Stephenms

Hey there everyone! It's been getting hotter and hotter lately here in Florida and I'm a little concerned about my A/C system. I have an 87'

The system seems to be sporadic. I have the digital unit, buttons not *****, when it does turn on it's very cold but doesn't blow out very much. On "Auto" setting, air blows from the front 5 vents ice cold but very low even on blower speed 10. The far right vent has no air coming out. The feet vent has slight air flow and the defrost vent has slight flow. No matter what I do I can't get flow to only come out of the front vents. Bi-lev doesnt change and neither does economy. When the blower doesn't work I have to drive over a slight bump, sometimes a big bump, to get the motor to work. Could my issue be a bad blower motor? Not spinning enough to have a high air flow?

Also, my digital unit sometimes won't turn on. It will just be blank and dark. When I'm driving it will randomly turn back on and show the exterior temp and all that. When I have headlights on the unit will not light up the buttons like the stereo does.

Any help is much appreciated! It's hot hot hot here and only getting hotter. Not sure if it's blower motor or just the digital unit itself.

EDIT: I just saw that the unit was not lighting up(no display) and decided to turn it on to seewhat would happen. The system did turn on! Fan kicked on, idle leveled out, no air flow out of the vents but I had a cold lines and a sweating accumulator.

Hooked on Vettes

Appears you have multiple problems. Did you reseat the connector on the back of the HVAC control head?

There is a Gray wire from the dimmer switch that goes to the HVAC control head. That's the wire that powers the backlighting when the headlight switch is in head or park.

When you say the HVAC control blanks out are you talking about just the display and all of the buttons don't work or does only the display go blank and the buttons still work? The display going blank is a common problem due to poor solder joints.

As for the blower speed.
Turn the ignition On. Manually increase the blower speed from 1 to 10.
Can you hear the blower motor speed up. At speed 10 you should have 12 volts going to the blower motor. You can unplug the connector at the blower motor under the hood. The connector plug has two wires. The Black wire is ground and the Black/Red wire is the voltage to the Blower Motor from the Blower Control Module. Should be around 12 volts when the fan high speed is selected.

Look on top of the evaporator housing at the two electrical connectors.
Verify none of the wires are burnt at the connector.

Cliff Harris

If the air flow doesn't change with changes in the HVAC control head function buttons you might have a problem with the vacuum that makes all this happen. It's fairly common for the vacuum check valve next to the distributor to fail. It's a $4 part at any auto parts store.

I had a problem where the blower would sometimes not work. It turned out to be corroded pins in the connectors on the blower control module.

The lighting for the HVAC control head comes from the radio. Some aftermarket radios will not supply that voltage.

The control head is powered by the GAUGES fuse. It also gets power from the CTSY/CLK fuse (always on) to maintain the settings when the ignition is turned off.

Stephenms

I appreciate the responses!

I am referring to the units display going dark/black and the controls still functioning. As for the blower test it checks out 12v at speed 10. The vacuum check babel was recently replaced and is working. Hopefully I can do some more tests today and I'll update

GKK

It might be the Blower Control unit, (black box) located above the gas pedal that has a couple of cold solder joints.

My previous 89 Vette, had weak air blowing out of the defrost vents or the floor vents. I removed the blower control unit and found the tips of two solder joints (both, located on the same side of the box) that seemed loose. I reheated the solder and it flowed back onto the copper tips.

I turned the AC on and switched from Bi-level to Normal and everything worked again!...

Also, the Blower fan in my 89 Never felt strong even after replacing with a new one. The blower fan in my 91 Vette is a lot stronger...






.

Hooked on Vettes

With 12 volts at the blower motor it should be running at full speed.
You could remove it and spin the squirrel cage by hand and verify the motor spins free. I believe they used bushings on the motor shaft and not bearings so they do go bad.

Don't be surprised if you find a rodent has built a nest in the evaporator housing.

As for no air coming out of the AC duct on the Passenger side, crawl under the dash and see if the hose has detached.

For the back lighting, there are 3 bulbs on sockets (194) that provide lighting for the buttons when the headlight switch is in Park or Head.
There is also a Display Dimming signal that came from the Radio that would dim the Digital Read out Display. If you install an aftermarket radio this function is lost and the HVAC Display brightness stays at a fixed brightness.

Not much I can tell you about the intermittent HVAC display. Only thing you can try is to resolder the circuit board and hope for the best.
It's a very common problem. I tap on mine with my finger and it works for a couple of days.

Here's a picture of one of the 3 bulbs used for the backlighting.

Stephenms

I did see the Blower Control unit (black box above gas pedal) you were referring to. I do not have enough time to fiddle around with it today though. I did notice the connector to it was a tad loose so I lightly pushed a little more and felt a "click." At this point I don't know if this fixed the vent issues because when I turn the A/C on the air won't go through the vents or the blower motor won't turn on or something. I got a second opinion from C&S Corvette from a shop they have down here and the mechanic I talked to said it could be that the vent doors are either broken or stuck way open and not allowing enough air pressure to feel like a lot of air going through. He pointed out a slight tick when I first turned the key to "on" It was a click or even grinding sound behind the passenger side of the dashboard, directly behind the "cushion" Almost like an actuator was getting stuck trying to open or close. This occurs even when the A/C unit is turned off. After 5 seconds or so it stops ticking and goes quiet. Sometimes while I'm driving it will do it again and stop. I've never noticed this till he pointed it out!

Also, I just tested the controls one more time from the unit and from speed 6 to 10 no air comes out. But from 1 to 5 the air would come out. Still very low air flow but if I out my hand directly up to the vents closest to me I can feel ice cold air very lightly. The passenger vents have much less air going to them.

GKK

Not sure about the 89 but, my 91 Vette has a vacuum actuator underneath the passenger side dash near the floor, that switches airflow from the floor to the upper vents.

Maybe, that vacuum actuator is sticking?...







.

Stephenms

That's exactly what I'm thinking. Tomorrow morning I'll take the bottom dash apart to see what I can find. I'm hoping I don't have to take this entire dash apart to get to the vent doors I need.

Stephenms

The air pressure issue was a bad blower motor. I replaced it today and it's blowing ice cold air. The only thing is is that it's blowing air still out of all the vents and with the A/C on and at 1400 RPM I will hear a rattle unless I turn off the A/C. I'm not entirely sure what that could be. It goes away once the engine either drops RPM or Increases higher RPM. As for the vents I believe it's a vacuum line issue. I heard that the vent doors rarely go bad but the air vent actuator system does.

GKK

The rattle could be the Serpentine Belt Tensioner Pulley. The pulley bearing might be worn causing the rattle when under load with the AC on.

Stephenms

I will confirm that it is the pulley or just tensioner itself just so I'm not throwing money at it. I appreciate all your help!

Stephenms

I could not verify it being the compressor clutch or the pulley. It certainly sounds like metal bouncing around. The tentioner pulley is all over the place. My power steering pulley and AIR pulley are wobbling. PS pulley is TERRIBLE! Could be a slipping belt and the excessive load of the A/C turning on.