Fuso inadequate AC system fixed

[Michel Szulc Krzyzanowski]

Before, I have mentioned AC problems with my Fuso FG expedition vehicle on this forum. The truck was bought new from Kearny Mesa Fuso Dealer in San Diego and every service the failing AC -system was mentioned. But every time Kearny Mesa Fuso Dealer in San Diego claimed nothing was the matter and even on this forum they lied that it was because the customer didn’t clean the filters.
How different is the truth. Found out thanks to Mitsubishi Fuso dealer So Cal in Escondido, California where my truck is now serviced. They checked the AC system and discovered that the cold air that enters the cabin is 30 % lower than the output of the AC system. They got in touch with FUSO USA who admitted they know about this problem. It is because the cold air from the compressor passes through the heat core and absorbs there heat from the engine. This is why that as of 2007 Mitsubishi has changed their AC system on the Fuso. FUSO USA also explained that they received many complaints about pre-2007 AC Fuso systems and developed a solution. The dealer will put valves in the AC-hoses so that the cold air goes directly into the cabin and bypasses the heat core.
To know: every Fuso from before model 2007 has an inadequate, poorly designed AC system.
There is a solution.

 

[kerry]

Can you elaborate a little more on the solution? How does changing the hoses change the route of the air thru the system? Did you have the solution applied to your truck? How much did it cost? Did it work? Can you post a diagram of the changes?

 

[kerry]

Ok, I've been rethinking what you wrote. Perhaps something has been lost somewhere along the line in translation. Is the underlying problem the fact that there is no positive shut off for coolant flowing thru the heater core when the AC is on? This would make sense to me. I've always thought that the temperature of the air from the vents has not been that cold. If that is indeed the problem, a manual shut off valve in one of the coolant lines should solve the problem. Maybe that's what you mean by valves in the line. If that's the issue it should be fixable pretty easily.

 

[biggoolies]

Will this come as a recall from Mitsubishi?

 

[mog]

To know: every Fuso from before model 2007 has an inadequate, poorly designed AC system.

Less one FG built in 2002. Mine works fine...at least to 95*F OAT.

I think I got lost there also.
The Fuso according to the service manual I have shows that the AC and the heater use the same ducting for distribution, as do almost all vehicles. While most of the vehicles I am familiarly with ‘shut off' the heater by shutting off the water flow to the heater core, the Fuso shuts off the heater core from the ducting system when selected to cold (blue). I confirmed this via the service manual, and a visual inspection on my truck (2002).

A simple check is to see with the system set to cold (blue), is that the air coming from the vents should be very close to ambient temp. If the ducting seals were bad, etc, then you could get bleed through of hot air. I would guess that you will have some heat just by conduction, even with the ducting valve closed (normal convection). If you have heat coming from the vents, regardless of the selector position then there is a problem.

A ‘mix' position is desirable for dehumidifying operation. This is were the air runs through the AC for drying, and then the heater air is added for warming. The Fuso has this as an operation option in the selector. AC switched on, temp selector set to the middle position.

A more positive shut off of heat would be closing off the water to the heater core, but you would need to review the system more, to make sure that does not effect the coolant flow adversely.

According to the manual the delta temp of inlet and outlet air is 18*F (10*C) AT 59*F(15*C) and only 9*F at 86*F. So not a lot of cooling at higher temps. Rated capacity of AC system is 14,300 BTU/hour, so you would think it would perform better. But there is a lot of glass in that front windshield. The Hottest OAT I've been in was 95*F, and it was fine in my truck.

So did your vents in the cab always put out hotter then ambiance air regardless of the selector position prior to the modification ?

 

[kerry]

Looking thru the service manual, it is clear that there is no valve which controls flow of coolant thru the heater core. It is always getting coolant flow. Temperature is controlled by which way the air blows thru the system. Most vehicles I have worked on control the flow of coolant thru the core so that when the AC is running the core is not hot. (I think). Adding a ball valve to one of the coolant hoses should be relatively easy.
Michael, is there any way you can confirm that this is the fix the dealer mentioned?

 

[kerry]

Looks like Mog was writing as I was. No, in mine the air on AC is cooler than ambient but nowhere near as cool as on my other vehicles. I will look closely at the coolant flow circuit when I have a chance to get to the vehicle. If blocking one line would have an adverse effect on coolant flow, it wouldn't be much more difficult to install a re-circulate system that bypassed the heater core using a series of valves.
Driving west on a hot day (90 degrees plus), the AC cannot keep up.

 

[mog]

If blocking one line would have an adverse effect on coolant flow, it wouldn't be much more difficult to install a re-circulate system that bypassed the heater core using a series of valves.

The service manual is not too clear, but a visual inspection shows that the Fuso system is like any ‘normal’ heater system were the coolant is shut off.

A cable operated shut-off valve from the junkyard (O-excuse me, an auto recycling yard…showing my age there) out of a 'regular' auto would work. Or you could get high tech and install an electric valve such as this one on eBay http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290558078007 (I’ve used this seller for the value on my Fuso pre-luber, great service) and then have it controlled by the normal Fuso control selector.

 

[kerry]

I was thinking a manual ball valve. My Bluebird has manual gate valves on all the heater cores.

14.5k BTU should be more than enough for that small a cab. Most RV's have a 13.5k btu roof unit. I use 8k btu to cool my camper on the FG.

 

[mog]

14.5k BTU should be more than enough for that small a cab.

That was my thinking also. The heater is rated at 12060 BTU/hour and it seems to work ok.

 

[Michel Szulc Krzyzanowski]

The cold air runs through the heat box of which the core is always hot. This affects negatively the temp of the cool air. Explains why as of model year 2007 Mitsubishi has abandoned that design. So Cal Mitsubishi Fuso Dealer from Escondido, Ca, installed valves in the hoses of the AC system so the cold air doesn't go into the heat box but directly into the cabin. Makes a huge difference. Only thing is that when warm air is required, the valves need to be opened. They are in the front of the truck and the cab needs to be lifted up. It is a simple solution that is of low cost that any Fuso dealer should know instead of pretending nothing is the matter and it is all the customer's fault (Kearny Mesa Fuso dealer San Diego)

 

[kerry]

Michel;
Any chance you can post a picture of the valves that were installed so we can mimic the solution?
Did you notice a difference in the AC once the valves were installed?

 

[haven]

Michel,
I enjoyed reading your blog, and I was disappointed when you stopped writing. Do you post news about your travels elsewhere? Twitter? Facebook?
Chip Haven

 

[Michel Szulc Krzyzanowski]

I'll make some pictures of the excellent work of So Cal Fuso dealer from Escondido and will post them here.
Not right now, so hold on.
The difference these valves make is impressing: highly recommended.

Chip, many people wrote me regretting I stopped with my blog in january 2011. Strangely enough, it still has over 40 visitors per day...
Now I publish a column on www.zone-10.com every Sunday: topic is photography.

 

[kerry]

One thing to keep in mind with this modification is that in the original configuration the AC was blowing across the heater core, cooling the engine. It can be expected that the engine will not run quite as cool with the AC on as it did when the AC was cooling the heater core.