1999 Ford Econoline V-10 6.8L dual air. Front air cool but not cold until moving at 40mph. When slow down air stops being cold up front.

For a previous rear air blowing hot only problem I just had disconnected vac hoses located and reconnected and A/C system evacuated and recharged.

Rear air works great now, but front air stopped blowing. Replaced resistor block up front, fixed that problem.

Now with rear air working great (even at idle) and with front blower motor control working great the front air is a little cool but not cold until we get going about 40mph, kind of like with my other cars where freon is low and whole system does not cool well until at speed.

So with nice cold rear air I doubt the freon is low and I don't want to add more and blow the thing up.

I've read the blend doors are electrical so maybe the front blend door is not going all the way to cold side? Not sure why it suddenly would at speed though.

Thanks for any insight.

Yes, the blend doors are one source of a problem but you can easily determine if that is the problem by pinching off one of the heater hoses.

I would guess your problem is likely a plugged orifice tube in the front but double check that the cooling fan is pulling enough air also. If the tube is plugged, it's a good indication that the compressor is coming apart and that could be due to a cooling fan problem.




78 Corvette Pace Car For Sale-18k mi orig-Florida

Too add to already good suggestions by Hammer Time: In most dual air systems the rear is an expansion valve and can hog the bounty of liquid refrigerant to expand vs an O tube which is crude in comparison. Air flow from clutch must be excellent and no leakage of hot coolant to front as mentioned.

Pressures would help with just front A/C operating at full, at a raised idle. If pressures are low - leakage is the common issue and determining what to do, boost or fix a leak depends on results of testing.

BTW - If heater and A/C are in battle the heat wins all the time,

T
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Tom Greenleaf - MetroWest, Boston

Thanks Hammer Time and Tom.

One of your points to clarify - regarding HT and the "cooling fan is pulling enough air" comment and Tom reference to clutch - you are suggesting the radiator fan is not spinning fast enough? Suggesting the fan clutch might be slipping and allowing fan to run slower than it should? How would you test that? Bearings in the clutch not loose or noisy, and the engine does not run hot after idling 10-15 min.

I took about 20 mins driving around the neighboorhood about 20mph testing if having the rear air off caused the front air to be colder. Front air is colder with rear air off. Sounds like Toms idea of the rear unit stealing gas from the front unit.

So would adding some more refrigerant help this problem? It's a big system, maybe a half pound?

I did not try clamping a heater hose yet to see if I have some hot air coming into the front but I will.

Thanks! Tim

Quick re-read so sorry if I'm missing something.

Fan clutch on a van should be OE an HD style with a bi-metal spring which needs to be clean. From heat it allows fan to pull like a Cessna taking off and at speed of vehicle air flow is sometimes enough.

IMO - fan clutches are losing 10% per year in efficiency. If known 5 years old or older it's probably compromised already.

DON'T ADD REFRIGERANT TILL YOU FULLY UNDERSTAND IF IT NEEDS ANY!!!!! Overdoing it causes more trouble and hair loss than taking the time to understand it!

Top of this section is a good discussion on charging a system. Worth the read and know links were not yet on line when posted.

Air flow allows for refrigerant to condense to a liquid to be evaporated later at the right place and time. When and if compressed gas doesn't allow proper amount of liquid to return thru system it will suffer and more-so with dual A/C as rear will hog the bounty as said. Once front alone can operate properly, then you can blast the rear and pressures can go nuts so outputs vent temps are an important observation. Don't guess - measure the temps!

You can mist the condenser with water and watch for results. It will almost always perform better but if that trick totally corrects outputs temps then you need to dig into diagnosing why if extreme. No automotive A/C should be too low on charge or too high. It really wants to be just right,

T
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Tom Greenleaf - MetroWest, Boston

Just to add to Tom's explanation on the fan issue..... If the radiator fan is not pulling sufficient air across the condenser, it will increase all the pressures which not only will reduce cooling but lead to premature compressor failure which could be what caused the blockage in the orifice tube, assuming you have one.

My suggestion would be to have the system professionally evacuated, replace the orifice tube and accumulator and recharge the system with the proper amount of charge and see what you have for pressures then.




78 Corvette Pace Car For Sale-18k mi orig-Florida

Totally agree - near all later Ford products use an O tube or CCOT system. Debris is found needs evaluation if clogged,

T
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Tom Greenleaf - MetroWest, Boston

Just to close this one out - if I run the front air for a few moments before turning on the rear air then the whole system works reasonable well for such a huge interior (15 pax) in hot, humid S. Florida.

Thanks for the help guys!

Tim

Appreciate the followup Tim,

T
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Tom Greenleaf - MetroWest, Boston