2014 GL450 Front AC Condensate Drain


New member
Vienna, VA, USA
Strange situation with the front AC unit on our 2014 GL450.

Had a temporary malfunction of the front AC unit where it would not blow out any air. This is the second time its happened in 2 years. When driving through a hard rain storm, the front AC unit stopped blowing. It stopped blowing out any air at all regardless of the HVAC settings.

Throughout the incident, the rear AC continued to function normally and there were no warning indicators of a malfunction. On many MB vehicles the red LEDs in the temp control will flash if the freon is low and/or there is a malfunction detected by the system. No flashing LEDs or any other signs of an issue. But the front AC would not blow out any air, even when on MAX AC.

It appeared as though the evaporator coil had frozen over. Parked the GL with the engine running and there was no condensate draining from the front of the car. Turned off the car and waited - after a few mins the condensate started to trickle out of the condensate drain. Pulled the front end up on a high curb and crawled underneath with the GL turned off again. The condensate was draining from the drain tube but not very fast (the drain tube exits inside the tranny tunnel on the passengers side).

After a few more minutes, the condensate continued to trickle out. We were on the highway on a 500 mile trip and had to get it fixed. So I got on the phone and started calling. Talked to 2 different MB dealers - neither one were much help (it was late on a Friday). Stopped by a third dealer in Washington, PA. They were nice, but the service techs had already departed for the day. Got a call back from a MB serve tech in DC and I walked him through the troubleshooting I'd performed. He confirmed my suspicions that the front condensate drain is probably partially clogged on the inside. The partial blockage, whatever it is, was keeping the condensate from draining a the normal rate and when driving through the hard rain storm the extra moisture being extracted from the AC was too much to drain. Once the condensate backed up and touched the evaporator coil, the coil quickly froze up.

This has only happened one other time that we've owned the GL and it was while driving through a hard rainstorm on the eastern shore of MD. Same exact situation happened with no air coming out of the front AC unit. In both cases, when we let the car set for 20 minutes, the condensate drained out enough so that when we started the car again the front AC resumed normal operation.

Has anyone else experienced this before?

Has anyone ever cleaned out the condensate tray in the front AC unit on a X-166 GL450?

Appreciate any info available.