Are you sure? I'm pretty sure the full flow of coolant runs through the core at all times (except when the valve is closed on Max). The blend door is partially opened/closed to heat the air.

Joe

 

And also of interest is if they changed either the AC engagement clutch or the compressor to accommodate the more frequent on/off cycling if the temp is controlled by cycling the AC.

I use US Gear gauges and exhaust brake, and a number of years ago they came out with a package that used an AC clutch in place of the OEM viscous one for controlling the fan. The idea was to eliminate the parasitic HP drain when the cooling fan wasn't needed. Well, it work well until the clutch started failing from not being able to stand all the on/off cycling, and I fear doing a mod to cycle our current AC clutch might be asking for a similar failure.

 

Cant we get the set up of a Crown Victoria or Lincon. My Dad has a Lincon and if you put it on 68 or 72 degrees it keeps it that way. But he's got a lieometer too!..

 

If that's the case, the design should be in a category that's much worse than just "Dumb#$%" as suggested by nlemerise, as it implies I've been using the AC to cool the full flow of hot coolant as well as myself. I figured that with the temp **** set to the coolest position, I was only using the AC to cool a trace amount of hot coolant, and most of the cold air was for me.

 

I would agree, my guess is the heater core will put out much more btu's than the evaporator coil can remove.

 

If you look at how the blend door is done, it would make more sense to you. I used to have a drawing of the one for my Ranger someplace -- let me see if I can find it...

Joe

 

Found it:


I'm assuming ours is similar in design. I *am* sure that the coolant valve to the heater core is either open or closed, though. Go look at how it operates -- when you select MAX (and I believe off), it closes. If you then select anything else, it opens regardless of temp dial setting...

Joe

 

You are correct Izzy...what I meant, but clearly didn't say is that the cold air is just tempered by the hot air over the core usingthe blend door and the dash **** to control it...still a dumb$%# design, imo.

 

That is the $64 thousand dollar question...What I am thinking is do a mod which closes the hot water flow (either a vacuum valve as I have, or a manual valve). Then use a thermostat out of something to control through a relay the compressor clutch engagement/disengagement. This would be a major fuel saver in my opinion . The worry though is that the clutch on our system may not have been designed for cycling so many times...then fuel mileage savings would be eaten up by compressor or clutch failure . I'm out in the sticks so getting to a parts yard is difficult, but I am beginning the investigation of auto air-conditioning systems to learn the control methodology.

Anyone have air-conditioning expertise, please wade in here...your knowledge is needed!

ON EDIT: Check this out...this is the AC cycling switch -



Can someone with way more AC knowledge tell me if you ran the lead from this switch (the one that currently goes to the clutch) to a thermostat in the cab, then to the compressor clutch (via a relay) if the mod wouldn't work? Our compressors cycle, but they cycle solely on internal pressure, not having anything to do with cab temperature or dashboard setting (which releives my worry about clutch cycling failure). I'm trying to figure out why you couldn't have both to cycle the compressor (system pressure AND cab temperature). So it would work as follows. Set the new thermostat inside the cab to a temperature lower than ambient. If the system pressure is high the AC cycling switch closes which allows current to flow to the thermostat, which then lets it flow to the clutch. If the thermostat opens the clutch disengages OR if the system pressure falls, the clutches disengages. Come on electrical and/or AC people...help!

 

Well, the super-delux thermostatically controlled system in the high-end vehicles work like you describe (they were optional in the 150s for sure and my Dad's Navi has it, but I haven't been in a SuperDuty with one). You set a temp and it cycles the compressor/adds heat as necessary. Seems like the compressor is nearly always running to dry the air. Maybe this is the system y'all are talking about??



Joe

 

Some SD's have that system, when I was looking to buy F250, I saw few (1 or 2 out of hundreds) with automated A/C.

