Normally my AC blows really cold on normal, 40 to 50 degrees colder than ambient. Freezes you out on the highway even at ambients of 110. Last weekend I turned it on while on the highway, ambient was around 80. The air never got below 60, was not really comfortable. So today I took it to a reputable AC place. They evacuated and recharged, stating it was low by about one third of a pound. They said compressor pressures measured excellent, and they obtained 40 degree air out of the center vent on recirc (max).





So I go pick it up, drive around on normal, still not real cold. On recirc it will get cold, but I do not normally like to run on recirc. So I took it back to find out what it could be. They told me I should be using recirc, I said bull**** it ran cold on normal before. I asked if maybe the heater valve was not closing, they said my truck doesn't have one. From what I have read my 2002 does have one. They also said they have seen the heater door warp and not close all the way. I asked about clutch gap and they said if that were an issue the air would not work at all, which is contrary to what I have read also.


Any ideas?

 

If your truck has a heater core shutoff, you should see it in the line going to the heater core. If it was a clutch gap issue, the temperature would most likely get very warm for a period of time, then suddenly start cooling again. It is possible the blend door actuator isn't closing the airflow from the heater core off all the way, or it isn't sealing tightly.

Clamp off one of the hoses and see if makes a noticeable difference in the vent discharge temperature. If it does, you're getting heated air from the heater core.

 

Our trucks didnt come with the heater control valve, you cant get the kit from diesel site, but I never needed one my a/c cranks. you really should use recirc when its super hot or humid out, you still get some fresh air in but not that much, it's harder to cool 110 degree than 70 degree air so you should use the recirc on really hot days, first thing after running your air do you have water dripping out the drain? open your hood and look at the low pressure lines are they sweating? there on the passenger side, the hose that runs into the receiver drier. If no to those questions you have a problem with the a/c systems. if the answers are yes, you may need a blend air door motor, they go bad alot, sometimes the tabs on the door break and if you cant flip the door from heat to air, no good. you can listen to run the truck radio off, blower on low than turn your temp control from cold to hot and you should be able to here the door open and close with a slight thud, and you should notice a change in the air flow, when it passes the evap and heater core the blower slows down, not as much air is felt. Let me know than we go from there.

 

What they said sounds legit to me. It is consistent with how my truck operates. I did add a heater core cut off on mine that activates when I run it on max.

Ryan

 

I did a simple cut-off on mine. I just put a ball valve in one of the heater core lines. Of course I need to raise the hood to switch it.

 

i always run max air. or as some call it, recirculate air.
think about it for a second.it is a lot easier to dehumidify the cool dry air in the cab, than it is to dry the hot humid air outside the truck.

and i do all my own AC repairs.
took the courses many many years ago, and am EPA certified to do AC repair and buy refrigerant.

 

Exactly! I do this, too. By design the AC does not get as cold with outside air blowing across the evaporator.

 

I used to be in the "Max Air" camp as well until I had several vehicles develop bad odors/mold in the evaporator housing. My Grand Cherokee was the worst, smelled like dirty socks. Evap Fresh and similar treatments did not work. I had to drill a 1/2" hole in the housing and flush it out with the garden hose, and keep it on fresh air all the time.


On my truck, as soon as I switch to Max there is a slight musty smell. Granted, I do have a super sensitive nose.


On my 1987 Mercedes 300D there is a dash switch you push for recirc which gives you 20 minutes of recirc, then it automatically switches back to outside air. There must be a reason they did that.


Today I am going to try the suggestions to see if it is heat from the heater core warming things up.

 

Another thing to consider is humidity. If it's been abnormally humid there, the vent temperature will be higher than you're used to.

 

I think you nailed it. Today I pinched off the supply to the heater core and drove around most of the day like that with 40 degree air blasting me. Then, later in the day when it was 90 degrees out I drove about six miles on the interstate with the hose still pinched off, stayed very cold, 40 degrees. Thought I had it figured out.
Then I removed the pinchers and drove the same 6 miles back. 40 degrees. The only thing different is the humidity was down some, we have had horrible humidity here lately.


So I probably spoke too soon, but I am keeping those pinchers on the seat just in case. Thanks to everyone for the good advice.

 

This is exactly what happens, so it looks like my blend door is working....Thanks