Air-Conditioning Loss Is So Much Hot Air
Question: I have a 1981 Pontiac Gran Le Mans with a V-6 engine. I have two circumstances in which the air conditioning cuts out and seems to be replaced with heat. One is on steep hills. The other is when I stop and then go; as the automatic transmission hits second gear, the cooling is replaced by heat. It is driving me crazy. What is the problem?--H.E.B.
Answer: The air-conditioning system permits you to select settings that--in addition to regulating the air temperature--direct air to vents near the floor, on the dashboard or in the defroster.
A key element here is vacuum power from the engine.
When you change settings, the air direction is changed by a series of baffles underneath the dashboard that open and close with little vacuum-operated devices.
During acceleration the amount of vacuum in the engine drops quickly because the throttle plate in the carburetor opens wide.
What is probably happening is that the loss of engine vacuum causes the baffles to change position. The baffle that shuts off the flow of hot air suddenly opens. In some cars, the air flow shifts from a floor vent to a dashboard vent.
The problem could be caused by a failure in the vacuum reservoir, which is supposed to back up the engine by supplying vacuum temporarily.
Q: I have a 1984 Plymouth Reliant. At high speeds on extended trips, the voltage meter touches the red mark. It helps if I turn on the air conditioner and radio. In city driving, there is no problem. The original voltage regulator and two other regulators have been replaced, but the trouble persists. Is the problem in the voltage gauge?--M.M.
A: You are mistaking the dashboard gauge for a voltage meter. It is an amp gauge, which measures current and indicates whether the battery is charging. It does not say whether the charging system is producing adequate voltage.
The first thing you should do is have an electrical test conducted on your system. The voltage produced by the alternator should be in the range of 13.2 to 13.8 volts--definitely no higher than 14.5 volts. In addition, the charging system should be delivering only enough current to the battery to keep it fully charged.
Your description of the amp needle being in the red zone indicates the system is overcharging the battery. Overcharging will often result in acid being spewed around the top of the battery. So carefully inspect the battery.