 

You know what is interesting? All my research to date indicates that most thermostat controlled air conditioning systems in autos actually control the temperature by using a pump & valve in the hot water line to the heater and an infinitely variable fan control. In other words, they leave the compressor alone, let it cycle by system pressure and either speed up (when you want it warmer) or slow down (when you want it cooler) or stop the flow of hot water (if you want maximum cold), at the same time the thermostat tells the fan how fast to run based on the difference between ambient temperature and what you set the thermostat at (small differences give slower fan speed, larger differences speed the fan up). But what I have found out is that people have adapted home thermostats to control RV air conditioner/heater systems. I have read that 24vac thermostats run just fine on 12vdc...this means to me, that in theory, a thermostat exists which will control the compressor.

 

Nice pic Izzy, so it looks like the temp **** varies the position of the "temperature door" via the "blend door actuator". It appears that the "warm" position, which is shown dotted, completely shuts off direct access to the evaporator core, and the "cool" position allows full access, but If I take that diagram literally, it looks to me that in the "cool" position there's as much or even more access to the "heater core" than there is in the "warm" position? However in the "cool" position there's not any direct flow through the heater core, just access to residual heat. Also, in the "warm" position the air must first flow through the evaporator core and then the heater core to get to the cab. I hope this doesn't mean that the AC is used in the winter to help control the temp?

Now, do I have this part correct? I'm assuming that these doors are all spring loaded to stay in one position, and then the vacuum pulls and holds them to the other position? It looks like all the doors are in the positions shown as solid black when vacuum is applied to a line? So the "outside-recirculate door" closes off access to the outside in either MAX AC or OFF? So if you stop the truck with the mode switch in any of the other positions the door to the outside is open which lets in fresh air (as well as mice). I guess if the truck sits too long the vacuum bleeds off and the door opens anyway and mice can still get. Also, the big mystery bang is due to the door slamming shut after starting the truck and building the vacuum again!

I checked my new Haynes manual, but it doesn't have much on the AC as they have a special manual for that. However, it did have a pic of the back side of the control panel, and it was very clear that only some electrical wires are hooked to the temp ****. Therefore, that **** must control the setting of an electrical type thermostat for varying the position of the blend door. Also, there's a two wire connector on the AC clutch. Maybe it might be possible to use the existing thermostat and make it do double duty. I'd like to see a diagram that includes the coolant valve to the heater core to see for sure when its open or closed.

 

I'll try as best I can to answer... I'm not sure how tight the blend door closes one way or the other, but the drawing would make one believe that it doesn't close all the way off. Also, it depends which setting you're referring to. When set to just vent or floor only, the compressor is off so the air flowing through the evaporator isn't cooled. When set to bi-level, defrost, or floor/defrost (and both AC settings obviously) the compressor runs so the air is dried in defrost, and cooled for bi-level operation.


If you look at the drawing, there are tags. V=Vacuum, NV=No Vacuum, and PV=Partial Vacuum. And yes I hear the door slam closed when my truck starts, too. Don't know about the mice thing -- I thought the fresh air intake was under the little grill in front of your windshield?? Never looked...


I'm not sure about that -- all my experience is with the Ranger & Bronco, and even then it's limited. I never had to mess with the back of the panel, but a guess would be that when set to fully hot, it disables the compressor.

I like to old style controls like my Bronco had -- there was a small slide controller for recirc/fresh air (mine was almost always on recirc) and a compressor switch so you could pic whatever combination you wanted (compressor was almost always on, since it's usually hot/humid in FL).

Joe

 

Neal,
It seems to me that it should work fine to turn the compressor on or off (so it doesn't get too cold in there), but having just been on a few nice long drives, I simply turn the fan speed up or down to control cab temp, and the system stays on Max.

What would be *really* nice is if the Premium Climate Control system could just replace the stock system with the same (or very similar) connections. I'm curious if that is a dealer option or does it have to come from the factory with Premium CC? If it's a dealer option, I'll bet it would be a fairly easy job to put one in.

Joe