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Old 07-09-2016, 11:04 PM   #1
Join Date: Oct 2015
Posts: 32
Can someone explain how the F53 A/C system works? Especially hot/cold air mix

I have 2001 Itasca (F53) and I'm having issues with getting consistent cold air. I'm 95% sure it is not the actual A/C system (compressor, etc), as the coolant level is right, the plumbing is cool (low side, hot high side) and compressor is running.

It blows fairly cold air, but it seems to get warmer as motorhome warms up. I just tested the vents and got 53F deep inside the vent as the lowest reading with an ambient temp of 90F (actually a little warmer inside than out) after about 5 minutes or so of starting. This was outside at night, during the day it is much hotter and the vent temp is much hotter understandably. I realize a 40 degree spread is decent if my infared thermometer was accurate, but when my car with black interior is outside all day the AC can make your hands cold holding it up to the vent before the car cools down, so I think there is room for improvement which is why I want to learn more about how the system works.

About 10 more minutes the lowest reading I could in the vent was 63F. You would actually think with it being on Max AC with it recirculating air cooler than the outside (once it cooled off a bit up front) it would get colder.

I checked the two hoses going to the airbox that is on the passenger side of the engine bay before starting the motor while it was cold. They were both 106F. I presume these are the hoses that go to the heater core for when you want heat.

After I got that 63F vent reading I went and checked the hose temps. The forward hose (closest to bumper) was 138F and the hose behind it was 168F. I was suspecting maybe the heater core was heating up and my cold AC was going across it and losing some of its coldness. The ambient temp of the engine bay near the hoses was 118F, so I presume some water, if not full flow, was going through the hoses.

So here's the question... does this design have the heater core inline with the ducting that the cold air passes through? I think some car A/C is setup like this and the system shuts off the hot water coming from the motor so it doesn't produce heat that would warm you cold air. I believe others are setup so they only flow air past the heater core when heat is selected.

If this is the type of system where the cold air always flows past the heater and it is suppose to block water flow from the heater to prevent it from heating then I must have a failed valve to some extent since it surely looks like heat is entering the core.

If not, then it might just be that this is the best I can expect from the A/C, but then again it is weird that A/C gets warmer as time goes on. I suppose another possibility is I have broken, cracked or mechnical baffle or something that is allowing hot air from the engine to mix with my cold air.

In fact, I write this that might be a real possibility because when I run outside air (no A/C, vent only) it is always pretty warm even with it is really cold outside with the dial selected to full cold. I know the dial must be working to some extent because it gets really hot if I put it to full hot.

It could be a baffle with the temp control, but again I'm not sure how it works. Is the temp control regulating the amount of hot water going to the heater core or is it regulating the amount of hot air is mixed with the cold air (two different intakes, just mixed base on a baffle)?

I know this is turning into a long post, but I will through this out there also. I have a slight vacuum leak but from what I understand it shouldn't affect what I've described above since it only controls the vents (defrost, recirc, etc). When I first start it up if it is on Max recirc it will blow out the defrost. If I switch it to regular AC it comes out the right vents and then I can switch it back to Max recirc and will stay. If the engine is under a heavy load it will go back to the defrost vents and when I let up and coast it goes back to proper vents. I suppose perhaps it could be letting some outside air in but I don't think this is the case. Either way, I want to fix this also so it is at least one more thing to rule out. Can someone tell where to find the vac lines? Do I need to get into the dog house? I flipped the dash up and didn't see any vac lines. It appeared all of the lines coming from the AC controls were electronic.

Thanks in advance for your feedback!
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Old 07-10-2016, 12:40 AM   #2
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The dash A/C system is installed by the coach manufacturer and could be from one of a few HVAC system manufacturers . Evans Tempcon and Denso are common .
I have the Evans system with vacuum controls and an electronic water shut off for the coolant flow through the heater core.
Many owners have added a manual shut off to the heater hoses to boost the systems operation as I believe the air flow goes through both the A/C evaporator and the heater core before entering the coach.
If your system , reverts to defrost on hills then it's vacuum controlled as defrost is considered a preferred for safety, air flow if the vacuum system fails.
I have a vacuum schematic for Evans systems but it is next to useless, as it shows only the line colors , not how and where they are installed.
In your case you may have a bad check valve between the engine intake manifold and a vacuum reservoir that is meant to hold the vacuum up for the pulls on hills ; but in some cases the vacuum reservoir is simply too small and I had to add a second reservoir on a P/U truck for that reason.
Can you post a picture of the back of the A/C controls and the heater hoses where they enter the fire wall ; if I can see what your working on maybe I can provide some help.
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Old 07-10-2016, 07:22 AM   #3
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Does the temperature rise you're noting take place while you're driving, or just sitting still?

