Basically have the same issue winter or summer, Ac or heat. If you are going down the road nice air blows from the vents for say a 1/2 hour then its like some thing blocks the air flow from the fan and air just trickles out of the vents even though the fan is running full bore.

Thoughts?

Check for loose vacuum lines no luck.

 

the blend door motor coupler may be broken . look under the heater box on the passanger side by trans hump if you look close with the key on and ac/heater on check to see if the motor just keeps spinning .if so heater treater has a good fix take 1/2 hour to fix

 

My '03 did the exact same thing.....turns out, the system was low on 134 and the dryer was freezing up. System sounded like it was on OVERKILL but no air coming from the vents.............turn it off to "thaw out" for a minute or so and all was well after that.....until the next time.

 

Sounds like a blend door problem.Split year is weird My 98.5 has a different actuator than everything I could find on the forums. The "FIX" they sell doesn't exist on my truck. Mine turned out to be a broken vac line, in the hard plastic line across the firewall it was broken but you couldn't see it. Worked intermittently for a few weeks then finally quit all together. I found while tugging on the vac line fittings it finally pulled loose. A small piece of vac hose to splice the break and I was back in business. Any of the soft rubber fittings along the vac lines will cause the same problems if they crack.

 

You may also want to check the vac line starting point at the motor. There is a 90* rubber connection and the heat will crack it.

 

I don't think this is the issue as I have the same problem with heat in the winter.


I will try a new vacuum line and see if it helps.

 

First the AC compressor will run in defrost as well as AC depending on OAT but NOT heat, the only things that can cause an intermittent reduction in air flow are the evaporator core freezing up (most likely in AC or defrost) or the fan motor bearing is tightening up from over heating and will not spin as quickly, this is more common than you think. If the air flow is reduced from the "vents" and is not blowing out of the defrost then it must be one of those things I mentioned. BUT if it is blowing from the defrost while AC or vent is selected then it is a loss of vacuum. All air first passes through the evaporator core the blend door which is electric cannot reduce the amount of airflow it just diverts air through the heater core to "blend" the cold air with the hot to get the desired temp.

 

I should mention that when it happens you can not change were the air comes out of, it seems like it only happens when the truck is really warmed up.

 

........My 2001 does the same thing....i got the heater treater fix, but not installed yet...kim..........