2021 Mercedes-Benz AMG GT HVAC Performance Issues

Mercedes-Benz has issued Technical Service Bulletin (TSB) L183.30-P-079850, version 4, dated January 16, 2026, to address common heating, ventilation, and air conditioning (HVAC) performance concerns in all Mercedes-Benz passenger cars, including the 2021 Mercedes-Benz AMG GT. This TSB provides guidance for technicians on diagnosing and documenting HVAC complaints where the AC does not cool effectively, has poor performance, or the heating is insufficient.

This bulletin emphasizes a thorough diagnostic approach given the "many possible root causes" for a degraded Mercedes-Benz AMG GT HVAC performance. It details the necessary steps for technicians to confirm the customer's complaint, perform diagnostic tests, and properly document their findings for warranty claims.

Symptoms

Owners of a 2021 Mercedes-Benz AMG GT may experience one or more of the following HVAC-related symptoms:

• "Body > Air conditioning > Heater > Remains cold"
• "Body > Air conditioning > Heater > Remains warm/hot"
• "Body > Air conditioning > Heater > Insufficient heat output"
• "Body > Air conditioning > Heater > Cold in footwell"
• "Body > Air conditioning > Air conditioning > Insufficient cooling output"
• "Body > Air conditioning > Heater > Malfunction, defrosting"
• "Body > Air conditioning > Heater > Footwell flap cannot be opened/closed"
• "Body > Air conditioning > Air conditioning > Temperature differences"
• "Body > Air conditioning > Air conditioning > Cooling output too high"
• "Body > Air conditioning > Heater > Center air air vent does not close"
• "Body > Air conditioning > Air conditioning > Temperature control not sensitive enough"

Important Warnings for Owners and Technicians

• TSB Applicability: This bulletin (L183.30-P-079850) is not applicable if other specific Mercedes-Benz Li documents already address your concern, or if a fault code or guided test directly points to a root cause.
• Leak Detection Method: When checking for refrigerant leaks, "Forming Gas is the ONLY approved leak test method. (DYE is NOT approved)." This prevents the use of unapproved methods that could potentially cause further issues or invalidate warranty claims.

Diagnosis Overview

Technicians are instructed to follow a detailed diagnostic process to identify the root cause of the Mercedes-Benz AMG GT HVAC performance issues. This includes:

1. Verify Customer Concern: Confirm the reported issue and compare the vehicle's behavior to a similar, properly functioning vehicle to determine if the behavior is normal.
2. Identify Diagnostic Strategy: Determine the appropriate diagnostic strategy and pinpoint the involved components or systems.
3. Perform Relevant Diagnostic Tests: Conduct necessary tests, including recording the amount of recovered refrigerant and comparing it to specified values.
4. Before Repairs Documentation: Record gauge readings (high and low pressure), document any leaks found (in PPM), print XENTRY data for climate control and HV compressor AVs, and take thermometer readings from dash, footwell, and rear vents. Ambient conditions (temperature and humidity) from OCP AVs should also be noted.
5. After Repairs Documentation: Post-repair, technicians must record high and low pressure gauge readings and thermometer readings from all relevant vents to confirm the repair's effectiveness.

Warranty Claim and TIPS Case Submission

For warranty claims and TIPS (Technical Information and Problem Solving) case submissions, a specific "4 level model template.docx" attachment is required. A TIPS case is only necessary if the root cause cannot be identified, or if other Li documents mandate opening a case.

Operation Codes for Diagnostics

Mercedes-Benz provides specific operation codes for technicians to use when documenting diagnostic time related to HVAC concerns:

• 831232: Max 0.5 hours for Cooling Capacity Test.
• 831040: Max 1 hour, only for active diagnosis of a specific fault code.
• 831762: Includes basic leak check.
• 831285: Max 1 hour, only for situations where a leak cannot be found despite extenuating circumstances.

What Owners Should Do

If you are experiencing any of the described Mercedes-Benz AMG GT HVAC performance issues, it is recommended to schedule an appointment with an authorized Mercedes-Benz service center. Technicians will utilize this TSB to accurately diagnose and address the problem, ensuring proper documentation for any potential warranty claims.

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NHTSA ID: 11027751