A/C and starting

Does the compressor put much of a load on the engine at startup?
Lately I've taken to turning the A/C off after I shutdown the engine
and giving it a couple of seconds of run time before I turn the A/C
back on. Am I being silly? If it only saves a couple of percent, yes
I am.
--

- dillon I am not invalid

"Iran wants nukes? North Korea wants nukes?
I'm sure we can give them some. Or the Navy."

- former B52 wing commander

 

The compressor clutch will not engage until the engine is running, so the
position of the A/C switch makes no difference on startup.

You're better to turn the A/C off a couple of miles from home, not right at
shutoff. Allowing the evaporator a few minutes to come to ambient
temperature (with the blower fan remaining on) will help dry up the
condensation that eventually leads to that "stinky socks" smell.

 

I go beyond that. I usually don't turn on AC until the engine has
warmed up (at least a minute).

 

Most cars don't energize the compressor until the key is back in the "run"
position after starting. Now if your engine is flaky & doesn't start up
smoothly, it might have a hard time with the extra load hitting it shortly
after starting, but there is no extra load while starting.

 

Thanks. More for the stinky socks advice. I HATE that with a
passion.

And if you have a turbo, make sure it idles for at least 30 seconds,
unless you have some sort of additional pressure oiling system.
--

- dillon I am not invalid

"Iran wants nukes? North Korea wants nukes?
I'm sure we can give them some. Or the Navy."

- former B52 wing commander

 

pressure isn't the issue with a turbo, it's "heat soak". heat from the
turbine conducts back to the shaft and the bearings after it's switched
off and cooks the oil in it. allowing the turbine to cool by idling
[some trucks used to spec three minutes] before switch off mitigates
this. using an oil that can take the heat [synthetics] is strongly
recommended.

 

I think what Dillon means is the sort of system that maintains oil flow
through the turbo for X-minutes after engine shutdown. Such a system is
meant to prevent the oil in the turbo from being heated to the point of
coking.

 

Yeah. Since I don't race "tin tops" any more, I can't remember the
name of the system that did that. It would store up about a litre of
oil in a little resivor and then use either air pressure (via a
piston) or an electric pump to push the oil into the system. They
also had one that primed the system at startup.

With three pump dry sump systems, I don't worry about that, much.
--

- dillon I am not invalid

"Iran wants nukes? North Korea wants nukes?
I'm sure we can give them some. Or the Navy."

- former B52 wing commander