Hi, I have searched the forum, but can't find exactly the same symptoms being reported.

I 'think' I finally figured out why my A/C is not working at start up and after the engine cools a bit. At idle, the fan clutch does not engage cool until the engine is 'fully' warmed up. Once the fan is engaged, the A/C cools as expected. Likewise, when the engine is hot and then left off for a while, the fan clutch does not engage until the engine fully heats up again. It seems like the fan clutch should engage anytime the A/C is turned on.

Any thoughts?

Thanks,
VaDreamer

 

You give no clue as to what vehicle you are asking about. If you actually have a fan clutch, it engages based on temperature. Electric fans always turn on when the AC is working.

 

Some fans have a viscous coupling that is sensitive to temp coming through the condenser and radiator and will engage full when the temp is considered hot enough while some have a thermostatic spring that will lock up the fan when temp is hot enough.

From what you describe, it sounds like there is a problem within the A/C system.
Usually the A/C works fine until things warm up , then they come up with problems.
Could you have possibly described the condition incorrectly?

 

Sorry, new to the forum and figuring out how to use it. I typed it up about 4 times and I forgot the important info. it's a 2005 Trailblazer. The fan/clutch is tied to the ECM and apparently is activated that way. Here is a link to the fan on Auto Zone:

Duralast Fan Clutch 922498 (autozone.com)

 

Sorry, new to the forum and figuring out how to use it. I typed it up about 4 times and I forgot the important info. it's a 2005 Trailblazer. The fan/clutch is tied to the ECM and apparently is activated that way. Here is a link to the fan on Auto Zone:

Duralast Fan Clutch 922498 (autozone.com)

 

It sounds like your fan clutch might not be working properly. I am guessing you had to replace the fan clutch that was in your 2005 and you purchased a new one from Autozone - correct?

Well, from all I have read the best choices for replacement fan clutches are Genuine GM/ACDelco, Behr/Mahle, Hayden/Four Seasons, NAPA Temp, or Dorman. Not knowing who makes Duralast is a big "stay away" in my opinion.

You just might want to warrant the fan clutch and get one of the brands I mentioned. Also, fan clutches are less expensive at rockauto.com

Good Luck!

 

I have not replaced anything yet. I am trying to determine exactly what I need to replace, before throwing money at it. The Autozone link was just to show that it has an electrical component. As far as I know, this may all be the original components.

What I know is:

1) the A/C does not cool at idle when the engine temperature drops below 200 degrees and I can stop the fan with my hand.
2) as soon as the engine temp gets above 200ish degrees the A/C will work at idle and I cannot stop the fan with my hand.
3) if the engine is hot and then turned off and cools for a while, the A/C will not work at idle until the temp gets up to 200 degrees.

I read somewhere about a thermistor could be the issue. Don't know where that might be located.

It could also be a bad ECM/PCM.

As far as I can tell it is working correctly after it gets to 200ish degrees. I just don't want to spend money on something that is not broken until I know for sure what is broken.

 

It's not unusual for these trucks to suffer from "AC withdrawal" at idle due to lack of air flow over the condenser. Once the vehicle gets moving and air is flowing over the condenser AC performance will greatly improve.
Have you put a set of AC gauges on the truck to measure the pressures? When you do that you'll need to know the outside air temperature and the relative humidity, as desired pressures will change with different temps and humidity levels.

 

I have not put gauges on it, but when it is sitting still and the engine temperature is below 200 degrees, the fan is freewheeling and the A/C is warm. Still sitting still and the temp gets up to around 200 degrees, the fan is locked and the A/C starts cooling. that tells me that the fan is at least partially the issue.

Honestly, I am contemplating just putting a switch in to lock the fan manually and see if that corrects the issue.

 

You first have to diagnose and not guess what is wrong. Do you have a Digital Multimeter (DMM) and a Coder Reader/Live Data Scanner that will allow you to monitor various engine parameters such as the coolant temperature that is being reported to the ECM by the engine coolant temperature sensor? What Diagnostic Test Codes (DTCs) are present? Do you have a set of AC gauges to read both the high and low side pressures while the engine is running and the AC compressor is engaged?

Until we have data on what the AC pressures are, that the AC clutch is getting 12 V when you say the engine temperature is below 200° F, what if any DTCs are present, then we can guess all day and not come up with an accurate diagnosis. Too many unanswered questions at this point. Based on what you write, your fan clutch sounds like it just might be working properly. Putting a switch in line would only muddy the waters even more as the ECM monitors the electronic fan clutch.

You could be low on refrigerant, have a bad clutch on the AC compressor, a bad AC compressor relay, etc.