Just made a 14 hour drive in my '06 F150 KR. Going up, I split the drive over two days. About four hours into the drive on the first day, the A/C started acting up. It seemed to want to blow cold, but the fan was not pushing the air very hard. The blower/evap box under the glove box got louder too. That noise is what really alerted me that something wasn't right. We made it to our stop for the night and I wasn't able to look into it.

The next day, about three hours into our drive, it started doing the same thing. It seems like the blower is freezing up and not able to push the air. Turning the fan up/down did not really increase/decrease the air flow... only the noise coming from the blower/evap box. When we stopped for lunch, I took a look under the truck to make sure the condensation was draining through the evap tube. Not only was it draining through the tube, water seemed to be dropping from everywhere around the tube also.

Note: About a week or two before this trip I noticed the air did not seem to be blowing cold enough, so I used a recharge kit. Even after adding a can of R134a, it still seemed to be registering low, but I did not add any more. It wasn't even within the specs listed on the can for the ambient air temp.

After making the two day drive and thinking I was low on freon (might be the problem), I bought another recharge kit. Using the gauge that came with the kit, it said I was at the low side of the pressure range for the ambient temp. So, I did not add any more.

We made the entire 14 hour drive in one shot coming back. This time, it didn't start acting up until nine or ten hours into the drive. We pulled over into a rest stop and while the kids were doing their thing, I turned the A/C off and turned the temp up to 84 degrees. I let it run until the dripping underneath the truck was basically just a trickle... almost stopped. That seemed to unfreeze whatever was blocking the air flow and I was able to make the rest of the drive in relative comfort.

Does anyone know what might be going on? Do you think I should add more freon to get to at least the middle of the pressure range for the ambient temp? Is there anything else I can check myself before I have to have it looked at by shop?

 

The blower fan has no connection to the amount of freon in the system so stop throwing more freon into the system as you may be doing more harm than good. It sounds like the bearings on the blower motor are shot, replace the motor and squirrel cage at the same time. You might want to have somebody put on a set of guages and check to see you haven't overcharged the system.

 

i generally charge mine to around 35 lbs on the gauge when i do it. when you shut off ac and put on heat to drain it did it blow normal after that, if it did then your evaperator was probally frozen restricting air flow

 

Yes. After I put on the heat, it blew normally. The fan speeds increased/decreased normally... or maybe I should say the amount of air through the vents increased/decreased normally... and the 'noise' from the box under the glove box was back to normal.

I'll find someone to check it with some real gauges too.

Is the evaporator freezing because it is not draining fast enough?

 

If the evaporator is freezing you should also see the line leading into it frozen as well.

 

my guess would be that it's still undercharged. what was the reading when you used charge kit?

 

What I remember is that the kit said I needed to be in the 40 - 50psi range for 82deg ambient temp... and I was right about 40psi.

I'm thinking I probably need to stop monkeying with it myself and get it checked to make sure I didn't screw something up with the recharge kit.

 

thats probally best good luck with it

 

I have another vehicle with a chronic problem related to the high pressure switch in the AC system. The switch is supposed to shut off the compressor if the pressure gets too high. If it doesn't activate, then the exchanger gets too cold for too long. If the humidity is high enough, the exchanger ices up and restricts air flow, cutting off the air flow. Turning on the heater melts the ice on the exchanger, and occasionally blows snowflakes out of the vents, to the amusement of my children....

It's tough to diagnose, though. Taking the switch out of the circuit essentially causes the problem you're trying to cure. On older vehicles, the switch is adjustable, but I doubt that's the case on our trucks. You can also replace the switch, but a diagnostic visit is probably going to be the same cost, or even cheaper.

Good luck!

 

I would evac your system, change the orifice tube. Get a good set of manifold guages. Vacuum it down overnight and then add the appropriate amount of 134a. If you do not feel comfortable doing it yourself then take it to a ac shop.