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Discussion Starter · #1 ·
Has anyone noticed a musty smell from AC at start up for 5 to 10 seconds or so? Never had this in any AC car or last 2 Vettes, wondering if drain is plugged.Trip to work is 1.5 miles and then parked inside all day. Don't want to do the Dealer thing it's working now!

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Technical Service Bulletin
A/C - Odor Emission in Hot Weather
May, 2001

Subject: Air Conditioning Odor (Install Kit)

Models: 1993-2002 Passenger Cars, 1993-2002 Light & Medium Duty Trucks

This bulletin is being revised to update the model years, service procedure, parts information and to add the GEO and Medium Duty models. Please discard Corporate Bulletin Number 99-01-39-004 (Section 01 - HVAC).


Some customers may comment on odors emitted from the air conditioning system, primarily at start-up in hot humid climates.


This odor may be the result of microbial growth on the evaporator core. When the blower motor fan is turned on, the microbial growth may release an unpleasant, musty odor into the passenger compartment. There are several other possible sources of a musty odor in a vehicle. A common source is a water leak. Follow the Service Manual procedure for identifying and correcting water leaks if other odor sources are found. The procedure contained in this bulletin is only applicable if the source of the odor has already been determined to be the HVAC module.


To remove odors of this type, it is necessary to eliminate the microbial growth and prevent its reoccurrence. To accomplish this, the following steps must be completed:

# Apply evaporator core Cooling Coil Coating (Aerosol 6 oz), P/N 12377951 (AC Delco(R) 15-102) (in Canada, use P/N 10953503) or Cooling Coil Coating Kit with Extension Nozzle, P/N 12346391 (AC Delco(R) 10-120). Refills are available for the Cooling Coil Coating Kit with Extension Nozzle, P/N 12346391 (AC Delco(R) 10-120). Refer to the chart below.
# Install the Electronic Evaporator Dryer, P/N 12497910 (AC Delco(R) 15-5876).

Important: The Cooling Coil Coatings listed above are the only GM approved products for the disinfection and long-term control of evaporator microbial growth. The Cooling Coil Coating will disinfect the evaporator core and help inhibit the growth of future mold and mildew.

The Electronic Evaporator Dryer will activate when the ambient temperature near the module is above 16°C (60°F) when the vehicle is started up. Approximately 30 minutes after the vehicle has been turned off, the blower will activate for 10 seconds every 10 minutes for 2 hours unless the vehicle is restarted. If a restart occurs, the Electronic Evaporator Dryer module will reset automatically. This on/off blower activation will dry the evaporator core and case reducing the chance of reoccurring A/C odor. The Electronic Evaporator Dryer is self fused and has a battery rundown protection feature that inactivates the dryer if voltage drops below 12.5 volts.

Service Procedure

# Visually inspect the air conditioning evaporator drain hose for obstructions and/or working condition.
# The cooling coil coating fluid must be applied to a dry evaporator core. Apply coil coating fluid as described in the instructions supplied with the kit. In some instances, the blower motor resistor can be removed for this spraying operation. If used, the opening can be taped over and the nozzle inserted through a hole in the tape. The kit instructions identify a drilling procedure to apply the coating fluid. When using this type of procedure, care must be taken to avoid evaporator damage and any holes must be properly sealed. Some coating fluid may overflow from the drain hose.

Important: When installing the Electric Evaporator Module, you MUST use the included electrical splice connectors to ensure a splice.
# Complete detailed installation instructions and wire connectors are supplied with the Electronic Evaporator Dryer. The ground wire should be attached to a body ground source. If any other wire splicing procedures are needed, follow the wire repair procedures in the Electrical sub-section of Body & Accessories in the appropriate Service Manual. I f required, the evaporator dryer can be installed underhood away from extreme heat conditions (i.e. exhaust manifolds) and/or water splash areas. In all cases, the evaporator dryer module must be secured with a Velcro(R) strip (not included in the kit), or you may use the integral hooks to utilize tie straps. Using a Velcro(R) strip is preferred as the use of the integral hooks may cause rattles.
# When the installation procedure is complete and power is supplied, the module will self-test. Thirty seconds after power is supplied, the high blower speed will be activated 3 times (for 2 seconds per cycle). When the test has run, install the Electronic Evaporator Dryer label on the blower motor case in a visible area.

Parts Information

Parts are currently available from GMSPO.
Part Number Description
(AC Delco 15-102) Cooling Coil Coating
(Aersol 6 oz)
(AC Delco 15-120) Cooling Coil Coating Kit w/Extension Nozzle
(AC Delco 15-121) Refill for Cooling Coil Coating Kit
(AC Delco 15-5876) Electronic Evaporator Dryer Module Kit

Warranty Information

Labor Operation Description Labor Time
D3316 Apply Cooling Coil Coating/Install Electronic Evaporator Dryer 0.8 hr
For vehicles repaired under warranty, use the table as shown.

1,311 Posts
I have a Z16 and noticed the same thing. Anyone have any ideas about this?
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