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Need Advice on Vacuum Pressure

Mr. D on Fri January 11, 2008 11:06 AM User is offline

I came across a Robinair 15600 (6CFM) vacuum pump for free, I changed the oil and tested it out last night with my TIF 4-way manifold gauge set. The best reading I got was around 19 In Hg vacuum and when I went to the isolation mode on the pump the gage went to zero.

So today I checked all my connections, cleaned all the fittings and hooked everything back up. This time however I used a digital pressure test set (very high dollar and very acurate) to measure the pump and compare the manifold gauge reading. The results were as follows:

Absolute Pressure: 14.738 psi

Vacuum Pump: 21.928 In HG

Based on the AP of 14.738 I should be able to pull vacuum down to 30.008 In Hg as per the "digital pressure test set" conversion selection.

So, I have a pump that will only pull 21.928 In Hg when directly hooked up to the manifold gauges and I'm sure will be lower when hooked up to the car AC system. Will this be enough to evacuate a system or should I look for another vacuum pump?

I have a lot of money tied up in restoring this 65 Corvette Factory AC system and want to make sure I get it right the first time. If it matters I have converted it over to a POA valve system and wil be using R-134a.


Dougflas on Fri January 11, 2008 12:42 PM User is offline

you need a better vacuum. Since the pump was free, send it into a repair center and get the Robinair repaired. It is a decent pump.

Mr. D on Mon January 14, 2008 2:42 PM User is offline

I called around about getting the Vacuum pump repaired and base on being able to buy a new Robinair 15600 pump for $249.99 w/ free shipping it was not worth repairing. The Vacuum Module cost $178.00 plus shipping so I wound be at least $200 into a repair.

So being the gearhead that I am, I took the pump apart to see what made it tick. Really a very simple setup with few moving parts, it has two carbon brushes in each stage that can go bad and they are removeable and the same on both sides. I just pulled them out of their holder, turned them around and put them back in.

Put everything back together and what do you know: pulled vacuum to 30.001 In Hg.

Dougflas on Mon January 14, 2008 4:27 PM User is offline

Great!! Good thing to know as this is a popular pump.

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