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RPM drop with AC on causes stalling

msg on Mon September 01, 2014 8:51 AM User is offline

Year: 1963
Make: Chevy
Model: Chevy II
Engine Size: 194
Refrigerant Type: r12
Ambient Temp: 87
Country of Origin: United States

Finally got my original 1963 AC system running. Just put the compressor belt on added R12 last night.
The rpms are running at around 600 and once the AC is turned on it drops in RPMS to the point that if I hit the accelerator it stalls.
Should I have increased the idle speed at the carb (single barrel rochester) or is there something else to adjust/correct?

GM Tech on Mon September 01, 2014 9:17 AM User is offline

Yes

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

GM Tech on Mon September 01, 2014 9:17 AM User is offline

Yes

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

wptski on Mon September 01, 2014 12:44 PM User is offline

Don't you have an adjustable solenoid at the carb to override the idle setting when the A/C in ON?

mk378 on Mon September 01, 2014 4:42 PM User is offline

It's a 1963 model, may not be that elaborate. One could be added of course.

msg on Wed September 03, 2014 7:17 PM User is offline

I have learned that I have a Carb Airator (Engine Idle Compensator) that is connected to the manifold that is supposed to prevent stalling when the ac is on. I have taken it apart and cleaned it out and reinstalled. Afterward I did adjust the idle and when AC is not on its at 840 rpms at idle in park, and when AC is on it drops to 600 rpm. Seems high for base idle but that part doesnt seem to be doing that good.

Here is a link for a pic of the part

http://s387.photobucket.com/user/msgdesign/media/ac%20system/IMG_3584_zpsf375d09d.jpg.html][IMG]http://i387.photobucket.com/albums/oo320/msgdesign/ac%20system/IMG_3584_zpsf375d09d.jpg

bohica2xo on Wed September 17, 2014 2:10 AM User is offline

That air leak is an aftermarket work around for hot idle compensation. It has no connection to the A/C system, and will not magically raise your idle when the compressor is on. It is nothing but a thermostatic vacuum leak, and is likely causing the problem to begin with.

I would not want anything like that installed with the brake booster line in any case.

Your tip-in stall points to a lean condition - and a vacuum leak will just make that worse.

Is this an automatic transmission car?

You need to check the ignition timing, and the idle mixture setting. Too lean or not enough advance will make it stall with the added load.

Is the A/C system an aftermarket unit?

B



-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Cussboy on Wed September 17, 2014 1:42 PM User is offline

I have an aftermarket carburetor in my 1988 B2200 truck, and it does not have any idle compensation for AC. Since I live in Arizona, and use the AC 10 months a year, I just set the idle to about 950rpm with AC off, and when the AC is on it drops about 200 rpm, works fine. And that's a 4-cylinder truck, about 85 hp, Sanden 708 compressor, R-12.

Viceroy on Wed October 01, 2014 12:51 AM User is offline

A proper AC compensator should be installed so that the solenoid plunger pushes on the throttle arm when the AC is engaged. That's how it was done on factory AC carb cars and trucks. It's a fool-proof method, and many times is adjustable as well, so you get it right where you need it.

msg on Sun October 05, 2014 10:02 AM User is offline

Quote
Originally posted by: bohica2xo
That air leak is an aftermarket work around for hot idle compensation. It has no connection to the A/C system, and will not magically raise your idle when the compressor is on. It is nothing but a thermostatic vacuum leak, and is likely causing the problem to begin with.



I would not want anything like that installed with the brake booster line in any case.



Your tip-in stall points to a lean condition - and a vacuum leak will just make that worse.



Is this an automatic transmission car?



You need to check the ignition timing, and the idle mixture setting. Too lean or not enough advance will make it stall with the added load.



Is the A/C system an aftermarket unit?



B

msg on Sun October 05, 2014 10:48 AM User is offline

Quote
Originally posted by: bohica2xo


Is this an automatic transmission car?


Yes it is an automatic, powerglide

Quote
You need to check the ignition timing, and the idle mixture setting. Too lean or not enough advance will make it stall with the added load.


Since posting the original issue I have tried out a few things and it has improved.
I found a NOS carb-airator pretty cheap and tried it out and it did at least remedy the vac leak on the previous one that was constantly happening whether the ac was on or not.
I checked the timing and set it to 10 degrees, it was off the timing tab completely with all of the idle adjusting I did at the carb
I reset the idle mix screw by turning the idle mixture screw slowly in a clockwise direction with a screwdriver until it is fully seated but not overtightened to avoid damage, then turned the screw counterclockwise 2-1/2 turns.
Then I hooked up the multimeter and set it to read rpms on a 6cyl and adjusted the idle speed screw until it reached around 900 rpm with the air off.
Then checked the timing and found that each time I adjust the idle speed it affected the timing.
So it took a bit of back and forth to get the timing at 10 with the rpms at around 900.
Locked it all down and started testing the ac off and on and here is where things are.

970 rpm in Park with no air
730 rpm in Park with air on
530 rpm in Drive with air on
650 rpm in Drive with no air


It doesnt stall out anymore and rides great but I am fairly new to tinklering on cars and I wonder if these are normal rpm ranges.


Quote
Is the A/C system an aftermarket unit?


This is the original factory ac system that was on this very same vehicle since 63.
I had sent off the original A6 compressor, receiver/dryer and thermal expansion valve to have it all checked and rebuilt by Classic Auto Air.
The condenser was reconditioned by a local radiator shop.
The evaporator I had flushed and pressure tested myself and found no leaks

bohica2xo on Mon October 06, 2014 12:51 PM User is offline

Your numbers look pretty good. You kind of got there from the back side, but you are close.

I pulled a 30+ year old book off my shelf & looked:

194 CID I6

550 RPM +/- 25 rpm Curb Idle

8 Degrees BTDC ignition timing

Curb Idle is set in DRIVE, with the A/C ON, Headlamps ON

Ignition Timing is set at Curb Idle, vacuum advance disconnected & plugged (no vacuum leaks)


Given that you set the timing & mixture in neutral, it may be a bit off - but drive ability trumps a couple of degrees of timing on pre-1965 cars. You may not be able to run the full 8 degrees without pinging on today's gasoline. If it drives ok, record where you are at before you change anything. Small changes from the base tune may help - or not.

Idle fuel mixture in those years was not based on emissions. The book instruction for pre-1965 194's was:

Adjust idle mixture for highest steady vacuum and smoothest idle at Curb Idle RPM. Re adjust Curb Idle if necessary.

B



-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

msg on Mon October 06, 2014 2:15 PM User is offline

Thanks for looking that up B!
I had tried the 8 degrees previously and got a bit of a bog happening. Usually around 10 to 12 it behaves better.
I may try out a few adjustments after I record where things are.
The next thing I am dealing with is a concern about some potential R12 leakage at the evap. I posted a new thread on it though. Hopefully its a false alarm with the detector I have but something tells me to try and inject some UV dye into the system somehow and look at things after.

mk378 on Mon October 06, 2014 5:54 PM User is offline

Make sure your vacuum advance system works by pulling a vacuum on the distributor diaphragm part, it should not leak and applied vacuum should make it advance. This advance is important for off-idle performance. Without it you have to advance the base timing to make the car able to go anyhere, and then cut the air way back to reduce the idle speed with the timing advanced. That makes it hard to get a consistent idle.

Edited: Mon October 06, 2014 at 5:56 PM by mk378

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