It's worth knowing that the F53 only has a clutch driven fan that engages when the air passing over it gets hot. This means that when sitting still, unless the coolant heats up the air the fan it doesn't engage. This can let the AC system warm up as you describe.

I'm guessing you've noticed poor performance while driving, but are maybe measuring things sitting still. Could be skewing your data.

And I believe a 2001 Itasca would have used an SCS Frigette HVAC system. They went out of business a few years ago, but reemerged/taken over by/something as Victory Climate Systems.

Also found when I searched here for SCS Frigette info.

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Old 07-11-2016, 10:11 AM   #4
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The fact that the water temp in the heater is dropping 30 deg. sounds like you are cooling the water. I would think a 5 deg. drop would maybe OK, but thirty deg. seems a lot. Most,if not all, AC systems have gone to blend door heating and cooling. Some are going to advise you to put a water shutoff valve in the water line. Ford has sent out Service Bulletins saying NOT to do this. During warm up of the engine, the coolant is still going through the heater. It must not be stopped (according to Ford.) It sounds like your blend door is not completely closing. I would check this first. Installing a curtain rod and curtain just behind the drivers and passenger seats worked very well for my customers.
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Old 07-11-2016, 10:30 AM   #5
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bizee, your 2001 Itasca has a separate AC cooling coal and a separator heater coil and a blend door to control the output temperature. Item 3 in the attached drawing.
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Old 07-13-2016, 11:33 PM   #6
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Wow, thanks for that drawing, that is my unit for sure!!! Did you find it online and if so do you have a link where you found it if there are more drawings, I would like to see if I can glean my info from it.

As I mentioned there are two tubes to the heater core. The one closest to passenger was hottest. I took a C-Clamp to pinch it off thinking that would be the inflow from the motor. It didn't help anything, still not getting as cold as it should, no difference.

Oddly though, the tube was the same temp (168F) on both sides of where I pinched it off and the other cooler tube was still around 145F. I guess I should try pinching off both just to be on the safe side next time.

I did locate my vacuum leak, but I haven't solved it. I was mistaken thinking the vent selection controls were electronic. The small colored tubes looked like electrical wires on first inspection.

I turned the air off so I could listen for leaks and it is leaking at the control itself. There is a clear green silicone-like boot on the back of the control that all of the vac tubes plug into. That boot does not have a perfect seal with the back side of the plastic control. I tried holding it tight against it the control and it reduced the leak, but I could still hear it hissing a little. I'm not sure the best way to attempt repairing it. I've considered putting some silicone all around the boot and seeing what happens.

What I really want to do is get inside that airbox so I can see what's going on and make sure the air mixer (hot/cold) is working right and the mixer for outside ambient vent vs AC vs AC Recirc is working right.

I have a feeling that one of the mixers/baffles is either cracked or not fully going into place. Or it could be the heater core is heating up, or a combo.

Have you ever opened up one of those boxes? Looking at the diagram its hard to tell if I can monitor if the mixers are working right or not with it opened, but I won't know until I try unless someone else has been down that road before.
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Old 07-14-2016, 09:08 PM   #7
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bizee, here is the link to the Winnebago manuals. That picture came from the parts catalog for your coach.
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Grant & Pat
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Old 07-15-2016, 12:24 AM   #8
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Ok thanks, I didn't realize all the 3rd party parts were included in there. That is a big help.

So I've spent a while troubleshooting this and I'm hoping some of this rings familiar to someone once I describe the symptoms.

When the rig is first started cold with ambient temp around 100F (night time) the vents quickly get down to as low as 50F. This is actually reasonable to me if it could stay that temp.

As the engine warms up the air warms up. I know this could be somewhat do to sitting stationary, but I when I tested it yesterday driving the temp did not get colder.

The air warms up to 75F.

It could be do the heater core not shutting off, but yesterday I pinched it with a clamp on one of the hoses and didn't notice much difference. I think it may have to do with the warm engine air heating up and some air being drawn from outside and/or across the heater core.

I tracked down the vacuum leak. I found it hissing right at the dial selector (vacuum selector), the actual dial that controls Max AC, AC, Vent, Defrost, etc that all the colors vac lines are plugged into.

The reason I didn't notice it at first is because it only hisses when the dial is in the Off or Max AC selection. I determined that vac lines that are leaking off that controller are the blue and black lines by pinching them off and observing the hissing stops.

