Periodic Surge with A/C or Defrost

[Chris611]

I have a '97 6,.5L and notice a surge every few minutes when I operate the truck with the A/C or Defrost on. Its pretty noticable. Is this the compressor kicking on and off? Is this normal and any thoughts on what to check.

thanks
Chris

[catmandoo]

yep sounds like compressor.

[Chris611]

Thanks for the reply. Does that mean that the compressor is going bad or is that normal operation. I hate the thought of the A/C compressor having that big of an effect on the engine.

Chris

[catmandoo]

thats the way they work,helps defog the windows faster.

[ZZ]

The A/C compressor cycles more in the winter than in the summer. And yes, you will feel the load on the engine changing.

[BuffaloGuy]

Here's a trip to save some fuel in the winter.

Unplug the AC compressor. Then, when you have the heat on the windsheild you wont have the A/C running too.

The only reason you need the A/C in the winter is to dry the air so it will defog the windows. If you don't need dry air then you don't need the a/c in the winter.

It will increase your highway mileage about 2-3 miles per gallon.
Ken

[BrentN]

Word of caution regarding unplugging the compressor during the winter:

The secondary reason the ac is cycled on and off during the defrost cycle is too also provide lubrication for the compressor in the fall and winter months. The refrigerant also has lubrication properties.

When mine gets too annoying, I just reach over and go back to vent mode and when and if we start fogging up, I turn it back onto defrost briefly.

Thats my $.02

[rjschoolcraft]

Ditto on the lubrication issue. The seals in A/C compressors used to dry out during the winter months, then leak when summer came. The engineers fixed that by cycling the A/C when the defrost is on...with the added benefit of drying the air.

To confirm that this is the source of your surge, stand in front of the vehicle with the hood up and engine idleing in defrost mode. Watch the A/C compressor. You can see the clutch engage and disengage...if this coincides with your surge, you've found the source.

[Kennedy]

Having AC cycle with defrost is often a good idea. The idea is to lower humidity in the cabin so that frost does not occur on the inside of the glass. The newer computer climate control modulates the activation of the compressor based on humidity. Standard HVAC vehicles just run the AC when defrost is on.