air conditioning question

[okc666]

Looks ng for a definitive answer on this,

I was told for longest time not to leave the a/c on when shutting off the engine because it isn't good to have it on at startup. Is there any truth to this or is it harmless to do this? Thanks

[Chris]

From what i was told a while back, its more electrical load and having the clutch engaged was harder on the starter. But even if you leave it on when you shut off, you can always turn it off before you turn the key all the way to "start"

[Jsdirt]

I would agree with that. In addition to the load of cranking over the engine,your now adding a compressor that has to start from a dead stop. Not only are you placing an additional load on the starter, but the belt that drives it as well. If there was ever a time that a belt would break at high miles, that would be it.

 

I would think since everything is computer controlled these days that all the newer trucks would lock out the compressor for a few seconds after startup ... but I don't have an answer for that.

[Chris]

Time to get a test light, multimeter, and a friend to figure it out

[Doug_Scott]

No need for anything more than a friend. Simply open the hood, ask him/her to start engine, and watch/listen for compressor to engage. I for one have never heard that claim. And to be honest, I put zero faith into it. I would think that if trying to start the engine with the compressor engaged is a shock to the system, what is it called when the compressor gets engaged while engine is running at 4k rpm and the compressor is at 0 rpm? And to make it even worse, that system of starting the compressor with the engine running at speed occurs hundreds of times on a long drive. Having the compressor engage during very low engine speed at start up sounds like child's play when compared to what happens to it later on in the drive.

 

Old wives tale in my opinion.

[Jsdirt]

I think the slow turning of the compressor (while cranking) would abuse the belt more than engaging at speed (due to the momentum instantly overcoming the load). No concrete proof of that - that's just how I see it. I've been wrong before ...

 

It certainly places more load on the starter, unnecessarily too.

[okc666]

All interesting opinions, thanks. Hopefully we get a few more opinions.

[02suburbanZ71]

Just to be safe turn it off before shutting the truck off and turning it on like me. But sometimes i forget the aux climate

[Jsdirt]

Now that I think of it, I leave mine in AUTO constantly, set at 72°. From spring to fall I leave the A/C on (snowflake symbol lit). Whenever I start it up, a couple seconds later I hear the compressor kick on. Apparently it is indeed computer controlled. So, leaving it on in the newer ones is a non-issue.

[02suburbanZ71]

When its super super cold and i turn my heat on i get a really loud high pitch noise like its really bad. Only happened a couple times is this the compressor kicking in?

[Jsdirt]

Blower motor bearings. This has been a GM staple of high mileage vehicles since the late 70's.

 

[00Silverado4x4]

Blower motor bearings. This has been a GM staple of high mileage vehicles since the late 70's.

 

Sounds about right to me.

[Doug_Scott]

When its super super cold and i turn my heat on i get a really loud high pitch noise like its really bad. Only happened a couple times is this the compressor kicking in?

 

If temp is below freezing my 2010 will not engage the compressor regardless of what I select.

[02suburbanZ71]

Must be the blower motor

[Doug_Scott]

Now that I think of it, I leave mine in AUTO constantly, set at 72°. From spring to fall I leave the A/C on (snowflake symbol lit). Whenever I start it up, a couple seconds later I hear the compressor kick on. Apparently it is indeed computer controlled. So, leaving it on in the newer ones is a non-issue.

 

Personally, I have never seen a compressor or clutch fail due to being engaged when the vehicle started, or have any belt or starter issues due to it either. Given that likely 90 to 95% of new cars sold in the last 15 years have a/c, if this was an issue, it would have shown up by now. I also think that engaging of the clutch at high rpm would cause more damage anyways.