M3/Y: AC compressor failure (Hanon vs Denso, replacement and recharge)

Summary

Model 3/Y has an electric A/C compressor (early 3: a separate compressor without heat pump; from late 2020 the compressor is integrated with the heat pump and Octovalve). There are two manufacturers: Hanon Systems (Korea) and Denso (Japan). On "pre-2021" cars Hanon makes noise and dies more often; Denso from later batches is quieter, but failures of 2020+ heat-pump compressors are also widespread (US replacement bills of $3,800–4,200).

Failure symptoms

• Loud hum/howl when turning on the AC (can be heard from outside).
• Doesn't cool at +25°C with a charged system.
• In Service Mode the compressor RPM hits the ceiling at 11,000 RPM and stays there; per community observations, Tesla later lowered that ceiling via firmware, and the parts nomenclature confirms it indirectly: both "DENSO 8k" and "DENSO 11k no speed limit" appear in it.
• When commanded "AC ON": relay click, hum, then immediate shutoff (overheat/overcurrent protection).
• Errors HVAC_a043 / a044 / a155, "Climate system unable to cool cabin".

What to do

1. Don't go straight to compressor replacement. First, diagnostics:
   • Check the refrigerant level (often the problem is solved by a recharge for $50–80, not far from ЭлектроЭра in Minsk).
   • Clean the condenser and radiator of debris (see separate article). A clogged condenser → overheat → compressor scoring.
   • Read errors via Service Mode → Thermal.
2. If in config the car "sees" the compressor but RPM "hangs at 11,000", on early firmwares it helps to lower the limit to 8,000 RPM in software (per community observations, Tesla itself did the same later via updates).
3. If the compressor is noisy, replace it. Before replacement, flush the loop, otherwise metal swarf will kill the new compressor in a week.

Hanon vs Denso

When replacing with Denso you must write the compressor type via the touchscreen (or Toolbox): Thermal → Actions → Thermal Configurations.

R1234yf vs R134a

• M3/Y and all Tesla with heat pump come from the factory on R1234yf (eco-friendly, mandatory in EU since 2017).
• In Belarus R1234yf is 5–10x more expensive than R134a: $80–150 for an M3 recharge (730 g; pre-refresh ~650 g) vs $20–40 on R134a; the Y holds ~990–1020 g, so a recharge comes out roughly 1.5x more expensive.
• Technically interchangeable with an empty system. R134a recharge is possible and works, but:
  • You need to fully evacuate the loop, blow out and drain old oil residues.
  • Cooling efficiency changes (R134a at the same pressures is colder → can "ice" the evaporator, and with the heat pump running there are nuances).
  • On some firmwares the refrigerant type is written in config: Tesla sees this and sometimes changes operation logic. On M3/Y pre-2021 it is usually informative, compressor logic is identical.
• What veterans say: on older M3 / S / X (without heat pump) the R1234yf → R134a transition is safe and works. On heat-pump cars (M3/Y 2021+, Refresh S/X) better stay on R1234yf.

Warning: if the shop vented R1234yf into the air without your consent and recharged with R134a, that is direct damage: $60–100 of R1234yf could have been resold to AC technicians.

What it costs in Belarus

Parts:

• R1234yf recharge: $80–150.
• R134a recharge (after conversion): $20–40.
• Used Hanon compressor (from a wrecked car): $250–400.
• Used Denso (heat pump): $400–600.
• New Hanon (Chinese OEM/aftermarket): $400–600.
• New Denso: $700–900.
• Dealer assembly: $1 100–1 400.

Labor (Minsk, ≈$50/h):

• Diagnostics + top-up: $50–100.
• Compressor replacement + loop flush + recharge: $200–350 (4–6 hours).
• Programming/configuration in Toolbox: $50–100.

Total: $350–1 800 depending on used/new and scope of work.

DIY notes

• Don't vent old R1234yf into the air: AC technicians buy it back at $50–80 for a full system.
• After flushing, hoses must be clean or filled with POE oil (dielectric). Mixing residues of mineral oil with PAG/POE kills the new compressor.
• For "Hanon with hum" it helps to lower max RPM to 8,000 via MCAN commands (if you have Toolbox / opentesla).
• Before installing the new compressor, weigh the old one and the new one: the new often has excess oil (drain it down to the weight of the old).
• During replacement, fit new O-rings and pull a new vacuum of at least 30 minutes (per manual).

Community experience

From the TESLA owner's group BELARUS chat, analysis of 400,000 messages.

What owners say:

1. R1234yf and R134a are interchangeable with an empty system. The Tesla compressor sticker explicitly lists compatibility with both.
2. On "Hanon with hum" they lowered RPM from 11,000 to 8,000 in software; Tesla itself later fixed this via firmware.
3. The compressor from a 23–24 year car costs ~$800–900 new, and the old one sells for $500–600 (if alive).
4. Smell from the AC comes from the cabin filter and the evaporator, not from the compressor. Cured by filter replacement + cabin ozonation.
5. Refrigerant case: a shop vented 1234 without consent and refilled with 134, and the owner lost 300 rubles for nothing. Control what is being filled.
6. Often the cause is a damaged AC condenser after a crash (even a minor one) rather than the compressor. After replacing the radiator and recharging, the error disappears.

Who reported the issue: Danilius, user1072490676, Yurgen, Андрей, Дмитрий

Who found the fix: Алексей, Алексей Николайчик, fl, Nick, firago, Dmitry D, Zverski

Discussion in Telegram: #646, #785, #3753, #15779, #15782, #15787, #16993

Links

• Compressor (Heat Pump) Remove and Replace (Tesla Service Manual): https://service.tesla.com/docs/Model3/ServiceManual/en-us/GUID-53AA41C0-EC55-403C-BADC-82DCAB9F381E.html
• A/C Compressor + Supermanifold (Heat Pump): https://service.tesla.com/docs/Model3/ServiceManual/en-us/GUID-3F469D2E-A32F-404C-A997-8CCBE1B68318.html
• A/C Refrigerant Recovery and Recharge: https://service.tesla.com/docs/ModelS/ServiceManual/en-us/GUID-57985953-D8E1-4B77-9AA4-9FE0BB458078.html
• Heat Pump Compressor Failure Guide (Motronix): https://motronix.net/blog/tesla-heat-pump-compressor-failure-model-3-y-guide/
• AC Compressor failed (TMC price discussion): https://teslamotorsclub.com/tmc/threads/a-c-compressor-finally-failed-but-3400.113478/
• HVAC compressor bracket replacement video M3/Y: https://www.youtube.com/watch?v=zDJN_30PtTQ