Ok here we go. I have a 1998 C280, last week I had the AC filled with freon as it was low. Obviously, there is a small leak. A week later the economy light came on and hasn't gone off. I have been told that it's either the evap sensor or reg. temp. sensor. I bought them from the dealer today. Tomorrow I will replace them. My question is, am I barking up the wrong tree? Also, how much freon is supposed to be in the system? Any input would be greatly appreciated, more than you know.

Thanks,
FA

Also what type of pac oil should I use? I know 150 is the most common, but don't know what I should use.

That's PAG oil. If it's a slow leak, you may not need to add any.

I'm not familiar with your car, but my '96 210 can tell me all of the sensor readings while running. That feature helps to easily point to or eliminate any sensor as the culprit. Try holding the REST button down for five to ten seconds, until the display changes.

oops pag oil, anyway. I did something really stupid. So I assume I need to add the oil too. While playing the reg sensor I loosened it and all of the freon was released. So I assume it should be done also.

Check out my problem a few years ago - http://www.peachparts.com/shopforum/showthread.php?t=86110&highlight=economy+light

Pay particular attention to the reprogramming info on the second page.

Was your refrigerant actually low or maybe the faulty sensor only thought it was?

Len
'99 E300TD 88,000 miles

In that case, you will need to add oil. The big question is how much. Undoubtably, some is still in there, and you don't want too much oil. If you can flush the system and start fresh, you'll know that it's correct.

The correct quantity of refridgerant should be listed on the tag under the hood. I believe that the oil quantity is specified in the climate-control diagnostic manual. If I get a chance, I'll try to look it up.