AC= significant power loss

I have a 95 caprice with a 4.3L V8. When i turn the ac on the car really throttles down and has a significant loss of power/acceleration. I try to only turn it on while cruising on the highway. If the cruise and ac are on while at highway speeds it will be fine for a few seconds then be hesitent for a split second and this just repeats over and over. When the car is cold first thing in the morning i can turn the ac on with no problem but as soon as it gets warm with the ac on it starts acting up. With no ac on the car is fine all the time. I feel like it is a possible tranny issue but i have no idea how the tranny ties into the ac. I got the tranny rebuilt and i think it was a shitty rebuild. Any suggestions?

I have a 95 caprice with a 4.3L V8. When i turn the ac on the car really throttles down and has a significant loss of power/acceleration. I try to only turn it on while cruising on the highway. If the cruise and ac are on while at highway speeds it will be fine for a few seconds then be hesitent for a split second and this just repeats over and over. When the car is cold first thing in the morning i can turn the ac on with no problem but as soon as it gets warm with the ac on it starts acting up. With no ac on the car is fine all the time. I feel like it is a possible tranny issue but i have no idea how the tranny ties into the ac. I got the tranny rebuilt and i think it was a shitty rebuild. Any suggestions?


it is possible the a/c is causing the engine to run hot...this will reduce power....the a/c compressor will use a few HP but should not be that bad...I would check the engine temp a/c on then a/c off...it should not change....

do you have fan clutch,,,,if so it is possible that its the problem..

im not sure if i have a fan clutch. i know the fans are electric and one of them comes on when the AC is turned on. How could i find this out?

im not sure if i have a fan clutch. i know the fans are electric and one of them comes on when the AC is turned on. How could i find this out?


fan clutch would be non electric...
since you have 2 fans and one comes on when a/c is on this part is normal operation....

did you measure engine temp when a/c on,,,,,a/c off ,,,?

engine temp stays the same on the dash with ac on or off...only time it gets warm is when at an idle in traffic or a light...only gets half way at most, then when the car starts to move and air flows through the front grill temp goes back down to regular.

engine temp stays the same on the dash with ac on or off...only time it gets warm is when at an idle in traffic or a light...only gets half way at most, then when the car starts to move and air flows through the front grill temp goes back down to regular.

with the a/c on in traffic vehicle stopped ,,the temp gauge should not go to 1/2,, ....but stay at the 1/3 level....

the fan should keep the engine at the operating temp of 190 deg f approx...with the 180 deg thermostat..with the a/c on...

this is probably air in the system...did you bleed the coolant system???


if the engine is detonating the timing will be retarded and you will loose power when the temp is over the normal 1/3 area..

how does the coolant look...what type coolant...when did you replace the coolant,,,did you flush out engine ever?????

The temp guage only goes to half when vehicle is stopped at idle or traffic with the ac off. when stopped in traffic with ac on it is well below 1/2. coolant flush was done less that 10,000 miles ago. not sure the type of coolant that was used. It is green. car really does not get hot at all.

the throttle response is just not good with the ac on and car is hesitant as well

The temp guage only goes to half when vehicle is stopped at idle or traffic with the ac off. when stopped in traffic with ac on it is well below 1/2. coolant flush was done less that 10,000 miles ago. not sure the type of coolant that was used. It is green. car really does not get hot at all.

that is normal...I would next check the exhaust for restrictions/back pressure....this would cause a loss of power under a higher load..

one way to check this is remove the O2 upstream sensors and see if the power loss is gone...

I have the 4.3 V-8 engine in my 96, 76K miles, it does the same thing with the AC on, surges, can sometimes barely climb hills with the AC on without constantly shifting back and forth, and sometimes has trouble keeping up on the highway. Seems to put a large drain on engine power and improves dramatically when the AC is turned off. One thing I did notice is that is seems to change when getting gas, sometimes it improves with the middle octane gas, but it's always the same until the next time I get gas. Already changed the fuel filter (had black swirls in the gas when it was removed).
Maybe it's just because it's a low-HP engine? I did notice an exhaust drone coming out the back exhaust pipe with no external leaks, I'm thinking that maybe a broken baffle in the muffler may be causing a restriction? Otherwise runs very nicely. Thx.

The throttle position at which the AC compressor is turned off is adjustable in the pcm programming. You might find a nice improvement in drivability by having that adjusted and some other stuff too like shift and lockup points.

You could say have the AC compressor turned off at 30% throttle instead of 90%, you wont stay at 30% long enough for the car to warm up inside but you would have that extra power during brisk acceleration.

The 4.3l L99 is not a bad motor but it is taxxed a bit by the demands this car places on it especially with the gearing these cars have. These cars respond wonderfully to a little modification if you are willing to do so.

what little modifications would you start with?

I jumped right into bigger things but I think if you found a 3.42 axle from say a 93 would be a nice improvement and since it is a factory ratio is comfortable to anyone even if they drive a LOT on the highway. Actually most guys looking for performance jump to 3.73s.

I suggested finding an axle because a civilian L99 car is likely to have the 7.5" axle, the LT1 cars and earlier 9C1s and probably some other option packages got the 8.5". I would not throw money at the 7.5".

Some other little things like replacing the rectangular baffle after the MAF with a piece of PVC is a nice gain, rerouting the coolant so it does not go through the TB anymore is nice, just run it from the pipe that comes up the passenger side of the intake and connect the hose from the driver's side of the TB to it so the coolant goes through that pipe straight back into the surge tank.

Do some reading.
http://www.impalaclub.com/naisso/ss_handbook.pdf

that is normal...I would next check the exhaust for restrictions/back pressure....this would cause a loss of power under a higher load..

one way to check this is remove the O2 upstream sensors and see if the power loss is gone...

Just don't forget to tell him to drive with his windows down as this will cause exhaust gas to enter the passenger compartment, and could cause a fire from the hot exhaust gas if it's directed against anything flammable.

Seriously, this is redneck engineering at its worst!

The other day I flat out called jcat an imbecile on here. I know he means well but I think it has been decades since he learned anything. Much of what he posts is old wive's tales, flat out wrong, or sounds like he opened a Hayne's manual moments earlier.

People like him are what drive the knowledgable folks off of these forums. Not eveyone is as stuborn as I am and willing to put forth the effort to constantly correct them.