High low vacuum light on above 1000 rpm

[nels]

I started my 78 J model the other day and noticed the high/low vacuum light was on in the annunciator panel. When I idled it back to 1000 rpm the light went out. Revved it up a little and it came back on. The pump is new so I figure the filter might be restricted? Or a pinched vacuum line? I looked under there today and found the filter located at the center top of the firewall under the glare shield. I assume it is mounted on the regulator. The filter is the foam type and I assume it is a B3-5-1 type which I imagine is pretty much universal? I think if I take the foam filter off and start the engine I should be able to determine if the filter is the culprit or I need to look further. If the light stays out I just need a new filter.

Do those filters just slide on and off like a sock? Do I have to take off the glare shield to work on it? If so, are there any tricks to removing the glare shield .

Edited November 27, 2016 by nels

[Marcopolo]

Is the light on solid or is it flashing? Light on solid is too high a vacuum, flashing is too low.  I ask because you mention it is on at higher RPM and you have a new pump.  Regulator may need to be tweaked to accomodate the new pump.

 

The pre-filter (garter) does just slide over the main (canister) filter.

 

Ron

[nels]

Ron, thanks for that info on the light. It does stay on so it is, as I suspected, high vacuum.  The light didn't go on right after the pump install but maybe the veins had not seated/sealed yet?

Is the glare shield difficult to remove? I would think putting the garter filter on or adjustment of the regulator would be a lot easier with it off unless it's a pain to remove.

[nels]

Well, I put a new foam filter on the regulator and I still have the high vacuum signal showing on the annunciator panel. I guess the next step is to adjust the regulator? Again, I assume removing the glare shield is the best way to do this.

[Piloto]

Most likely it is the vacuum pressure switch. It is attached behind the gyro. There is a screw adjustment on its back side.

José

[nels]

1 hour ago, Piloto said:

Most likely it is the vacuum pressure switch. It is attached behind the gyro. There is a screw adjustment on its back side.

José

Thanks for the reply. I was starting to think I had stumped the panel. 

Do you think cold weather has an effect on this switch? Seems like I read somewhere that the switch can be dismantled and cleaned. Or is it just as well to adjust it? Also, I changed the girdle filter on the regulator with no change. The only other filter I could find was a tubular filter for the auto pilot. Isn't there usually a couple filters on the intake side of some gauges?

 

[Piloto]

42 minutes ago, nels said:

Thanks for the reply. I was starting to think I had stumped the panel. 

Do you think cold weather has an effect on this switch? Seems like I read somewhere that the switch can be dismantled and cleaned. Or is it just as well to adjust it? Also, I changed the girdle filter on the regulator with no change. The only other filter I could find was a tubular filter for the auto pilot. Isn't there usually a couple filters on the intake side of some gauges?

 

Pull the switch from the gyro. Under no vacuum it should light up the annunciator light. Apply vacuum by mouth and the annunciator light should go away. If not adjust the small screws on the back to get the desired results. In mine I found a vacuum leak due to the cartridge was not sealing well against the O ring inside the case. I put a little bit of silicone, readjusted and problem solved. There is no risk of damage by mouth vacuum. The most I could pull was 7"Hg.

José

[Guest]

The maintenance manual shows the procedure for adjusting the vacuum switch, there are two adjustments for high and low settings.  I use a vacuum pump and gauge, to set the values, I'lI leave the sucking to others.

Clarence