I apologize if this has been covered before, but I've searched the forums and I can't come up with something that has exactly these symptoms. Plus what I have read only confuses me on what it might be.

Here are the symptoms:

A/C works fine until I've been on the highway at least 45 minutes to an hour. The symptoms will not appear of the truck is just idling. The dealer let it idle for 2 hours and the symptom did not appear. I've also driven at slower speeds for extended periods without the problem appearing.

What happens is that the cold air coming out the vent will slowly reduce until it is just a "trickle." The air is cold and the fan makes the same amount of noise, but the air flow through the vents is severely reduced.

I can resolve this problem by turning off the A/C compressor (turning off the "snowflake" button, but not touching the fan or vent control *****). After about 30 seconds to a minute, the air flow increases to its normal amount. I'll then turn the compressor back on (again, touching only the "snowflake" button). The A/C and air flow will work normally for about 20 or 30 minutes, then the air flow will restrict again and I'll turn the compressor off and it will increase.

I've read some of the "blend door" discussions and I can't tell if that's the problem here. Any help would be appreciated.

 

Sounds like to me the AC evaporator is freezing up. Is the AC set to recirc when this happens? If so turn off the recirc and allow warmer outside air to flow through the evaporator core.

Also the freon can be on the low side which can also cause the freezing issue.

MikeyB

 

mine had the same problem ended up being the blower motor

 

The A/C is not set to recirc when this happens.

I had the dealer check the freon (more than once) and they said it was fine. That was their first response, as well. Maybe I should get another opinion?

Thanks for your quick reply...

 

What was the actual problem with the blower motor? How difficult/costly was it to fix it?

Thanks for your reply!

 

the blower would make ticking noise and would stop working all i had to do was kick it and it would start working again dealer took care of it under warranty

 

Here's a thread from a few years ago about the same issue. Freon might be on the low side of the pressure operation range and just bringing to the high side of the range can solve the issue. Or it could be a bad evaporator fin sensor.
https://www.dieseltruckresource.com/...ght=ice+sensor

MikeyB

 

There is also a TSB for relocating the fin temp sensor. Do a search on here for it.

 

Doesn't sound like the same problem, but thanks for the effort.

 

Thanks. Did a search and it appears there is some confusion as to whether there is a TSB or just some kind of memo somewhere. Any insight?

 

Don't think there was a TSB on this. Only a memo.
https://www.dieseltruckresource.com/...tor+fin+sensor

MikeyB

 

My 03 did exactly that- freeze up the condenser.

The dealer moved the temp probe, but if it was 100+ and humid it would still do it sometimes.

Setting it on recirculate helps. I think once the moisture from the air in the cab has condensed (and probably frozen) it then doesn't build up additional ice.

Also make sure the drain tube on the firewall is clear and not clogged by a clump of mould or anything.

The fan motor is held in with 3 screws, and you can just drop it down and unlock and unhook it's connector. Next time it happens, you could do that and look to see if the condensor is frozen and/or plug the fan back in and turn it on to verify it is working (since the noise is the same I bet it is).