to start heating up from the supercharging before it cut off the AC. The front fan is STILL running full speed, and the compressor is only humming quietly, way less than when the AC is at full demand - pressure is 60 psi on the low side.

 

[EbS-P]

Do you set the passenger temp different than driver?

 

[brainhouston]

X has a very small opening for air to cool off the condenser/radiator compared to the actual condenser size
also 2/3 of condenser has radiator on top
so, for fan to run at full speed all the time it would mean that either louvers are not opening or that opening is clogged up...

 

[geordi]

I do not have a separate temperature set, I am the only one in the vehicle.

On the front with the louvers… I don’t know that I have louvers on a 2016? Part of my forward air dam is uninstalled at the moment but I didn’t remove anything powered. Let me have a look and confirm, but I also plan to be taking the front bin out tomorrow to work on the air suspension (again) after I finally get home from this trip, so I’ll see about pulling the cover from the top and have a good look there. I need to see the rest of the AC lines anyway to see where this sensor might be located, so I’ll look for any blocking and clean that up if I find any. No errors about anything other than an occasional RCCM Actuator error - but no idea what that is referencing yet either. Their error messages really aren’t helpful.

Confirmed - The top of the radiator is clear, and I can see the entire thing. The amount of air coming straight down (b/c the forward dam is in the garage) is most impressive - and NOT steaming hot right now at night, but the fan is at full blast. ScanMyTesla says the cooling target is 100.4 with the cells at 108, and the fan has just calmed down finally, still charging at 34kw

 

[geordi]

Sorry - just noticed that when I edited my first post, apparently my "helpful" ipad decided to eat an entire paragraph and spit up a typo.

The missing part was asking if anyone knows where the fan logic and compressor logic are coming from - either a temperature sensor or a pressure sensor, and whether they are in the same unit. Virtual support suggested that they were in the same module, and that the gas would need evacuation to change this (that’s no issue for me) but I don’t want to just throw parts at it.

I have had an error that only shows in service mode for an RCCM actuator, and when running the thermal test the ONLY fail result is the temperature sensor.

Faffing around with it some more tonight I discovered yet another air suspension line that wasn't holding air - so my repair needed replacement. Did that. Meanwhile in playing with ScanMyTesla, it shows 1kw power usage when the AC is on for the front only. Interior fan below 4. It promptly doubles to 2kw when the rear air is added, also at fan 4. The condenser fan was NOT screaming at this point, and I could hear the compressor hum increase in speed and intensity. Turning either fan up above 4 and the power increases to 3kw and the condenser fan becomes obvious.

So it WOULD seem that the AC is behaving itself right now, when not asking insane amounts of cooling from it or trying to cool a hot battery AND a hot interior while on the surface of the sun. This suggests it either doesn't have enough gas (I don't believe this is the case), enough capacity for the environment (a possibility)... OR the compressor isn't up to the challenge b/c of wear issues. Still have more research to do.

 

[brainhouston]

u would have to look at schematics but i'm pretty sure it has some hvac module
it definitely has temp n pressure sensors somewhere based on my diag screen

Couple of sensors are here:

 

[ShawnA]

Hi @geordi ,

You may want to have your car checked against Service Bulletin SB-16-18-002

This bulletin was specific for 2016 Model X with crappy A/C and crappy cooling at Superchargers.

The condenser tubing was installed on the incorrect condenser ports...
May also have condenser tubing incorrectly touching the front sway bar...

Good luck,

Shawn

 

[geordi]

u would have to look at schematics but i'm pretty sure it has some hvac module
it definitely has temp n pressure sensors somewhere based on my diag screen

View attachment 978355

Couple of sensors are here:

View attachment 978354

Thanks - Looking around in EPC, they have part numbers listed for what I gather is both of those. They are listed as temperature AND pressure sensors for the low and high side. This might be a mislabeling b/c there's no compelling reason to measure the temperature of the refrigerant, and those sensors in your image look like ordinary pressure sensors. It IS normal to monitor both high and low side, and those also look like they are mounted on the normal shrader-equipped ports rather than a fully open port as the virtual service guy suggested.

I have not found any other obvious temperature sensors listed in EPC, so one of these two may be my culprit - and I plan to replace both and see if the conditions improve. The dang thing cut off the compressor AGAIN today in the Florida heat, but this time it did it just while I was driving on the highway and I suspect the system might actually be OVER charged rather than under like they were saying - the VS had said they had an alert for "low pressure" that didn't show on the car's screen, but I didn't have my full gauge set with me to be able to verify anything. I may have to start carrying that until I resolve this.

Hi @geordi ,

You may want to have your car checked against Service Bulletin SB-16-18-002

This bulletin was specific for 2016 Model X with crappy A/C and crappy cooling at Superchargers.

The condenser tubing was installed on the incorrect condenser ports...
May also have condenser tubing incorrectly touching the front sway bar...

Good luck,

Shawn

Thanks for that - I will be looking at that when I pull the cover off. I'm sure that if it is wrong, the service center will HAPPILY fix it for me.... At a cost of $1000 for the work. Their finger seems to have gotten stuck on that price point for everything.

