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Engine surges when heat or A/C is on

Tiny
MGOBLUE78
  • MEMBER
  • 2000 MERCURY MARQUIS
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 138,000 MILES
When in gear at a stop with heat or A/C on the car will lunge/engine surge. Does not do this when heat or A/C is off. Any idea why it does this?
Saturday, April 27th, 2019 AT 10:19 AM

3 Replies

Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
There are literally dozens of possible scenarios that can cause this. First start with the basic visual inspection of the intake and hoses for vacuum leaks. Also remove the belt and turn the compressor by hand, it should turn relatively easy when rotating the center part of the pulley, if it is as hard as opening a Gatorade bottle, then the compressor is bad. Also verify that the voltage does not drop excessively when the compressor kicks on, lower than 10 volts will indicate a voltage issue which could be anything from a weak battery to a weak ground.
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Saturday, April 27th, 2019 AT 10:48 AM
Tiny
MGOBLUE78
  • MEMBER
  • 12 POSTS
Thank you for the help. I will check this out.
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Saturday, April 27th, 2019 AT 11:02 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Hello,

It sounds like the AC is low on charge which cycles the compressor, but to be sure here is a guide to help you test the system charge:

https://youtu.be/uZrQCGwXfek

Please let us know what you find. We are interested to see what it is.

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Monday, April 29th, 2019 AT 1:07 PM

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