Skip the auto shop - Our mechanics make house calls

Q: poor brake performance when car's ac is on

asked by on

When driving with ac system on. Usually in warm / hot weather. Braking performance is significantly poor. Pushing harder on the brake pedal doesn't seem to help. Wondering if this is common? How would I fix the issue?

My car has 230000 miles.
My car has an automatic transmission.

A: Hi there. Most of the time this is due to a...

Hi there. Most of the time this is due to a loss of vacuum in the engine. A loss of vacuum drastically reduces the performance of the power brakes. I typically start by checking for any vacuum leaks in the engine. If there are none, then it may need a new vacuum booster. If you are going to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to inspect your braking issue and make any repairs that are necessary.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Stopping lowers the RPMs

When a vehicle is running all of the accessories and systems used to run the motor all put load on the system. This being said, anything from turning on your headlights to depressing your brake pedal puts extra load on...

Q: Thermostat has gone bad

It is possible that your thermostat could be causing this issue. It is also possible that a bad coolant temperature sensor is sending false information to the computer. I would ask for help from one of the mechanics at YourMechanic...

Q: Master Booster, 2001 Lincoln Continental

Hello - these symptoms do indeed suggest that the brake power booster has failed. A hissing sound as you describe indicates that the rubber diaphragm in the booster has ruptured, reducing brake power assist, and leaking air to the engine...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...