It seems that I am experiencing some slight hesitation in my 1991 RS 305 TBI since I just got A/C working. The compressor is working fine, and all I did was throw some new R12 in there. Bear in mind, I have not used this A/C for three years. It wasnt until this summer that I couldn't handle the heat, so I went and got it fixed. I know the A/C requires fuel, but I feel that the car is hesitating during acceleration, especially when the engine is cold.

-Is it possible the compressor is 'stealing' fuel from my TBI in essence not giving enough fuel for the intake?

-Is fuel directly used by the compressor to activate my A/C?

I need some answers. Maybe its not a problem at all. Some advice or input would be useful though.

Thanks,
Eric

 

A/C compressors have nothing to do with a fuel system. The compressor runs off the belt, in turn makes it harder for your motor to turn, thus causing a fuel comsumption if that.
That is your hesitation, theres a load on the motor that you never noticed before.

 

as stated the a/c causes the engine to work harder while actuated(on). since the engine has to wrk harder that in effect will cause the engine to use a little more gas. that will also result in the car feeling a little more "sluggish".

 

always start your engine with the AC off. makes it so much easier on the engine. You might be starting it with it and making it 3 times harder on the starter.

 

If it's working correctly the compressor clutch is disengaged while starting, so it doesn't put a load on the starter. And the compressor does drag down a TBI 305 quite a bit, if I have it ON and need to pass someone quickly I turn it off.

 

thats one thing i noticed as well. Had a 3.3l cutless cierra with a 4 speed and some other junk, and the a/c didnt bother it one bit. Didnt even notice it was on as far as performance was concerned. With the SC and the junk 170 HP lo3, i could really tell it was on from the parasitic loss that i felt.

 

so d00d your saying its supposed to turn off when starting...... sh*t whats wrong if it dont then? Mine doesn't do that and i have to turn it off when starting the car.

 

then the clutch would probably be seized to the pully, if that can happen. The HVAC controls for the compressor shouldnt have power when the key is turned to the start postition. Even if it still turns, so what... It wont drag it down too much when its going around at like 50 rpm. Lol, not meant in a mean way or anything but your (dunerida's) comment about the compressor directly needing fuel to work jsut brings up a funny image in my head of a little 5HP briggs & stratton engine puttin' away in your engine compartment to run your compressor.

 

oh, an easy way to see if the compressor is spinning is to look and the triangular spring assy. on the clutch. If its spinning, the compressor is engaged. Stationary, its not engaged.

 

Thanks for the tips fellas. I did a little "test" with it today on some residential streets. There is definitely a direct correlation between my TBI and A/C when its turned on. There is a slight hesitation on the accel when it is on, and halls *** when off. I didnt really gun it, but I know its the A/C.

One quick question:

When I commute to San Diego, and am cruising in 5th gear overdrive, you think I'll notice any hesitation? Havent had it on the FWY yet, and I would like to know your thoughts?

 

You should never have any hesitation, the AC will just make the car feel slower, if it hesitates then you will have to look for the problem. Have you done or had a tune-up on it? Make sure the distributor cap and rotor, sparkplugs are good and the o2 senser is pretty new. The timing is critical on the engines too, if it's retarded even a few degree's it will really kill the power, they run better if it's advanced a few degree's from the factory setting of 0, I run mine at 4 deg. advanced and it helps the power and mileage.

 

I have a 94 chevy silverado with the 350.

I ran about 250 miles at night with the ac off, fuek consumption/power was fine.

On the way home (sunday morning) I had the A/C on the whole time. Not only did I notice a bit more of a struggle up the hills, but the mileage was seriously almost cut in half. (BTW i tow a 22ft boat and a camper)

When power and fuel are a concern I definetaly keep it off. Of course I don't know what kind of compressors the cars you guys are building have for the A/C, but mine looks like a hog fit to cool a fridgerator

 

AC makes little difference in MPG on my car, no more than a couple MPG at the most, no way it should cut MPG by half, you must have have been pulling more hills on the way back. And on my 00 Dodge Ram 1500 with the 5.9 engine the AC makes no difference at all, the tach wont even dip any when it's switched on at idle. Now the compressors used back in the 60's,70's and early 80's were gas hogs, it was common to loose a lot of MPG with them on.