Howdy all,

We just got back from a 4 week road trip hauling a fifth wheel halfway across the US. We have a 99 f250 7.3, and ran the AC most of the time, but it wasn't ice cold. On the last day, we lost AC part of the time and alas, there is red dust all over the place near the clutch, so it needs to be replaced (or maybe I could get away with just re-gapping it?). In any event, one of the reasons we had to run the AC the whole time was that even when it was cool-ish outside, the air blowing in through the vents is somewhat warm. With the 6 of us in the truck cab, we needed some air moving, so it had to be AC.

I took the heater core cover off (I think that is what it is, behind the glove compartment) and have verified that the blend door seems to work. As far as I can tell, when the dial is turned all the way to cool, the door opens all the way.

So does anyone have any ideas what could be going on? I can't tell where the air for the vent comes in ... maybe it is blocked or goes past something too hot?

Any help would be appreciated.

 

Can you check coolant temps? That much towing might be taxing your truck and causing elevated coolant temps. I would try that. An advanced scanner, torque pro (or like app) on a mobile device, or Auto Enguinity can check. Down and dirty methods include cheap IR thermometers at the coolant bottle or upper water pump flange. I would check this to be safe.

Reason being is, the heater core always has hot coolant flowing through it and the air is passing over it. Even in AC and MAX AC unless you have a shut off valve installed. That will cut off the flow in MAX AC. Only some 04+ trucks came factory with the shut off valve.

For your viewing pleasures.

Superduty - Max A/C Mod (Colder Air Conditioning):

 

my 99 a/c just started the same thing cool but not cold a couple weeks ago , turns out the clutch was failing worn out I did the max a/c mod described above with the ranger water valve and springer pops mod on the clutch . worked sweet my vents are blowing 42 degrees now in 95 temps!! on max a/c after 1/2 hour rolling down the highway

 

I do have torque pro, but didn't think I could read coolant temp (it's an automatic). The dummy gauge on the dash never moved much but I'll have to try some other way (I have the kiwi plx, so can add probes, I think). The clutch is on the list of things to do and I'll look into the shutoff. It doesn't get very hot here, so I'm not sure it's worth the cash, unless we go for another road trip (it was fun, 9, 6, 4, and 1 year old in the back seat!).

 

You're right, the coolant temperature isn't available via the OBD data on a truck with an automatic. You could conceivably stop after a long pull and use an infrared thermometer, but the problem is probably just that air is getting past the seal on the blend door. IIRC it's just foam, and they were never known to provide a very good seal even when new.

 

I added a manual valve, and really noticed no difference, either with the AC on or off. I measured center vent temps with an accurate thermometer. YMMV - it seems like it has worked for many people on this forum.

 

When I put the ball valve in my heater hose, it did drop the vent temps by quite a bit. I think it was somewhere around 8 degrees.