A/C blowing hot

[AWD985.0]

Hey all, I’ve looked all over the forum and haven’t found anyone with a similar problem or a solution, so I figured I’d make my first post. I’ve got a 98 EB with the V8 and AWD as well as the automatic climate control. My problem is that when I have the A/C on, every time I moderately apply the brakes or go downhill there is a loud pop from under the dash and it blows hot like the heater is on full blast. Once it’s started blowing hot the only way to get cold air again is to shut off the A/C and turn it back on after accelerating quickly. Also, when it’s cold outside, it will not blow hot until I brake hard enough to cause the pop. Any help or insight would be greatly appreciated.

 

[Pete Deering]

Hey all, I’ve looked all over the forum and haven’t found anyone with a similar problem or a solution, so I figured I’d make my first post. I’ve got a 98 EB with the V8 and AWD as well as the automatic climate control. My problem is that when I have the A/C on, every time I moderately apply the brakes or go downhill there is a loud pop from under the dash and it blows hot like the heater is on full blast. Once it’s started blowing hot the only way to get cold air again is to shut off the A/C and turn it back on after accelerating quickly. Also, when it’s cold outside, it will not blow hot until I brake hard enough to cause the pop. Any help or insight would be greatly appreciated.

Sound like the blend door. 1a auto has a video on replacing it on YouTube.

 

[DR98FL]

The system uses engine vacuum to open and close doors to direct air to defrost, panel vents and floor vents. Varying combinations of vents at one time as selected.

The power brakes uses engine vacuum. You've got something happening with the vacuum.
The hot and cold air blend door is controlled electronically. Blend doors cracking and failing is a big problem in the 95-01 Ex's.

When your a/c is working does it come out of the side vents? If it comes out of the defrost vents only, it usually is the vacuum ball reservoir located under the air filter box pass side under hood.

If you pop the glove box door open. Squeeze on each end of the glove box and it drops down. Your then looking at the duct work of the climate control system. To the left should be a connector with 5 vacuum lines going in to it. Or they might be on the back of your EATC control unit. Look up under the dash and you can see some of these vac control motors.

I would examine the vacuum lines carefully.

black line is the vac feed from under the hood to the system.
white line goes to the inside/ outside air intake door and the heater core hose shut off valve.
Yellow line floor- panel vac motor
blue floor - panel door
red panel vent - defrost door

You may have to pop the EATC control unit out to check those lines as well. Drive with the glove box out and down, to help locate the sound.