#3 is a combination of vacuum and electrical. This system uses the push button unit along with 12 volt/vacuum switchover valves. Additionally there is a temp control module mounted behind the glove box and the auxillary water pump which is mounted in the engine compartment. The switchover valves seem to be pretty bullet proof. The push button unit does have it's share of problems (solder joints) but can be rebuilt, the auxillary water pump can go bad resulting in burning out the push button unit (the aux water pump should be protected with an inline 2 amp fuse). The temp control module is fairly bullet proof. The vacuum pods under the dash which control the different vents can go bad (ruptured diaphrams) but can be replaced or repaired. Unfortunately, in order to repair/replace most of the vacuum pods the dash must be removed.

Any sort of vacuum leak can cause a malfunction in the climate control system.