Thread: A/C Blower fine but airflow weakens after long distance?

Hi all,

I've been perusing the incredibly helpful grandprixforums for a while now, as I'm trying to learn more about my GTP and car work in general. I did my research on this problem but couldn't seem to find anything, so I'll go ahead and post for once! I'd greatly appreciate some advice.

So the A/C blower works fine. This is the digital, automatic control A/C, by the way. Temperature settings work fine. Driver/Pass dual works fine. Everything is great... until I go on a longer high-speed highway journey, say an hour or two. At some point along the way, the air will suddenly reduce to a trickle from the vents (both the driver and passenger vents stop working at the same time). Now, the blower doesn't stop - but I can hear the air getting lost behind the dash, it sounds like. So very little reaches the cabin through the vents. This is true whether hot or cold. Sometimes messing with the vent selector or temperature fixes it temporarily, sometimes not. Turning the car off for the night and coming back in the morning ALWAYS fixes it, unless I drive an hour or so again the next day.

This is also sometimes accompanied by a faint clicking or winding sound from behind the dash. I researched the A/C trouble codes and checked them - I've got 105 and 106, indicating historic faults in the Left and Right Electric Actuators. Sometimes the codes also become 05 and 06, indicating current faults.

I found replacement parts, and I read the write-up for replacing the doors here:
http://www.grandprixforums.net/blend...ent-21941.html

The only other reference to this issue I found, anywhere on the internet (!), was here:
AC/Heat Problems - Blower going, but no air from vents - Car Forums and Automotive Chat

So here's my question:
Don't the electric doors, the ones reported in the trouble code, control the mixing of hot and cold air? Would they really be responsible for the gradual loss of cabin airflow? The HVAC computer thinks so, yet it sounds like a vacuum issue, because it only occurs after prolonged driving at high speed = higher RPM = lower vacuum pressure, and because the driver and passenger are affected equally, and because there is otherwise no trouble with temperature blending. Has anyone experienced this problem or seen it as the result of those electric actuators vs. the vacuum system?

Thank you all for your advice and support of the community. It's one I hope to become part of and contribute to, if I ever learn what the hell I'm doing.

Komrad36

It sounds like is evap core is freezing up. I have seen it a few times before including on my wife's Camaro. When you park it for a little bit do you notice quite a bit of water coming out of the drain in the firewall and hitting the ground under the engine? Usually this is a sign of the ice melting. Most of the time it means the A/C has a leak / low on freon and this is causing the freezing up. It could be a bad compressor or switch causing the compressor the over pressure the system as well.

Interesting! I never thought of that.

Yes! There is an unusual amount of water that drains out after I stop. I went out to Advance Auto, purchased the correct R-134a and a gauge, and checked the pressure: it was about 30% below optimal. I filled it to the middle of the recommended range, so I guess we'll see what happens.

The A/C button audibly engages/disengages the compressor clutch, and it automatically disengages after a while, so the compressor seems ok. I'll keep that in mind as a possibility though.

I'm leaving the country tomorrow for 3 weeks, but after I return I'll make sure to go on a long drive and see if adding refrigerant solved the issue and post back. Thank you so much for your help!

Komrad36

After a couple months of experimentation and consulting with local mechanics, I found the (strange) solution that I thought I might share in case anyone else ever experiences this problem. My A/C system was missing the following AC/Delco part number: 22697948
https://acdelcooutlet.com/index.php/15-33323.html

It's a simple, small, plastic tube, less than $5 even at the stealership. This tube must have fallen off somehow and was thus not present on my car.

Its purpose is to allow water from the evap core to drip onto the ground while the car is in motion - it curves down and back to prevent air from getting in, letting the water fall freely. Without this pipe, air would shove into the opening to the evap core, preventing water from escaping and thus eventually clogging up the core with condensation.

Thanks all, and I hope this might be useful to someone in the future!

Komrad36

Hi all,

Unfortunately, a month later, it seems I spoke too soon. In the meantime I also replaced both electric actuators as their internal gears were cracked. This removed all errors from the CJ2 and made the temp selection nice and quiet. Unfortunately, the original problem remains.

So to recap: after a longer (20+ min) drive, sometimes the A/C airflow from the vents will slow to a trickle. But the blower doesn't change, I can still hear it just as strong as before. The air sounds like it's getting
"lost" behind the passenger side of the dash, or the glove compartment.

Screwing around with the mode selector switch seems to cause this failure sometimes, though it also happens spontaneously even if I don't touch the switch and it's set to head vents the whole time.

With those clues, it seems to be a vacuum issue, or mode selector flap issue. I know very little about these systems and am having trouble finding out more online. Please advise.

Other thoughts:
-refrigerant OK
-this is the automatic A/C control, 1998 CJ2 model

Thanks,
komrad36

when you changed the actuators im sure you saw the round vac pumps close to the dash, they are vac controlled. fire up the car, work the selector and watch the rod to move, theres one on each side. make sure they move and change the air flow direction. ( def, vent, floor, mix of floor and def, mix of vent and floor.

Okay, I'll do that first then and report back. My concern is that they will likely work just fine when I look at them... if that's the case, what could cause them to fail after some driving? Vac leak is the only thing I can think of, or old and friction-heavy selectors.

Thanks Gpmadness and Scottydoggs!

Komrad36

it could be loosing vacuum, its the vac line that comes off the top of the super charger, then to the pass side fire wall, down the fender to under the fuse box area were some cars have a T, one side would go into the cab via that cluster of wires, and the other side leads to a vac ball in the driver side fender, under the head light area. ( some cars dont have this, some do) but they all lead into the cab from under the fuse box area.