3 June 2006

For several months now our AC/Heater control "door" switch does not change "door" positions when switched with control knob on our '97 AWD Astro (85K miles, bought new in '97).

"Detent" positions of control knob are felt as normal. The "door" always stays in "defrost" mode (i.e. air blows only from defroster no mater which "door" position is chosen with control knob).

Also AC compressor clutch does not engage when one of control knob positions for A/C is chosen.

Fan works normally at all speeds except in MAX position which should run blower fan at very high speed but runs instead at only "HI" position speed (i.e. with control knob in one of A/C modes).

I have checked all relevant fuses (inside vehicle: #'s 12 & 14 and under hood fuse box "A/C comp", "IGN-E", 30 amp "AC" and "RR HTR//AC" fuses) with visual inspection and ohmmeter. All are good. There are two relays labeled "A/C relay" and "AC enable relay" which appear OK with ohmmeter reading checking "pin to pin" resistance based on schematic printed on each relay, but I do not know how to test their function to be sure they are OK.

I would be grateful for any ideas on how to find and fix the problem now that summer is here in Utah!

Thank you.

Sincerely,
Robert H. Todd

Make sure the vacuum source/supply to the dash control is actually providing vacuum. There is a small vacuum line from the left side of the engine, through a check valve, to a "T" fitting where is splits to the HVAC control on the dash and to a spherical vacuum reservoir mounted along the right subframe rail. The vacuum reservoir can crack, split, the hose can break loose, or any of the other tubing or fittings in the line can fail. The hard plastic (nylon) vacuum line from the left side of the intake across the engine is particularly susceptible to failure due to the heat and close quarters. Any loss of vacuum will force the dampers ot the default mode - Defrost.

The blower problem is likely a separate issue. The lower speeds are powered directly by the dash-mounted switch, while the high speed is powered through a High Blower relay. Depending upon the model year, this relay may be mounted along the lower edge of the hood/cowl or in the underhood electrical center (fuse/relay panel).

The failure of the A/C clutch in one of the A/C positions may be a switch or wiring problem.

I'm having the same problem. I took the vacuum hose off where it goes into the firewall and there seemed to be a small vacuum while the engine was running. How much vacuum is there supposed to be...there was not even enough to leave a spot on my finger.

It seems there are 3 actuators on my 02 Astro. 1 controls the inside/outside air vent for max or normal ac. The other seems to control defrost and floor and the final one seems to close off the defrost/floor with another door that directs the air flow to the vents. All of that to say...earlier today the first two seemed to be working. Ie. it was changing from outside to inside air when switching from norm to max even though the vents weren't working. And you could switch between defrost and floor and the 2nd actuator would work.

Now that I've pulled the hose from the connection through the firewall (and put it back) and have checked all around the vacuum resevoir, nothing works. None of the actuators budge when I move the control knob.

Finally, I've noticed over the last month that as I accelerated my vents would stop working and air would go to the defrost...does this mean that the problem is in the resevoir...and if it is, how do you get to the stinking thing to work on it?

Thanks for any help you can give
Treefrog