I wrote before about temperature drops, and some replied that it is a thermostat and temperature sensor failure. Well its not. Whenever the temperature drops, the AC lights are blinking.
I'am certain that it is an AC problem, I just don't know which part of AC that is failing.
The "room" temperature itself is fine. It is the radiator fan that won't go off when I turn the engine off that is bothering me (besides the incorrect temp gauge)
Anybody got an answer?

The ECT sensor plays into the AC as well. Blinking lights indicate a code in the ECC system which could be in any number of sensors, including the ECT sensor.

I know that there is a code waiting to be read, but it is embarrasing to visit Volvo dealer so many times just to read codes...! Hey it's the Yellow 850 again..!
I didn't replace the thermostat nor the ECT because the temperature back to normal whenever I turn off the AC. Logically the ECT and the thermostat are OK.

Who said you could apply logic to the situation?!?!?!

No, really....it is logical, follow my reasoning; there is a method to my madness.

The only components that can affect your temperature gauge the way that you spoke of are the thermostat, and the engine cooling fan. Your engine cooling fan is a two stage fan, meaning under normal circumstances, it will turn on at the lower speed whenever a certain temperature is reached, or the air conditioning is turned on. Once a certain temperature is reached, AND you turn on the air conditioner, it kicks into the higher speed. Of course as you are heading down the road, at higher speeds, the outside temp sensor will alert the climate control that the front fan is no longer needed, unless this signal is overridden by the ECT. So, really, I guess the problem could be the outside temp sensor for the climate control, but...

didn't you also say something about running rich? or am I confusing you with someone else I attempted to answer? Either way, both of these parts are cheap...both of these parts could do what you are saying...the ball is in your court.

Chris

Yes I'm following your madness, but can you explain why the temp working normally when the AC is not in use???? If the ECT or Thermostat are bad, then the temp should not work at all circumstances.
It is not the price concerned me, but going back and forth to a Volvo shop is no fun at all. I would rather do it me self.
Running rich?? definitely not me. I would not be writing this if I'm rich.

Well, unfortunately, you're gonna have to go back to the dealer, or an independent with the means of reading and clearing the climate control codes. Since it only happens with the AC on, and neither you nor your car are running rich, opt for the outside temperature sensor, particularly if you have an ambient temperature reading in your gauges that doesn't seem to be giving you an accurate reading. These go bad all the time since a) they are in a vulnerable spot and b) they tend to come loose from there home and bang around next to your radiator. Should you still continue to have the problem, then replace the ECT and thermostat (which, really, if it is still original and hasn't failed yet, it's about to).

Once the problem is solved with either one or two of the components, visit the dealer or independent to clear your codes.

Oh...off the subject...I love that laffy taffy color on the 850!

I know that there is a code waiting to be read, but it is embarrasing to visit Volvo dealer so many times just to read codes...! Hey it's the Yellow 850 again..!
I didn't replace the thermostat nor the ECT because the temperature back to normal whenever I turn off the AC. Logically the ECT and the thermostat are OK.

did you replace the t-stat and ECT sensor? If so, then you can assume is an AC problem.

If the t-stat fails in the open position, the engine does not reach normal operating temp, then the temp gauge will drop down when you cruise, sometimes you get CEL on.

AC lights blinking, means there are codes stored in the ECU, generic OBD II code readers won't read these, only the volvo toolscan.
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'88 240, '92 745, '98 v70 John, Tampa Bay