1999 Bonneville 3.8.
AC blows out of defrost vent.  Perhaps Vacuum Leak?  Defrost works correctly.  What you think?  I know
it has freon leak.. added last year and this year.
Yes, most likely your problem is a vacuum leak. When this happens, the system defaults to blow air
out the defroster as a safety feature. Check the large purple vacuum hose coming into and under
the passenger side of the dash from under the hood. The hose is connected to a vacuum reservoir
ball. It is usually located near one of the fenders. Follow that hose to look for a broken line.
1999 Pontiac Bonneville 3.8. A/C clutch will not engage.I recharged the system and weighed in the
new charge.

Fuses are OK, I tested the Clutch relay and it works on the bench. My book is telling me a
Powertrain Control Module grounds the Clutch but it doesn't tell me where it is and my diagnostic
tester (Actron CP9580) does NOT pull up A/C codes. The clutch on the compressor functions when
I cheat the circuit at the rely and it does get cold. Any Help?

This has been intermittent for a few months now and this past week it just threw in the towel. Clutch
will Not engage in any of the functions including Defrost.

Yes, the PCM grounds the clutch relay. It is located inside the air cleaner box. You would need a
schematic to check the proper wires to see if the PCM is actually grounding the relay. It does sound
like the computer is the problem though.

1995 Pontiac Bonneville. When I turn on the heater, it only blows out cool air. I can hear the air
pressure drop when I switch the temperature control from cold to hot. What could my problem be?

Hello and welcome. This sounds like the heater core is plugged up. With not enough coolant flowing
through the core, the air temperature won't get hot enough. This is as long as the temp door in the
dash is moving and the coolant level is full.
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Pontiac Bonneville A/C Clutch Won't Engage