Well, I recieved the Excursion heater core valve; It is a Motorcraft # YG-275 It looks like a typical coolant valve, about 3" tall, with 5/8" inlet on one side and 5/8" outlet on the other side (about 3/4" lower), with the vacuum port on the top. It is normally open and closes the coolant passage upon application of vacuum.
Now, I have to decide if I will install it now, or wait 'till my warranty is over... I'm satisfied w/ the a/c cooling, but my problem is that the vent air is warmer than the outside air, making me either run the a/c or open the windows on days that are not really that warm. Also, after I restart the engine after being parked for a short time with the engine hot, I get a blast of hot air out of the vents. I presume that the hot water in the htr core heats up the inside of the plenum.
What I need to find now is a 12 Volt operated vacuum valve- preferrably from some other common automotive application, so we can easily get it at a parts store.

earlier I wrote:
> .....According to the light truck shop manual, the Excursion w/
>aux heat/ac has a vacuum operated valve inline with the
>heater core. The valve will block coolant to the heater core
>when the control is set to "max". I checked the parts
>catalog and sure enough, one is listed. I have ordered one
>from carparts.com so I could see what it looks like; I'll
>let you know what it looks like when it comes.

 

Let us all know the cost of the valve, and where we can get one.
That sounds like the "safest" way to go.

 

The valve will help, but it's not going to make enough of a difference for you to notice much, the system is still under charged.
For instance, my 2002 Explorer had a problem from the factory with that very valve. The vacuum switch that operated it was mis-aligned and would not send vacuum to it when I went to "full cold". I rerouted a vacuum source to it so that it would operate when I went to "max a/c". It did a little for the outlet temps but not enough for my wife to notice, yes, she's mad about the system in this vehicle.

 

>Let us all know the cost of the valve, and where we can get
>one.
>That sounds like the "safest" way to go.

I paid about $14 at carparts.com They seem like a pretty good place to get parts on the net, the shipping charge was reasonable, and no sales tax. You could go to your local parts store and ask them to cross reference the # if they don't sell Motorcraft, or try the dealer.
mike

p.s Anyone know where I could buy one of those Air Valves that look like a toggle switch?

 

OK, I read thru most of these posts. I've been working on a/c and refrigeration for years. Used to work on the refrigeration in Cray Supercomputers so.....I have some knowledge.

I just bought a 2002 S/D Diesel, Crew cab. I also noticed the same problem as is mentioned here. Here's what I have tested so far:
1. Using a digital temp probe which will show me .10 degrees diff, monitoring the outlet air in max a/c fan speed 3 I also get down to maybe 46 degrees on a 90+ degree day here in Houston. I see the temp vary about 1/2 degree. When in normal a/c no variance but the temp is a couple degrees warmer.

Comment, this is completely unacceptable. Max a/c should blow much colder then normal a/c.

2. Monitoring the suction pressure, at the accumulator, I see that the pressure works it's way down to 20 degrees and the low pressure cutout switch cuts out the compressor. Soon as the pressure rises, it cuts back in. This is what's happening to anyone with a 2002 and maybe 2001 model truck, with CORRECT charge. My friend has a 2001 or 2000 Ford Crew cab and his suction pressure goes down to 15 and it still doesn't cutout, I'm wondering if they changed the low press cutout setting.

The reason the temp is not getting any lower then 46 or so is due to the suction (low) pressure getting too low, 20 degrees, and cutting out the compressor. The reason the switch cuts out at 20 is to avoid freezing the coil and also slugging the compressor with liquid.

Why is this happening? Take a look at the condensor on the 2002 and maybe even the 2001. The condensor coil is the one up front of the radiator that condenses the hot gas coming off the compressor to a liquid. The condensor is much bigger then the one I had on my '96 extended cab diesel. I think they went to the bigger condenser to help with lowering the temp when at idle.

I come to these conclusions after I convinced the dealer yesterday to pull the liquid line apart and check the orifice for clogging. It wasn't clogged. Today I decided to do some more tests. I pulled off the wire harness connector going to the low pressure cutout switch in the accumulator and jumped it out so the compressor would stay running. I did this to see just how low the pressure would go, guess what, it only went to 20 psi on a 93 degree day. So what that tells me is exactly what Alan said, I can add a little more freon, above the 2lbs & 10 oz the label says. What this will do is raise the pressure enough to keep the low side above 20.

What I have to experiment with is how much extra freon to add. I don't suggest anyone adding a pound because I don't think we need to add that much extra, I'll experiment. The problem is that on a hot summer day, if I add say 6 oz and it doesn't cutout, it still may cutout when the temp outside goes down to the low 80's. This is because the outside temperature causes the hi side pressure to decrease and in the case of an orifice type system, the low side pressure will drop also.

I think ford got too carried away with the size of the condensor, keeping the head pressure too low and consequently, the low pressure too low as well. There is no temperature drop across the accumulator either so that isn't causing the low pressure. As Alan stated, the symptoms are of a restriction in the low side but it appears it is because of too large a condensor. This leads to another suggestion which is to block off some of the condensor with some cardboard or something.

I'll let you know what I eventually determine as a decent fix.

I wouldn't fool around with the heater core idea, not worth the hassle. Will get back to you.

 

Just a couple other quick comments, this is definitely a problem with the design of this system. The problem could also be that the orifice is a little too small. The purpose of the orifice is to drop the pressure of the incoming liquid so that it will boil off and pick up heat. If it is the orifice, that's unfixable unless we could get some specs on the orifice opening sizes for different year vehicls and find one just a smidgin bigger. If the orifice was a little bigger, then the pressure in the evaporator would be higher which accomplishes the same thing as adding more refrigerant or blocking off some of the condensor to get the pressure up.

I'm almost leaning toward blocking off some of the condensor to raise the pressure a little which would keep from overcharging and slugging the compressor on really cool days. Remember too that when you are running the defrost, the compressor is running as long as the ambient temp is around 55 or higher. I don't know the exact temp for cutting out the compressor on low ambient temp. Ambient is outside temp.

Problem with blocking off the condensor is you also block off air to the radiator so I'll have to look at it.

 

Not sure if anyone is still following this thread but....
I did some more checks on my a/c system. Blocked off half the condensor and the compressor still cycled off and on in max a/c.
The cab temp was 74 degrees so it was pretty cool. So blocking off the condensor is not the way to go.

I then added about 8oz of 134 and it still cycles. For instance today it was 75 degrees and the compressor was cycling on normal a/c.

I truly think that the way to fix this problem is to use an orifice that is a little bigger and reduce the amount of charge to keep from slugging the compressor. Problem is I don't know if an earlier model year orifice will work and if it is any larger in size.

One thing I'm curious about is if anyone knows what the low pressure cutout switch should cutout at. I'll post a new message just in case nobody is following this thread anymore.

 

 

I have found the ultimate solution for the heater shut off valve. This eliminates raising the hood and manually opening or closing an in line valve. It is an electronicly controled heater valve, including wiring and a switch. It is universal for 12v applications, and has 5/8" hose connections. What I intend to do is: Remove the cigarette lighter assembly (non-smoker) and use the existing wiring to power the switch. The switch assembly looks like it will fit nicely with minor modification (could even get a Ford ****). Cool!

http://www.fix.net/~mbarrett/valve.jpg

super duper

1999.5 F250 XLT SuperDuty SuperCab ShortBed 7.3L PowerStroke AutoTrans 3.73LSD 4X4