N9405V Posted February 13, 2018 Report Posted February 13, 2018 Riddle me this, what could cause a low vacuum light at takeoff and cruise power, but not at low rpm or during the run up? I don’t have a gauge, just an idiot light on my 1970 M20E. The wing leveler/autopilot and artificial horizon work fine. Sent from my iPhone using Tapatalk
Mooneymite Posted February 13, 2018 Report Posted February 13, 2018 That High/Low vac switch can be twitchy....most seem to be installed to float somewhere on the vacuum line. Perhaps it is a vibration issue. See if you can borrow a vacuum gauge to install to check the actual vacuum pressure before you spend a lot of time/effort looking for a vacuum problem. 2
larryb Posted February 13, 2018 Report Posted February 13, 2018 I had the vacuum switch go bad on me. Fortunately my avionics guy had one lying around from his own Mooney, removed when the vacuum system was removed. I now also have a spare one, which was removed from my K this past summer. I’ll sell it if you need it.
Jim Peace Posted February 14, 2018 Report Posted February 14, 2018 Just had my vacuum system and standby vac removed......two G5's being installed...... So much more access behind the engine now.....
takair Posted February 14, 2018 Report Posted February 14, 2018 9 hours ago, N9405V said: Riddle me this, what could cause a low vacuum light at takeoff and cruise power, but not at low rpm or during the run up? I don’t have a gauge, just an idiot light on my 1970 M20E. The wing leveler/autopilot and artificial horizon work fine. Sent from my iPhone using Tapatalk Do you have a single light vs two lights? Is it possible that it is acting as the low and High vacuum light and it is responding to high vacuum? 2
N9405V Posted February 14, 2018 Author Report Posted February 14, 2018 I have the two light setup. Sent from my iPhone using Tapatalk
carusoam Posted February 17, 2018 Report Posted February 17, 2018 Previous owner installed a vac gauge on my O... The idiot lights just don’t give enough information. You don’t need to be an engineer to appreciate the added data... Looks like a mechanic may need to install a temporary gauge or a real gauge to get you to the next step... Do you have a JPI already? PP Thinking out loud, not a mechanic... Best regards, -a-
takair Posted February 17, 2018 Report Posted February 17, 2018 On 2/14/2018 at 8:32 AM, N9405V said: I have the two light setup. Sent from my iPhone using Tapatalk Does the low light come on when the engine is not running? 1
N9405V Posted February 18, 2018 Author Report Posted February 18, 2018 Does the low light come on when the engine is not running? Yes, and at low idle. Above 900 rpms to 1800 rpms light goes out. Then, when I apply take off power, it comes on.Sent from my iPhone using Tapatalk
takair Posted February 18, 2018 Report Posted February 18, 2018 Really strange. Would be best to insert a gauge to see what’s going on. Could be a bad switch or electrical. Maybe it responds to vibration vs pressure.
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