 

[brainhouston]

Thanks - Looking around in EPC, they have part numbers listed for what I gather is both of those. They are listed as temperature AND pressure sensors for the low and high side. This might be a mislabeling b/c there's no compelling reason to measure the temperature of the refrigerant, and those sensors in your image look like ordinary pressure sensors. It IS normal to monitor both high and low side, and those also look like they are mounted on the normal shrader-equipped ports rather than a fully open port as the virtual service guy suggested.

I have not found any other obvious temperature sensors listed in EPC, so one of these two may be my culprit - and I plan to replace both and see if the conditions improve. The dang thing cut off the compressor AGAIN today in the Florida heat, but this time it did it just while I was driving on the highway and I suspect the system might actually be OVER charged rather than under like they were saying - the VS had said they had an alert for "low pressure" that didn't show on the car's screen, but I didn't have my full gauge set with me to be able to verify anything. I may have to start carrying that until I resolve this.

Yes i think its normal to monitor both sides press n temp.
Looks like its dual purpose sensors:

Also totally spaced out, everything is controlled by THC

EPC won't help u much, look at schematics on service.tesla.com

 

[geordi]

Wiring diagrams only do so much - I was looking at EPC b/c I'm visually chasing the lines and looking for what is on them. The reason there is normally no monitoring of the refrigerant temperature is that the temp is dependent on the pressure and the ambient temperature outside the system. Once those two things are known, then the refrigerant performance is predictable and linear. Monitoring refrigerant temperature on both sides of the compressor is somewhat redundant b/c they are monitoring the pressure already. But hey, that's how they are doing it. Since the error I've seen is a temperature one from the thermal tests, swapping these out is a cheap way to know they are good and hopefully solve the problem.

 

[geordi]

Had an interesting afternoon - I swapped out both refrigerant pressure/temperature sensors and recharged the system with the right amount of gas, plus an ounce of POE oil and some dye. I don't think the system is leaking, but JUST to be sure.

The pressure now reads 25 psi on the low side and 200 on the high. The interesting part is I ran another thermal test cycle from service mode and this time it came back with a failure of the evaporator. Not sure what it is reading there, b/c the system seems to be working fine.

 

[MobileClimate]

What’s the evap temp sensor at ?

 

[geordi]

I don't know a way to read the evap temperature sensor, and the location isn't marked on the parts description for the evaporator core.

Do you know a way to scan that sensor specifically? I have ScanMyTesla and an OBDlinkMX.

 

[MobileClimate]

TESLAX app under evap temp raw.. it’s the most important sensor on the ac system because it’s the one sensor that it’s going to use for capacity control of the compressor and how much superheat to adjust on expansion valve

 

[geordi]

Ok, haven’t messed with Tes⸱LAX in a while and that’s actually a pretty good program. The evap raw is 39 degrees, the target is 50, while the outside temperature is pushing 90 (in the sun and not moving). Front and rear AC are both at full power and auto mode.

What should I be seeing if everything is working correctly? Does this seem normal? I am going to monitor as I drive around today.

 

[geordi]

Monitoring while driving and I noticed that it seemed like the compressor would shut off for a moment and the temperature would climb, sometimes at the same time as my XM radio would stop and display the radio ID / seem like it was rebooting. This wasn't always at the same time.

Going to have to mess with Tes-lax a bit more to see if I can monitor the refrigerant sensors and the compressor, and put them all on the same screen.

- This was when the compressor seemed "off" with no obvious reason. Radio did not reboot.

- Baseline while driving and cooling.

Thoughts?

 

[MobileClimate]

The evap temp should be 35F and it should reach it quickly ..with the car off for a few hrs look at all the temps for the vent temps they all should be the same the same as ambient temp if not then you need to figure out which one is not accurate ..if the evap sensor reading is bouncing around i would replace it

Yes the teslax program is great ..one one huge problem with it ...no more updates to LEGACY mx and ms..so the can data could be wrong ..i wish somooe one couold update the legacy dbc file

 

[geordi]

If the target temperature of the evaporator is 50 degrees, why would the coil temp be 35? It WAS 35 when the AC was at full power / LO temp setting and max fan. The two screens from the last post are with the demand setting at 70 degrees, trying to see if it is properly slowing down the compressor to reduce the power demand. I found the extra sensors and updated the page to show *everything* about the HVAC. Once I did that, in looking at it on this last drive I feel like the sensors are behaving, I don't see anything too far out of bounds. I'm in the 5 day demo of the advanced features, what do you mean there aren't any more updates to the files.... Is it worth paying for the 2.x advanced level?

 

[MobileClimate]

Couple things why is the cabin heater at 10%. Didn’t you say the fans were on full power ? 13% you should barley be able to hear that .. you sure the lines at the condenser are not backwards ?
You said it’s a 2016 some had the lines backwards and some came with a compressor that had a internal metal fatigue I would find that service buelltin and make sure that not your car

 

[geordi]

No, the image from Post 18 is with the temperature set at 70°. It makes sense that there would be a little bit of cabin heating at that point but now that I see it is doing that, costing me energy, I might instead leave the temperature down and just control it with fan speed.