How many CFM's Required to Pressure Test MH?

[Ductape_Dave]

I need to help out a friend who has a class C with a leak. For those that have performed the pressure test can you tell me what is a good CFM for a test blower to pressurize the unit?

Thanks in advance!
Dave

[Old-Biscuit]

HERE is a good article on DIY Leak Testing.

[j-d]

I've thought of building a pressure source with a jobsite ventilation blower. Mount it to a piece of plywood with a foam gasket to seal to ceiling around the 14*14" bathroom vent. Hold it in place with battery hold-down bolts.

Two blowers from Harbor Fright. I tried to size the pix to approximate the dimensions given on HF's specs:



The $79 yellow one is rated around 1500 CFM and the $49 red one is 300 CFM. Wish I could be sure that Red's capacity would be enough.

Also, Yellow could be easily mounted to the bottom side of the plywood adapter I'm thinking of. I'm sure Red has an intake on the opposite end that isn't pictured. It'd take some kind of ducting to provide air to both intakes.

From what Golden says, the Red blower might do it and the Yellow should...

A BIG Shop Vac might provide enough air in Blower Mode too. To me, it shares the Leaf Blower Limitation of how to connect it to the RV.

[oldbeek]

I used one of those big blowers from a rental yard that is used for drying out a carpet after a flood. Still didn't find the leak. The leak was the seal around the AC unit. You can not see the seal with AC installed.

[Golden_HVAC]

Probably a 250 CFM fan will work fine.

Normally you can remove a furnace fan, and if it is 120 volts (from your home furnace) you could use that, if you know anything about how to wire 1/2 of a extension cord to the fan motor leads.

Basically the white or yellow wire is normally connected to the white wire from the extension cord. Then the black wire is high speed, blue med, red low. Sometimes there are orange and yellow speed taps, usually there is a wiring diagram on the motor itself.

One person used a copy paper box, hooked up the blower motor to it, and then placed it over a open roof vent. It will blow 250+ CFM into the RV. Then spray the sides and roof with some soap that will foam up.

Dishwasher soap is designed to never cause soap bubbles, so don't use that. Also automatic washing machine soap is also designed to not foam up to much.

Other soaps, such as Dawn, or your favorite dish soap should foam up well. Check it with a fork in a small bowl, with a little water. Beat it like scrambled eggs, and see if it foams up. Then put some in a 1 quart sprayer (home depot, garden section where it is used as a chemical sprayer for about $8.) That will effectively coat the RV in a few minutes! Then open another roof vent, close the first one, and check the first one with soap, and the fan moved to the second vent.

If you run a furnace fan without a load on it, such as while in 'free air' the amp draw will be really high, and bad for the motor. Restrict air flow by not allowing it to free flow, such as making the output a higher pressure, and the amp draw will fall off, and motor speed will increase, and everything is fine. So while the cover is on the RV, this will restrict air flow enough to work fine, but if the box is uncovered, it must be shut off, as the motor without a load can blow to much air volume, and overheat it in a short time.

You will be leaking air through the air conditioning system outside (dash air) and other air leaks such as through your basement. So that is why I am recommending 250 CFM minimum. Most home furnaces will put out upwards of 800 CFM, and a 5 ton A/C equipped fan can put out 2,000 CFM at 1.2" water column pressure when on high fan speed (the black and white wires). By running on low speed, red and white wires (typically, check your wiring diagram and make sure it is rated at 120 volts, or that you are hooking it up to 220 volts) you should have at least 500 CFM if the fan is more than 8" wide and more than 8" in diameter.

Good luck with your project!

Fred.

[John_Wayne]

Had a friend do his with a leaf blower.