Classic Retrofit AC- Idle dropping when AC turns on. Replacement Battery?

[jakg104]

Hi Folks,

Got the Classic Retrofit AC running. The car is a 77 with a fresh 3.2 SS motor running PMO Carbs. The Classic Retrofit kit includes 2 condensers as well as Jonny’s upgraded Alternator. New wiring from battery to alternator, etc.

Install has been performed by Rennsport in Sealy, TX.

Here is the issue- With the AC off (blue button), the car idles correctly. As soon as the AC is kicked on, the idle drops quite a bit. Seems like there is a good amount of power draw is what we can assume.

The battery in the car is a regular one that is a few years old.

Question- Would it help to get a higher CCA battery to assist with the power draw?

Any other ideas for why the revs could drop at idle?

Thoughts or suggestions?

Thanks!

Jake G

[Nditiz1]

How much idle drop? I believe there is some. I think without the AC on when car is fully warmed I am around 1100, but when the AC is on around 1000. You do need to set your idle a little higher ~1000 otherwise the compressor when kick off too soon when at a light. Sometimes I will pull the ebrake and bring the revs up to 1400 at a long light so as to not cycle the compressor off. When it does cycle you lose about 10 - 15 degrees of temp from the vent as a result. It takes a lot longer for it to get back to the temp it was at vs the amount of time it increased while at the stop light.

[jakg104]

Originally Posted by Nditiz1

How much idle drop? I believe there is some. I think without the AC on when car is fully warmed I am around 1100, but when the AC is on around 1000. You do need to set your idle a little higher ~1000 otherwise the compressor when kick off too soon when at a light. Sometimes I will pull the ebrake and bring the revs up to 1400 at a long light so as to not cycle the compressor off. When it does cycle you lose about 10 - 15 degrees of temp from the vent as a result. It takes a lot longer for it to get back to the temp it was at vs the amount of time it increased while at the stop light.

Thanks for the response, i appreciate it!
I sadly don't have the drop in number because the tach wasn't working. I'll get the mechanic to read it off the ignition wires so we know.

Good point on raising the revs at idle. I now wish I had installed a hand throttle from an early car on this car to get more control of this.

I remember growing up in India, we used to have this car called Maruti, which was a Suzuki 800 rebranded and built in India. We installed an AC in that car and had to install an idle control that would physically push up on the throttle arm on the carb. The switch was electronic and I still remember it being ingenious because it kept the compressor engaged and kept the car cooling.

I'm now thinking how cool it would be to find something similar. All i came up with was the hand throttle option...

[targa80]

I have an amp and voltage gauge in my car so at idle I raised the rpm’s until the current was no longer negative but was close to zero on the amp gauge. Granted with the ac off my idle is high around 1300 rpm. Since I live in Florida when I start the car the ac comes on and idles around 1100 rpm’s.

[jakg104]

Originally Posted by targa80

I have an amp and voltage gauge in my car so at idle I raised the rpm’s until the current was no longer negative but was close to zero on the amp gauge. Granted with the ac off my idle is high around 1300 rpm. Since I live in Florida when I start the car the ac comes on and idles around 1100 rpm’s.

Ah! Very good point on setting idle WITH AC on. I'm in Houston and can't see any time that AC being off, so I'll pass this onto the mechanic.

Amp/volt gauge- Do you mind sharing which one you have?
Thanks!

[targa80]

Originally Posted by jakg104

Ah! Very good point on setting idle WITH AC on. I'm in Houston and can't see any time that AC being off, so I'll pass this onto the mechanic.

Amp/volt gauge- Do you mind sharing which one you have?
Thanks!

I installed a VDO volt/amp combo.

[jakg104]

Originally Posted by targa80

I installed a VDO volt/amp combo.

Nice! Thanks for sharing!