I initially thought it was the green silicone rubber like boot/diaphram that joins the rigid plastic plugs to the hoses was the culprit, but I'm not so sure now. I think it might be in the plastic selector itself where it doesn't fully seat or however it seals when it is in certain positions. Pressing the boot firmer against the plastic didn't seem to change the leak much.

Another thing I noticed is switching between AC and Max AC didn't seem to do anything aside from stopping the hiss of the leak. In other vehicles usually switching to max AC makes it louder or blow harder and the air gets cooler. None of these happen.

I'm left with one a couple options left on whats wrong...
1) The regular AC mode works as it should and 75F is the best it can cold outside air going past the motor bay that might be as high as 125F+. Max AC is not recircing as it should, and hopefully by fixing the vac leak that will fix it and all will be well.

2) There is a problem with blend door allowing hot air from the heater core into my mix and/or the heater core is not shutting off so it is heating my cold air.

I need to figure out how to fix that vac leak. I am going to try to source the part from the links provided. My google-fu turned up nothing for it. But since we're leaving soon I'm hoping to find a DYI fix by trying to seal the boot with silicone or dissemble the switch to see if I can find the culprit. I'm just a tad hesitant if I break it that we'll be really SOL. I'm hoping someone is familiar with this switch and can give me advice on if it is serviceable.
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Old 07-15-2016, 12:42 AM   #9
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I was able to find the part. I'm going to see if I can get it expedited here.

Looking at the drawings it makes it look tough to examine the operation of the vac motors/servors/doors while under operation. I am going to just start taking it apart and trying though.
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Old 07-15-2016, 07:14 AM   #10
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Best of luck in fixing your AC. I know my door that closes when in max ac that blocks outside air from entering to just recirc cabin air, was closing but the gasket was so bad that it may as well been open. I used some padded headliner material to cover the door and works much better.
Have you traced your vacuum line from the intake manifold to the vacuum reservoirs? I have a large one (the size of a small loaf of bread) down by the right front wheel well, the second (the size of a softball) up front by the ac box. All vacuum lines need to be in good working order.
I too have added another heater hose cut off valve to ensure no hot engine coolant warms my cold air. I fear the other door may have bad gaskets also.
Hope this helps and happy trails.
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Old 09-05-2016, 09:22 PM   #11
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I just went through similar with the system on my 2001 Adventurer which should be very similar to the Itasca on the F53 and found 2 issues with the system causing vacuum loss.

1 - The blue hard emissions tubing does not hold up well to the weather its exposed to under the hood and tends to perforate for most of its length even though this may not be very visible or make a noticeable hissing sound. I could only get black 1/8 inch OD hard emissions tubing locally in 3 foot lengths which I joined using 1 1/2 inch long sections of 7/64 inch ID rubber vacuum line marking it every few inches with blue tape. The line on mine exits the dash under the computer desk so I ran it from the valve on the Frigate unit under the hood up under the computer desk and spliced it into the good blue 1/8 inch hard tubing where it can easily be seen several inches from the control under the dash.

2 - The soft rubber 1/4 inch ID vacuum tubing coming off the back of the round vacuum tank under the hood on the drivers side was getting low vacuum. This line transitioned to red 1/4 inch OD hard emissions tubing inside a black wire loom behind the vacuum tank and ran behind the Ford power distribution box and then headed toward the passenger side valve cover however it went down to the frame rails below instead of following the bundle and ended up at a larger vacuum tank nestled behind the front inner bumpers steel frame. On the inlet side of this tank is a short piece of rubber hose to make the connection to the inlet of the vacuum tank that disintegrates and leaks badly especially when the engine heat in that area builds up which can be replaced with a 1 1/2 inch section of good quality 7/32 inch fuel line.

Dealing with these two vacuum losses made for more positive operation of the flappers in the Frigate unit and provided much more consistent cooling.

The green hard tubing did not appear to get as badly damaged by being exposed under the hood however I will be keeping an eye on it. Anywhere this hard plastic bright colored tubing is exposed to light is a potential failure point. The seam where it is joined as it is shot out of the extruder when its made appears to be it weakest area that when exposed to light or weather can allow this type of tubing to split along its entire length.

Note that the diameters may not be exact except for those involving the 1/8 inch hard tubing and may vary.

I did have to also top off the refrigerant a bit and the AC blew icy cold during the 1 hour test that followed while outside temperatures hovered in the 90's in the noontime sun.
Neil V
2001 Winnebago Adventurer WFG35U
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