Troubleshooting Central Vacuum Suction Issues - Old Nutone CV-400 Power Unit and Upgrade to Cana-Vac

It's been a while since my last post - life has been flying by at a rapid pace - and I'd like to post how I verified my central vac performance and resolved the suction issue.

30 year old house, central vacuum was installed at construction, and when we moved into the house about 6 years ago - one of the repairs I had to do was to repair broken or unglued central vac piping that was accessible in the basement. The other thing I did at that time was move the central vac to a corner of the basement utilty room to get it out of the way. Once I repaired the piping issues - the central vac cleaned up about a pound of sand and grit that was lining the bottom of the central vac piping - and the system was serviceable.

In the past year however, it was clear that the central vac wasn't performing well - it couldn't pick small pebbles off the floor, and it really wasn't dealing with the dog hair all that well. I did some internet research - looked at my options - and the first thing I decided to do was to baseline the suction performance before doing any repairs - so I would have some data to show whether my repairs did any good.

I rigged up a suction test using a plastic shop vac adapter, some duct tape, and a vacuum gauge that I had in the garage for tuning dual carburetor motorcycles:

Shop Vac Tool Adapter - Opening Covered in Duct Tape - Vacuum Hose to Vacuum Gauge

Vacuum Gauge Hooked up to the Central Vacuum Port

Vacuum Gauge - Reading approximately 35mm Hg
35mmHg converts to about 19 inches of water column suction. Comparing that to specifications of new vacuum cleaners - new machines are rated to pull up to 110 inches of water column - so my system was performing at about 20% of a new machine. No wonder it was struggling.

The next step was to remove the Central Vac from the installation - so that I could get the covers off and inspect it - and once I had the central vac removed - I installed my Shop Vac on the piping system to check to see if I could remove any debris from the vacuum lines and improve the suction at the test port.

Install Shop Vac on Central Vacuum Piping to Test Vacuum Lines
This worked quite well - the Shop Vac was able to triple the suction at the test port - and I got to about 60 inches of water column. I think I was able to clean some debris from the suction lines as well - I tested each port in the house - however I don't think that I had any fully clogged lines that would have accounted for the poor Central Vac performance. One thing about this test - the Shop Vac worked quite well as a power unit for the Central Vacuum piping - you could probably do this in a pinch without the installation of a proper Central Vacuum power unit.

Inspecting the Motors of the Central Vac Unit
Next step was to remove the top cover of the Nutone CV-400 power unit to check motor brushes and the air pathways. I powered up the unit with the top cover off (you have to take care - there is live 120V AC in this compartment of the central vac - to inspect the running of the brushes. One motor was giving quite large blue sparks at the brushes - which seemed to be an indication that the brushes were finished. I also removed the motors from the installation and found that one motor inlet was almost completely blocked by a piece of plastic that had worked it's way by the bag filter at some point - which certainly would have impacted performance.

I then started looking for motor parts - brushes - for these two Lamb motors. The only numbers marked on the motors were these green letters on the vacuum housing. And guess what - no motor nameplate, no motor part number, and no part numbers on the brushes. No way to identify which motors these were, no simple way to order the replacement brushes online to make a repair with the confidence I would get the right parts. 

Casting numbers for the metal vacuum housings - these are not motor part numbers
Not cool - not putting part numbers on these motors / brushes - certainly not a way to support sustainable development and the ability to repair your appliances instead of replacing them. At this point - my option would have been to take the unit to a repair shop that would be able to identify the motors and make the repairs. When I assessed the time and cost of doing that - I decided to replace the central vac with a completely new power unit. I did some research on suction and performance - there is a liability with running two motors in parallel as this central vacuum is configured - you get much better performance with a single larger motor with a vacuum impellor of larger diamater, so I decided to go with a new, single motor, tangential bypass power unit made by CanaVac.

New Central Vac Power Unit by Cana-Vac
Measuring the suction at my test port - I was up to close to 100 inches of water column - a five times improvement in suction - and the performance increase was substantial at the end of the hose. This has turned out to be a great performance upgrade - although - I was disappointed that I couldn't repair the original vacuum but I figured that even once repaired it still wouldn't have great performance - it would have been limited by the sub-par performance of the smaller parallel motors.

Sources and Links

I hope you found this post useful. Feel free to ask questions in the comments section below. I answer all questions.


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