LilSlo1

iTrader: (3)

This past Saturday I was on my way home from Michigan. I was on the highway runnin about 80mph, had the A/c set to bi-level and it was on the 2nd to lowest blower speed.

All of a sudden it started to feel like it was getting warmer in the car so I turned the blower speed up to high. I could hear the blower running but it was barely blowing anything out of the vents. I then switched it from bi-level to max. Now I could really hear the blower motor running but the air wasn't blowing for **** out of the vents almost as if something was blocking the air inlet at the cowl.

I tryed all different settings, max a/c, normal, vents, lower vents and defroster, but it seemed like the little doors or deflector in the heater box were not moving. Also I put it in neutral and revved it a few times hoping that mabey I'd get a little more vacuum built up. At this point I was a little concerned that mabey a vacuum line broke, fell off, or got burned by a header, or at worst the engine had no vacuum, but the engine was running fine; or mabey one of the diaphrams busted. When I would turn the vent selector (don't know what else to call it) I could hear the normal vacuum noise at each selection, but as I said before it seemed like none of the little doors or whatever were moving in the heater box.

Anyways when I got home I checked the cowl and there was no blockage for the creature comfort air inlet, so then I decided to pop the hood for ***** and giggles and the A/c lines and the resevoir has frost on them. And for how must frost were on those I am sure the evaporator was the same and was preventing air flow thru it to the cockpit. Usually I know these tend to get condensation them, but frost? I just got home from an hour and a half trip, so the engine compartment was warm and it was also about 85 degrees out.

Has anyone else ever had this problem ? I can understand that the A/c system got frost all over it or even frozen due the fact that there wasn't enough air blowing past the evaporator, but what caused the lack of air ? Or if it did just decide to freeze up, why ?

I doubt its possible, but mabey the cockpit pressurized and the blower motor couldn't over power it ? (I highly doubt that our cars seal up that good.)

Sunday I decided to enjoy my t-tops. Just for the hell of it I tryed my A/c and it worked fine. All of the vent selections worked properly and I had proper air flow out of my vents.

WTF ??

LilSlo1

iTrader: (3)

anyone ??

Travis99LS1

iTrader: (2)

I have experienced the exact same thing with my car. Our cars have a variable displacement a/c compressor..if the compressor doesent reduce the output according to either evaporator temperature, or system pressure..the evaporator will definately get cold enough to cause any condensation to freeze up. To be honest, i havent really tried to diagnose it any further..I live in florida right now so its hot as hell..It usually doesent do it unless i've been driving on the highway for about an hour or so...which i hardly ever do so i'm not to worried about it right now. I will try to find some more information about it though, and let you know. All you have to do is turn the AC off and usually my'n after about 10-15 minutes will melt any frost, and than it will work fine for another hour or so.

LilSlo1

iTrader: (3)

I'm glad I'm not the only one with this problem. Next time it happens I'll definatley try to thaw it out, and see if it works again.

gr8one99SS

iTrader: (4)

it will work once it thaws my has been doing the same thing.

speedy_2

iTrader: (12)

My dads car would do this as well. 87 Oldmobile. As well as my Moms 94 Jeep. We did the same thing, turn it off and let it thaw. But, I've never had that problem with my own cars. I've had a 94 Camaro, 98 Cadillac, and now a 98 Camaro.

siniSSter

iTrader: (2)

All vechicles will do this if they are exposed to an extreme airflow of the condensor. Your suction side of the A/C system should be cold, even frost on it. Your high side shouldn't though, if your experience this often you could be overcharged. When you've been driving down the road for a while, Do you hear the compressor clutch engaging on and off? The best thing to do is get a manifold guage and check your suction and discharge temperature accordingly.

bighank

I believe this can also occur from a LOW charge of freon. Get some guages
$39 at Harbor Freight and see what your pressures are. Specs are in the Helm Service Manuals. You might be undercharged. BIGHANK

JR HAWK 9

iTrader: (3)

Like stated above, we have the variable stroke V7 compressor, it doesn't cycle like you mention, rather it just destrokes when needed.

OP, mine also sometimes freezes up after driving on the highway for awhile.

Rhode Island Red

iTrader: (2)

I had the same exact thing happen to me coming back from NH and Camaro and Firebird Day 6/9/07. I was crusing in 6th, Mid 80's, it's been over an hour and a half of constant driving. I noticed that the airflow from maxed was reduced to low low-med despite it on max and the air was getting warmer and warmer. When I pulled over for food and gas, popped the hood and viola ! The evaporator had a nice thick coating of Ice. This was my first long trip since getting the cam/headers done last November.

After talking around, the best educated guess was as stated above, a low charge of Freon. I still need to check with a gauge/gage (check your display on your F-bod) . Hope that is it

question: what refrigerant and how much does 4th Gens need (98+) ?

If that is not it, guess I'll have to have a shop take a look at it.

Mr Incredible

I have that problem, too. Just this last week on a couple of trips between Omaha and KCMO. The cooling stops because the fan slows, not because of cooling flow.

Turning the control to non-A/C settings gets the fan moving again immediately. Going back to A/C, the fan continues to blow until is slows & almost stops again. The time to this problem varies.

Annoying, but not gonna kill me. Curious to know what's up. Could it be frost in the evaporator stopping airflow?

Travis99LS1

iTrader: (2)

It doesent sound likely at all man. Reason being is air always passes thru the evaporator..as long as you have the blower on, air will pass thru the evaporator. So when your evaporator freezes, it doesent matter if you turn the a/c off or not...no air will pass thru the evaporator until it thaws out.

Starion

iTrader: (5)

Your best bet is to get some manifold gauges like bighank suggested. For $39 you can't go wrong......it would cost that much to have any mechanic hook his up to your system. At that point you'll get an idea of whether you're over or undercharged. The solution to your problem may be as simple as altering the freon level.

LilSlo1

iTrader: (3)

thanks for all the suggestions guys !

JR HAWK 9

iTrader: (3)

also, visit THIS FORUM, seems to be lots of knowledgeable guys.

From what I read, our V7 compressors are one of those that is hard to use pressures to see if we are over or under charged. I was told the best bet would be to evac the system and then refill with the correct amount of 134a....which is 24oz I believe.