N9434V Posted February 3, 2021 Report Posted February 3, 2021 1970 m20c. Went to fly today to play with my new garmin gnc355. Three things amp meter not moving vacuum pressure was high and attitude indicator was a little slow spooling up. With the help of my a&up friend we looked for the cause of issue. 1. Amp gauge a. Amp gauge has about 2.3 ohms of resistance and does move with external source of voltage. b. Alternator and regulator are working confirmed with volt gauge plugged into cigarette lighter c. One wire to the gauge does indicate battery voltage. Other wire on gauge does not indicate voltage. . d. I still need to verify continuity on the second wire, I am Assuming it goes back to the regulator but have not yet consulted the wiring diagram in my manual Thoughts? 2. Vacuum gauge a. Hooked on my mighty vac and pulled 5in and gauge indicated same b visually inspected vacuum lines and all look good with no kinks Thought? 3. Attitude indicator Guessing cool morning and thick grease appreciate any thoughts, direction, other things to check Dennis Quote
carusoam Posted February 4, 2021 Report Posted February 4, 2021 Amp gauge... is a volt meter, measuring V drop across a calibrated resistor called the shunt... Find the two wires going to the shunt, check their fuses... Both wires will be reading about a nominal 12v... If one isn’t, check its fuse... PP thoughts only, not a mechanic... Best regards, -a- 1 Quote
carusoam Posted February 4, 2021 Report Posted February 4, 2021 High vacuum... that’s how our vac pumps work... they get modulated by a regulator... See why the vac regulator isn’t working as expected... Your POH probably has a drawing of the vac system showing where all the key parts are... Review that early on... PP thoughts only, not a mechanic... Best regards, -a- Quote
N9434V Posted February 4, 2021 Author Report Posted February 4, 2021 Thanks will give those a look Quote
tmo Posted February 4, 2021 Report Posted February 4, 2021 7 hours ago, carusoam said: Both wires will be reading about a nominal 12v... I always thought one of the wires will be +12V and the other one will go on to the electrical system - IOW, when disconnected from the amp meter, only one of the two wires will be live. Once connected, both terminals should show basically the same voltage, assuming no load, but the "from" wire itself will not be live. 1 Quote
N9434V Posted February 4, 2021 Author Report Posted February 4, 2021 Carusoam you nailed the ammeter. I found a wire broken on the end of the fuse holder. Problem solved it will be a couple of weeks before I can chase the high vacuum. Any recommendations on where and for what I should be looking. I really appreciate the assistance. Dennis 1 1 Quote
cctsurf Posted February 4, 2021 Report Posted February 4, 2021 2 hours ago, N9434V said: it will be a couple of weeks before I can chase the high vacuum. Any recommendations on where and for what I should be looking. I'd look for a clogged vacuum filter. Mine goes around the vacuum regulator, which (in my '62) is on the back side of the firewall (toward the passenger compartment). My vacuum was high and we replaced the filter and now it is much better. Just thinking about it, I'm curious about all of the filters on the back of the instruments... They've been there for years, I wonder how they are flowing... hmmm... might be worth a check. James Quote
Vance Harral Posted February 4, 2021 Report Posted February 4, 2021 One possibility on the vacuum regulator is that the tab or safety wire which is supposed to hold the adjusting nut in place has come loose, and the nut has spun all the way in/out/off/whatever to the "unregulated" position. Quote
jamesm Posted February 5, 2021 Report Posted February 5, 2021 I guess my first question on the vacuum system is .... Has something changed vacuum system configuration? Did something new get installed? in Vacuum system was there a reason to disconnect the vacuum lines ??? I am real real embarrassed to admit when I stall my first G5 ( and my second G5) that I would kept trying to route vacuum return lines/hook up thinking that the pneumatic lines should act line a electric circuit. After talking to a local instrument repair shop they straighten me out on how pneumatic circuit works. I have was having a similar problem with vacuum regulator, where I was thinking it was thinking it was the vacuum regulator but mine was on the low side. if I remember correctly it was vacuum line(s) connections that I kept trying to put a return in the pneumatic circuit to the pump causing the problem. Since then I have installed 2 G5's and removed my vacuum system and over period of time. So with the 2 Garmin G5's and Tankair 's electric step conversion on the market.. https://flightenhancements.com/index.html There should be plenty of pre-owned vacuum pump(s), regulator(s), vacuum step servo, vacuum wing leveler servo , and vacuum pitch servo for spares parts. In have a pre-owned/ one time owner/ used Tempest Vacuum pump and/or vacuum regulator, vacuum step servo, vacuum wing leveler servo , and vacuum pitch servo. Also have fairly newly overhauled Vacuum Attitude indicator (I think it was overhauled within the last 5 to 7 years) and DG though cage shaft has cut in it . The set screw head was stripped out. The DG still functions when removed. if you are interested. James '67C Quote
carusoam Posted February 5, 2021 Report Posted February 5, 2021 13 hours ago, N9434V said: Carusoam you nailed the ammeter. I found a wire broken on the end of the fuse holder. Problem solved it will be a couple of weeks before I can chase the high vacuum. Any recommendations on where and for what I should be looking. I really appreciate the assistance. Dennis Thanks for the feed back Dennis! I learned a lot around here over the years... MS is full up with good people. Best regards, -a- Quote
Dreamlifter Posted February 11, 2021 Report Posted February 11, 2021 Dennis, Could you post a panel pic of your GNC355? Do you have an autopilot to couple up with the magic? Thanks! Quote
Matt Ward Posted February 11, 2021 Report Posted February 11, 2021 Re: the high vacuum, is it consistent throughout flight or only on takeoff / high power settings? My high vac light will occasionally come on during the takeoff roll but turns off by the time I'm at cruise. I also have a gauge that shows it just barely out of the green so it's not something I worry about too much. Quote
N9434V Posted February 11, 2021 Author Report Posted February 11, 2021 I will post some pics of the gnc 355 when I get back to the plane Hopefully before the end of next week 1 Quote
N9434V Posted February 11, 2021 Author Report Posted February 11, 2021 The vacuum pressure was running at almost 6 with full power and was staying high when throttle was pulled back to 1700 rpm Quote
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