Very strange AC problem

[FloridaState]

Hey guys, sorry for my severe lack of posting...been so ridiculously busy with school that I've neglected my poor X and this forum. But, graduating next month will make it all worth it!

Anyway, on to the problem. In short, my A/C only blows cold at low speeds. I noticed this last weekend when I took a trip to Georgia...the AC worked fine on the way to the interstate, but after a few minutes on the highway I noticed I had to have the AC on full blast and I was still sweating...the air coming out was cool, not cold. I chalked it up to it just being really hot outside and the air couldn't keep up.

Well, I got into Jacksonville and got stuck in a bit of traffic and it started working again, blowing ice cold. Then, after the traffic thinned out and I sped up (80-85mph is my cruising speed) and it stopped again. I didn't put two and two together until I got on the exit ramp in Georgia and as soon as I stopped at the light it started working again, and it worked the entire time I was in Georgia.

I was going to test it again on the way home, but due to the tropical storm, the interstate was closed for a large portion of my travel, so I had to go a back way through some towns and didn't get up to interstate speed. Of course, it worked fine the whole way home where I rarely got above 65.

I run the AC on the MAX setting, and I tried it on the regular AC setting when it wasn't working and it didn't make a difference. It just seems so weird that it won't work at highway speed but works fine around town. I have a trip to Daytona next weekend for the race and I'd like to at least know what the problem is, if possible.

And please, no wise cracks about "just drive slower."

Thanks for reading and any help would be greatly appreciated!

 

[deweyville65]

Hey guys, sorry for my severe lack of posting...been so ridiculously busy with school that I've neglected my poor X and this forum. But, graduating next month will make it all worth it!

Anyway, on to the problem. In short, my A/C only blows cold at low speeds. I noticed this last weekend when I took a trip to Georgia...the AC worked fine on the way to the interstate, but after a few minutes on the highway I noticed I had to have the AC on full blast and I was still sweating...the air coming out was cool, not cold. I chalked it up to it just being really hot outside and the air couldn't keep up.

Well, I got into Jacksonville and got stuck in a bit of traffic and it started working again, blowing ice cold. Then, after the traffic thinned out and I sped up (80-85mph is my cruising speed) and it stopped again. I didn't put two and two together until I got on the exit ramp in Georgia and as soon as I stopped at the light it started working again, and it worked the entire time I was in Georgia.

I was going to test it again on the way home, but due to the tropical storm, the interstate was closed for a large portion of my travel, so I had to go a back way through some towns and didn't get up to interstate speed. Of course, it worked fine the whole way home where I rarely got above 65.

I run the AC on the MAX setting, and I tried it on the regular AC setting when it wasn't working and it didn't make a difference. It just seems so weird that it won't work at highway speed but works fine around town. I have a trip to Daytona next weekend for the race and I'd like to at least know what the problem is, if possible.

And please, no wise cracks about "just drive slower."

Thanks for reading and any help would be greatly appreciated!

Possible the evaporator is freezing over with ice. Mext time this happens, shut the air off for a bit. Go to vent to defrost the evaporator. See how that works. Not saying that is the problem, but I had the same problem on a Kenworth a few years ago during the monsoon season. Real PIA when the temp is over 100 and the humidity is up around 75%

 

[my98nnj]

He's still blowing air, just not cool so the freeze up definitely isn't happening.
Make sure the condenser is clean, check the fan clutch.
Have the system pressures checked and make sure they are ok at higher engine rpm's.

 

[deweyville65]

You tell me if the evaporator is iced up, there will be NO air blowing from the vents? But then you turn around and say if the condenser is dirty, it will cool at low speed, but not at high speeds. Doesn't make sense to me. But then I've been in Az for too many years, my brain must be ffiex.

 

[budwich]

wire in some test leads that allow you to monitor the voltage going to your clutch so that you can see the voltage there at all times from a meter in the cabin. Go for a spin and see what happens... then go from there... this will hopefully tell if you have an electrical issue or a thermal issue (engine cooling air flows, etc). My guess would be improper AC charge levels.

 

[windsors03cobra]

When the evap ices over it air cannot pass thru it so the airflow will be greatly diminished.
Possible overcharged condition.

 

[FloridaState]

Thank you for all the responses...I will try.

budwich, how on Earth would I set that up? lol I wouldn't have the first clue how to get started.

 

[budwich]

some automotive wiring (like those used for trailer connections and such, single lead, multistranded wire).... there are "alligator clips" that allow you to "join" wires by pushing them thru the clip which makes a small cut thru the insulation and connects to the copper conductors (sorry I can't remember the official name). Basically, punch on a clip (with the long test wire attached) on the power wire going to the clutch. run the lead (single wire) back thru the firewall (hopefully you can find a hole some where to feed them thru). Get your volt meter out and connect it to the "test lead" (and to a known ground) and now you will be able to see what is happening under your hood. Go for your spin around the freeway. Obviously, before you go there, you indicated that things work fine so you should be seeing 12v then. Keep an eye on that and the road.... careful now... maybe get someone to drive as fast as you do while you watch...

When you are finished, gets some silicon and coat the wire that was cut by the clip when you remove it to prevent problems there after.

PS. you don't even need to go thru the firewall... just go around the edge of the hood and thru the window / door... its only a single wire.

 

[waskly]

my guess is, you have a low charge, or a restriction, which causes the high side to go high and low side to go low enough that it shuts the compressor off.

start the car, set the ebrake, chuck the wheels, and raise the revs, see if the compressor is still on.