1998 A/C air flow reduces to almost nothing
 

The a/c in my 1998 Silverado works great for about 20 minutes. Then the air flow out of the vents goes down to almost nothing. The fan is still running. Switching the fan to high makes lots of noise, but almost no increase in air flow. I switch to defrost and other settings and there is very little air from those vents either. I notice that when I shut the truck off, there are always several gallons of water (estimated, but lots in any event) that drains from the expansion coil drain on the firewall. I speculate that a high level of water is building up in the coil enclosure and is somehow blocking air flow thru the coil. Is this possible? How would I fix this?

RE: 1998 A/C air flow reduces to almost nothing
 

Welcome to the forum!!! Sounds possible. Never done much with AC, but someone here should be able to help, just hang in there.

RE: 1998 A/C air flow reduces to almost nothing
 

check ALL your vacuum lines under the hood. especially around the firewall near the master cylinder and by the steering column, orwhere all the wires go through the firewall. i had this problem once and it was a loose vacuum line. the a/c dampers for the air flow is controlled by vacuum.

:)

RE: 1998 A/C air flow reduces to almost nothing
 

pegleg45, welcome to the forum!!!

RE: 1998 A/C air flow reduces to almost nothing
 

This also sounds like the system is freezing up. When it does this, what happens if you turn the system over to heat and put the blower to high? Try this next time and turn the dash vents on. If the system is freezing up, you will get a lot of vapor blowing out of the vents in just a few seconds as the heated air thaws the ice, and the flow will be back full strength in just a little bit.

Freezing would also explain all the water draining out, especially if it takes a long time (ice thawing out)

RE: 1998 A/C air flow reduces to almost nothing
 

I had a similar problem with my '97. Turned out to be a VERY dirty coil. Pulled the blower out and cleaned ten years of dirt off the face of the coil, cured my problem.Fairly easy to do.
(Probably would have been a good place to put a filter.)
I also believe the dirt was holding the condensation and freezing.
David

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RE: 1998 A/C air flow reduces to almost nothing
 

All good ideas to check -- last thing to have checked is possible low refrigerant in system. That could possibly freeze up the evaporator coil.

Actually, low freon is quite easily checked. If the small (high pressure) line is hot and the large (low pressure line is cold), then the freon is not excessively low. If the low side is freezing, the freon can be low, but the high side may not be as hot. A guage from an auto parts place is relatively low-cost. Some "freeze-ups" on fairly late model computerized vehicles can also be sensors. Freezes can be caused by clogged a/c air filters or dirty coils resulting in insufficient air flow through the evaporator.