I apologize if someone has already covered this, but I've searched the forum, and I can't seem to find anyone who has addressed my exact issue.

The original start of this problem began probably 3 months ago, and it literally only happened a handful of times over those 3 months, but since I replaced my blend door actuator about a week ago, the problem has gotten rapidly worse.

Basically, one day I was sitting in a drive-thru and had shut my truck off to order. When I turned the truck back on, the A/C was blowing hot. I shut my truck off again, and when I turned it back on, I was conscious of the "thump" from the blend door, and the A/C went back to it's normal ice-cold status. This happened maybe once per week or once every two weeks for the past 3 months in similar scenarios, so I decided that it must be a blend door actuator problem.

Last week I installed a new blend door actuator, and now I have much worse problems than before. Sometimes the A/C will be hot at idle, and sometimes it will be cold. Sometimes it will be hot at 1500+ rpms, and sometimes it will be cold. There seems to be no reasoning behind it whatsoever. Usually if I cut the A/C off for a few seconds and cut it back on, I can hear the blend door thump and it will be ice cold again. Sometimes I don't need to shut it off at all. I will just randomly hear a thump, and it will come back on. It also doesn't seem to matter what the engine is doing at that point. It will thump and come back on just as randomly at idle as it does with high rpms.

Is it possible that I was just unlucky enough to get a faulty replacement blend door actuator, or could it be something else I'm not thinking of?

I don't believe the clutch is slipping, and the gap is good. None of the lines seem frozen, and I have no condensation on the floorboards. The blower motor is working fine, and I have no problem directing the air anywhere I want it. My coolant level is good, and since it sometimes gets hot at high rpms, I don't believe that the condenser is the problem.

Is there anything else that would be making the thump that I'm hearing besides the blend door? Is the blend door purely controlled by the blend door actuator, or is it controlled by the actuator and the clutch? If it's controlled by both, then maybe the clutch is slipping after all. Is there any sort of hinge or something on the blend door that needs to be oiled? The fact that it's cold so often, especially at idle makes me think it's pretty unlikely that the door is broken. I live in the freakin' armpit of hell in Texas, and we still have many more weeks (or months) of hot weather to go, so I really need to figure this out. Any help will be greatly appreciated.

One more thing I should mention: I live in an area directly affected by Hurricane Harvey, and I had to drive through high flood waters quite a bit making deliveries. Is there any chance that moisture is caught somewhere and causing these problems? It seems fairly unlikely since, as I said, I live in hell's armpit, so one would think that it would have evaporated in like 10 seconds. Haha.

 

This sounds like a vacuum leak to me. Have you checked the hoses from the vacuum pump?

 

Could also be a damaged/failing vacuum pump. You said you drove through flood waters. The vacuum pump is on the passenger side inner fender, close to the heater/evap box. It could have very easily taken a few gulps of nasty water and be in the process of failing.

 

I haven't checked them, but I will! I've owned quite a few 7.3L, and to be honest, the a/c has always been something that illudes me a little. If it's a vacuum issue or vacuum pump issue, wouldn't that cause me to lose freon? Because I don't seem to be losing any. I'm sorry that I'm so confused!

 

Thank you! I will check it!

 

The vacuum pump does not have anything to do with the actual operation of the AC. Vacuum is only used for the ESOF hubs (if equipped) and the actuators FOR the AC blend door(s).

 

Gotcha. Thank you!

 

Do you happen to know if the blend door and ac clutch are connected in any sort of series? For example, does the clutch engage and then the blend door closes or vice versa? The reason I ask is because I finally got stopped while the air was blowing hot and popped the hood while it was still blowing hot. Up to this point, the cold air has always started again before I have a chance to look under the hood. The clutch was not engaged. I got back in the truck to check the blend door, and as soon as I opened the glove box, the blend door thumped, and cold air returned. The clutch was obviously engaged after that happened, but I don't know which happened first.

 

The blend door is vacuum operated and has nothing to do with the operation of the AC clutch, which responds to the demands of the AC thermostat/controls. Sounds to me that your AC clutch needs to be adjusted properly if the rest of system is operating properly. Proper freon charge is a possibility as well.