Faint smell of burnt antifreeze on engine start in 2002 XLS

[erom43]

I recently developed an odor like burnt antifreeze that occurs when I first start the car, but then it quickly dissappears. It was more prevalent when I was in North Carolina during rainy weather. It doesn't happen every time. Checking under the hood has revealed no obvious leaks of any sort. Also, the coolant level has remained steady.
The car is a 2002 XLS with over 130K on it. There has been recent work done on it including tune up, IAC module replacement and fluid checks and flushes. There has also been a slight loss in gas milage (around 7%) that hopefully is unrelated.
Similar posts have mentioned a possible heater core leak, but I show no dripping on carpets at all. Anyone have a similar problem or suggestion?

[TedL]

Run a pressure test on the cooling system. As part of diagnosing, determine if the smell is coming from inside (heater core) or outside (everything else).

[erom43]

Further diagnosis: FYI. The odor is present merely by turning on the ignition key without starting the engine. It appears to be coming from the AC vent when the fan starts blowing. Again, it dissappears in a few seconds.

[TedL]

Are you certain of the identity of the odor? Burnt coolant is not going to happen unless it's leaking onto the hot exhaust. That's not happening for the first minute or two.

What coolant are you using?

[erom43]

That is a very good point! Burnt coolant is only how I perceived the odor. I could have been swayed by other posts. The odor could be anything. The coolant in the reservoir is red. After smelling the coolant directly, I noticed it has no odor in its natural state.

Assuming the odor is not coolant.....what could cause a stale, musky chemical type odor to eminate with the initial blower activation, and rapidly dissappear? My guess is that something has gotten into, or is leaking into the vent or AC system in very small amounts. Or, it might be something electrical that only happens with the ignition process. Any other ideas?

[TedL]

Stale musky can be the evap needing cleaning. Also, have you changed your cabin air filter recently?

Would you recognize the odor of refrigerant oil? Is your a/c working well?

[erom43]

Cabin air filter was supposedly checked during last workup. AC seems to be running fine, but that could be an illusion because weather is cooling now. I would not recognize the smell of refrigerant oil. AC was checked recently, but evap cleaning is a possibility.

[bobflood]

Check and make sure that the A/C drip tray drain is not plugged. The water that the A/C pulls out of the air condenses on the condensor and drips into a tray that has a drain that comes out underneath the car on the pass side. (That's why you always have a puddle of water underneath the car when you park it in the summer.) If that gets plugged even partially, it could be letting condensate sit in the tray and produce the smell.