I have a 1999 Passat Wagon. The fuse (30 Amp) for the heater motor blew. I changed it, and it held for 2 days. The 3rd fuse lasted for only 20 minutes. What could the problem be???

To check! See if there is voltage at the fan connection at the fan with fan switch on.(with a test light ) If there is then it could be a bad motor. If no voltage check for blown fuse, or a bad fan resister. God-Bless! Often there are 2 separate circuit fuses one under the dash fuse block usually a 20 amp. There can also be a 30 amp Maxi fuse in the engine bay panel. Good-Day!

Fuse # 20 or 21 gets power through ignition. This fuse controls PRNDL indicator, speedometer, tach, & will cause transmission to not shift gears correctly. Ours took off in 3rd gear when put in Overdrive & only ran in 3rd gear. If we tried to manually shift thru gears (auto trans), it had 1st, 3rd, reverse. No 2nd or over drive. Replaced ignition. Fixed problem. Root problem was Electric motor that engaged 4 wheel low side was bad. Every time we used 4 Low side it threw power surge through ignition & blew ignition out. Good Luck.

you have a dirrect short .

Following wiring from the blower motor back to see if there is a short somewhere in that part of the harness, also check the relay.

Many cars have the cooling fan on a thermostat or time delay, to allow it to run for a short period of time after the engine turns off, to cool the engine off. You may have just never noticed it before. So I wouldn't worry about that.
Your real problem is the blowing fuses, apparently you have a short somewhere in your wiring. Putting in bigger and bigger fuses is a great way to set fire to your wiring harness. It's possible that the wire is pinched or chafed somewhere, and perhaps when you hit a bump just right, it touches and shorts.
You may have to take this to the Chevy dealer or a GOOD independent shop to have them chase it down. Unless someone out there knows exactly what this is, it could be a tough one to find.

Check fuse 27 15/20 amp located end of dash driver side
Open door remove plastic panel

did you tested climate control switch for power

fuse #18...yellow...20 amp

Try changing the fuel filter first we always change them when servicing the fuel pump anyway,its easy and cheap,if that doesnt solve the problem you will have to perform an amperage draw test on the fuel pump to insure your not replacing a good pump. Check the fuel pump relay and inertia switch and wiring also.Although possible its unlikley the fuel pump would blow a fuse consistantly without displaying any driveability problems.There may also be another component running off the fuel pump fuse have your mechanic pull a wiring diagram to find out. Good hunting keep me informed

Fuse #8, #18 and #22.

Below is a listing of which fuse corresponds with which circuit:

1 - 10 Amp - Transmission Controller, Gauges, Autostick
2 - 10 Amp - Right High Beam Headlight
3 - 10 Amp - Left High Beam Headlight
4 - 10 Amp - Radio, CD Player
5 - 10 Amp - Washer Motor
6 - 15 Amp - Power Outlet
7 - 20 Amp - Tail, License, Parking, Illumination Lights, Instrument Cluster
8 - 10 Amp - Airbag
9 - 10 Amp - Turn Signal Lights, Turn Signal/Hazard Indicator
10 - 15 Amp - Right Low Beam
11 - 20 Amp - High Beam Relay, High Beam Indicator, High Beam Switch
12 - 15 Amp - Left Low Beam Headlight
13 - 10 Amp - Fuel Pump Relay, Power Train Control Module
14 - 10 Amp - Cluster, Day/Night Mirror,Sunroof, Overhead Console, Garage Door Opener, Body Control Module
15 - 10 Amp - Daytime Running Light Module (Canada)
16 - 20 Amp - Fog Light Indicator
17 - 10 Amp - ABS Control, Back Up Lights, Daytime Running Lights, A/C Heater Control Cavity Fuse Circuits
18 - 20 Amp - Power Amplifier, Horn
19 - 15 Amp - Overhead Console, Garage Door Opener, Trunk, Overhead, Rear Reading, and Visor Vanity Lights, Trunk Release Solenoid, Power Mirrors, Power Door Locks, Body Control Module, Aspirator Motor
20 - 20 Amp - Brake Lights
21 - 10 Amp - Leak Detection Pump, Low Rad Relay, High Rad Relay, A/C Clutch Relay
22 - 10 Amp - Airbag
23 - 30 Amp - Blower Motor, ATC Power Module
24 - 20 Amp - Power Window Motors
25 - 20 Amp - Power Door Lock Motors, Power Seats