VCCA Home Forums TECHNICAL - GENERAL Tech Talk How do I test the wiper motor?

The wiper motor was disconnected when I received the car. I have the vacuum motor out of the car. It is mid winter and I have the care in 'hibernation' so just running a line from th engine to the motor is not an option. How can I verify that it works before putting it back in the car? If it does not work am I better off going electric?

You can use a vacuum line from any car as a source. I have done some limited testing with one of the Mighty-vac hand vacuum pumps. That will indicate if the motor might want to operate but it is really not a good test.

There are lots of posts about vacuum motors on these cars and how to revive them. I remember one article in the G&D about manually pulling ATF into one and letting it soak to revive the seals.

Converting to electric is an alternative but takes attention to details. I cannot remember if your car is converted to 12 volts. Mounting the motor, setting the pivots for the right travel, and connecting the arms all take some finesse. Plus you might need to modify other parts in the system to make things work correctly.

https://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html

WL

Venturi vacuum units like that work well with enough air compressor capacity. Otherwise the vacuum drops quite a bit after a minute or so.

I would be using the Craftsman 33 gal one I used to paint the car. I do not know what the exact specs are offhand but it was the biggest I could get that ran on 110 when I bought it.

Looks like this would let me bench test the wiper motor and get everything working prior to installing it.

It is to cold lately here to work much in the garage so I have been looking for small items that can be done in the basement or take a short amount of time in the garage.

Your compressor is a great vacuum source, you know, if you want to pipe it up.
WL

With that tank size you should be able to get decent vacuum for a couple of minutes.

I would try to figure out how to regulate the vacuum down to the 16 to 18 inches hg that an engine produces. That motor will work very well at 25+ inches hg but not necessarily so good at normal levels.

We’ll go a little off topic here.

The real capacity of a compressor is based on the size of the motor running it. At 110 volts the largest motor that could be on that unit is 2 hp. That size unit would have difficulty producing the required 4.2 cfm at 90 psi continuously.

Not quite right.
Compressor capacity depends upon pump displacement, RPM, AND/OR motor size.
Properly designed, the motor will be running at max power when the tank pressure reaches its high cutoff value.
A commercially built compressor will very likely reach this condition, maybe even overloading the motor during the last part of the fill, since for most of the cycle the motor is way underloaded.
Yes, 20A at 120V is 2.4HP, so your 2HO is right on.
Funny thing though, my 120V shop vacuum is rated at SIX HP!
For the motor test, one can either regulate the flow to the venturi (good) OR plumb in a valve between the venturi and the wiper motor.
The valve could be either in series with the vacuum line OR bleed the vacuum line to the atmosphere.
Regulating the flow from the compressor is best, because it minimizes air consumption.
WL

Can I just regulate it with the regulator on the air compressor? Or is it not the pressure that is the issue here?

Thanks for the compressor information, now I understand the ratings better on it. It is actually made by Devilbiss but labeled and sold by Sears as a Craftsman. The motor is supposed to run at 2HP 110v and requires a 20 amp circuit. I have it on a dedicated plug. It also can run at 6hp on 220v but I do not have 220v in my garage.

Hi Wilson,

Thanks for clarifying my statement. I should have said that the capacity of the compressor regardless of compressor size is limited by the motor horsepower. I agree that 2 hp is the about the limit on a 120v 20 amp circuit.

I did not think about trying to limit the vacuum through the pressure regulator. I am interested if that will work.

I would put a tee in the vacuum line to the motor and add a gauge so you can see what vacuum is being applied.

My guidance to control the vacuum is based on my experience with the wiper motor that came in my ”˜37. It would work fine with high engine vacuum and a wet windshield. If the vacuum dropped below 16” hg it would not work. I now have one that will work down to about 12” hg.

I have used the central vac in my house. It provides about 11” which is about what a vacuum pump on a fuel pump provides. I connect a hose from the wiper motor to a small funnel. I start the central vac, place the funnel opening on the pipe and it snaps in place from the force. Testing at the lower vacuum is a good challenge for the motor.