MiniMax NT Heater - No Ignition Sequence

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This time I used the heater hose, at the switch, connected to the blower. Same result.
 

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You are definitely not developing enough pressure to close the switch. I am guessing that the first reading you took was with the manonmeter attached directly to the port on the blower housing.If you are sure that the blower housing port is clear, I would check for dirt buildup across the cupped vanes of the blower wheel or a blockage to flow through the heat exchanger. You can inspect the heat exchanger with a telescoping inspection mirror and a flashlight from the underside or by removing the blower housing and using a flashlight from above the heat exchanger and an inspection mirror underneath the heat exchanger
 
Blew out tubing & blower housing port with compressed air. Blew out the veins on the top portion of the blower outside of the blower bousing, as well as the motor itself (the motor was hot). So if the was an obstruction, it's surely gone now. Still reading .12.
 
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The vanes on the blower wheel have a concave cup in the direction of rotation. If they are dirty and have a buildup across the cup essentially removing the cup or part of the cup they cannot usually be cleaned with compressed air. You would check for this builup visually, just as you would check for blockage of the heat exchanger visually. If the motor was hot, it may be due to a weak capacitor or a problem with the motor bearings. This would slow the rpm of the motor resulting in reduced air flow and excessive motor amp draw (causing the motor to overheat). I noticed that your meter will not read capacitor microfarads (uF) in order to check the actual capacitance of the capacitor against its rated capacitance. Half the battle of diagnosing a problem is having the proper test instruments to check the operating parameters of the parts involved. It also seems that your meter only has a single decimal point resolution, making it difficult to precisely check any fractional (less than 1.0 ) parameter such as a fractional motor amperage and useful in only very basic testing. If the blower is the source of the problem you would need to check both the capacitor microfarads (uF) and the motor amp draw accurately.
 
I can get my hands on a better meter. This was the free one you get at harbor freight. I'll grab it tonight and check uF. How do I check the amp draw?
 
If you remove the top of the unit you should be able to get to the fan assembly. It usually only has a couple screws mounting it. Pull the fan assembly and check the fan itself. I am willing to bet they are rusted off.

Dan
 
Lol. Is there a trick to getting the top of the unit off? I can't find any screws or tabs holding it in place.
-Never mind, I figured it out.
 
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That looks to be in real good shape. There should be a port that the vacuum hose hooks to that could be clogged as well. If you still cant get a good vacuum signal to the pressure switch make sure the connections for the small hose are tight and don't leak. It is possible that the motor is not running fast enough to generate the proper flow and will need to be replaced.
 
I'm not sure about the age. I've only had the house for a couple months, but I can look tonight to see if it's indicated anywhere. I tested the Capacitance rating on a capacitor last night, according to some YouTube tutorials, and it's possibly dead (operator error is also possible), so I ordered a new one. I also picked up a clamp-on multimeter today, so I'll be able to check the amp draw tonight. I peered down the hole when I removed the blower motor, and didn't see anything that looked like it didn't belong. Also blew out any residual rust/debris that was down there.

One thing I also noticed, was when I reassembled the exhaust grille at one point, I didn't install the scoop correctly, so it was sort of blocking the exit air flow. I figured that might impede the horsepower of the blower, but when installed it correctly and pieced it back together, I was still getting .14 on the manometer.

I read somewhere that if the doors/access panels are not all closed up, I won't get an accurate airflow reading, since it's not drawing the airflow that it's supposed to. Is that true? should I have everything closed up? I don't imagine putting it all back together would get me from .14 to .95. I currently have the main door/panel off, as well as the blower access panel. I put the top back on when tried firing it up again, but left the door and blower access panel off.
 
To check capacitance I usually shut off power to the unit/heater and remove wire(s) from one insulated post(s) on one side of the capacitor and read capacitance with meter across the two seperate sets of insulated posts on the capacitor. Reading should be within + or - 10% of the label uf rating. If your capacitor read 0uf it would definitely be bad and cause the motor to slow and show a high motor amp reading and move less air. A trick when checking a small amp reading ( 1.0A or less ) with a clamp on ammeter is to loop the wire several ( 5 or more ) times around the jaws of the ammeter. Count the number of times that the wire goes through the inside of the jaws and divide your reading by that number to get a more accurate reading. Having doors or access panels off should not effect your reading as your system is the sealed from the burner entrance to the blower exit except for the blower exit grill. It will make a difference on a gas furnace where removing the cover to access the fan/blower allows extra/excess atmospheric air to enter the fan/blower. As long as you only have the front panel and the top outside panel off you should have no problems with your readings. I am not sure what you mean by blower access panel, but I assume that you are talking about the top cover that allows you to see the blower when it is mounted in place.
 
Wooooohoooo we (you) did it!!
Thank you so much for all your help, and your patience while helping me pinpoint the issue.
I replaced the capacitor tonight, and it fired right up. I wasn't sure if I was testing the old one correctly, cause I wasn't getting a reading. Tested the new one the same way and got 4.9. Popped it in and there we go!
Crazy how much airflow there is now that it's spinning the right speed!

I can't tell you how much I appreciate your help.

Thanks again random stranger!
-Dave
 

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