my 97 silverado ac works for a short time then stops blowing thru the vents

[titus1.1]

The ac on my 97 chevy k1500 siverado works for about an hour then for no reason the air stops blowing thru the dash vents. The motor continues to run but will not blow thru the vents. At the same time my blower motor will slow down to the lower speed position even when I have it on high. But, if I shout off the ac for a view moments the air will start to come back up to speed and will begin to blow thru the dash vents again. I have replace all the blend doors excep the one for the cab recirculation. Replace the motor relay swith, the motor thermostat, and the dash mounted control module. Does anyone have any ideas on the possible solution? The heater system seems to work fine.

[Schurkey]

Where does the air blow from when it doesn't come out of the dash vents--the defroster outlets?

[titus1.1]

It does not seem to come out anywhere. It's as if all vent doors are closed. You can hear the blower turning at full speed but nothing is coming out.

[jdmccright]

Sounds like it is the blower motor itself or the blower motor resistor pack.

[titus1.1]

I just order a blower motor from rock auto. It should be here in a view days. I'll let you know if that is the problem. I have replaced the relay switch and the resistor pack .By resistor pack do you mean the one that goes inside the duct work with the multiple coiled wires ?

[jdmccright]

Yes, that is correct for the resistor pack description.

I should have mentioned checking all the connectors for oxidation as well. I'd had the same issues with my old Jimmy. Because of the amperage draw of the blower, I would find the surface of the connectors black with oxide, which increases the resistance, which causes the connections to heat up, which softens the housing plastic, which ultimately causes them to fail. You've already mentioned replacing most or all of the switches, but anything original still left should be checked for this.

[titus1.1]

Thanks, I'll be doing that and getting back to you

[2000CAYukon]

What happens if you change the temp to hot? I wonder if the evaporator is freezing up.

//2000CAYukon

[titus1.1]

I just had the entire a/c system replumbed last year when I discovered a leak on the high pressure side. They never mentioned any issues. I did clean a lot of leafs and debris out of the ducts in front of the evaporator. They did not replace my evaporator. If the blower doesn't do the trick I'll look closely at this item. How could you tell if it was frozen up? By checking the head pressure on the compressor?

[2000CAYukon]

Originally Posted by titus1.1

I just had the entire a/c system replumbed last year when I discovered a leak on the high pressure side. They never mentioned any issues. I did clean a lot of leafs and debris out of the ducts in front of the evaporator. They did not replace my evaporator. If the blower doesn't do the trick I'll look closely at this item. How could you tell if it was frozen up? By checking the head pressure on the compressor?

The hard lines going to the evaporator will probably be iced up as well. You should also make sure the compressor is cycling. If it is not cycling, it could lead to freezing.

//2000CAYukon

[titus1.1]

I'll be checking for this as soon as I install the blower motor.It should arrive today. I'll keep everyone posted