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View Full Version : Air Pressure from Vents Hign then Low then High


dgsonic
Sep 6, 2008, 02:18 PM
For what ever reason my air condition unit just started to push air through the vents high then low then high after I turn off the unit for 5-10 minutes. When I put my hand to the vent it will be blasting cool air out for about 1 hour. Then it gets so low u can barely feel anything but the vents are chilly. If I turn it off for 5-10 minutes it starts blasting cool air for another hour then same thing happens. The air conditioning FAN is spinning with no problem, the furnace in the garage is spinning with no problem. I had a air conditoning contracteor look at it and said he was 90% sure it was Thermostat malfunctioning. He wanted to charge me $265 to replace, I declined and replace myself for $35.

I noticed that the air duct on top of the furnace in the garage was leaking water, which should be going through the PCV Drain pipe connected on top. But this other hole was sprinkling water out of it. The contractor said that hole should have been plugged so he put some putty on that hole, but now I'm having my doubts because that hole has been that way for 12 years with no problem. I think water now coming out of that hole only because the drainage hole is clogged.

My question is this... Is it possible the drainage line is getting clogged and that's why when I turn it off for 5-10 minutes the water is slowly running out enough for the unit to build up more pressure. Is it just a matter of cutting the PCV pipe and cleaning it to test to see what happens. Give me your thoughts.

hvac1000
Sep 6, 2008, 04:19 PM
Is it possible the drainage line is getting clogged

Yes

and thats why when I turn it off for 5-10 minutes the water is slowly running out enough for the unit to build up more pressure

Not unless the caged blower wheel is under water and I do not believe that is the case.

Clean out that drain and see how it works.

dgsonic
Sep 7, 2008, 08:50 AM
Well I didn't clean out the drain, I did something better to test before I attempted to lean drain. I cut the PCV Pipe coming out of the air unit going into the drain and just allowed the condensation from the unit to pour into my shop vac. When the Air unit is running well the water is trickling out of the AC into the Shop Vac with air pressure blowing. Then about 25 minutes later there is no more water trickling from AC and just small air pressure blowing out down into the Shop Vac via the hose. Then about 45 minutes later no water or air blowing from AC unit in garage. The outside FAN is still spinning and the blower in the garage furnace is still spinning.

My question is this... should water be continuous from the AC when its on? Or is that normal operation for the water to start coming out when first turning on then to stop. Also why after waiting 5-10 minutes it starts blowing normal again for 45 minutes. I have figured out that if I set it at a temperature that will make it shut off and come back on it will continue to work longer. But if I try to get it to drop the house temperature 6 degrees or longer the unit stays on to long and then it stops blowing tru the vents.

Any suggestions...

hvac1000
Sep 7, 2008, 09:04 AM
should water be continuous from the AC when its on?

Yes for the most part. There will be a lag during the start up for a minute or two and the same on shut down.

Your unit is acting like there is some kind of control is telling the unit to run the blower motor slower during startup and after a temp or time element is hit it speeds up to normal.

The other thought is that the capacitor for the motor might be going bad or the blower motor itself. I would replace the capacitor with like same and try that. It is a very cheap cure if it works. The capacitor for the inside unit is usually located near the blower motor and can be easily replaced. Turn power off first.

NEXT and important question before you try and replace the capacitor.
Brand and model number of the inside unit.
How old is this unit?

The reason for this question is that some of the newer units do allow variable control of the blower and I do not want you to get into that system. The motor is very different from a standard unit and it is NOT user serviceable. It is a DC voltage motor and with the end bell electronics can cost an easy 1000.00 or more. I should be back on later today.

dgsonic
Sep 7, 2008, 11:51 AM
The blower motor is turning full speed when the AC Contractor first checked it out. The FAN outside was spinning and the blower was churning full blast when he took the cover off. I had another gentlemen on another site say this sounds definitely like an Evaporator Coil could be freezing up with ICE and preventing air flow. He thinks since its never been "charged" that I might need it servicing for charge. The Payne Unit is 12 years old.

hvac1000
Sep 7, 2008, 12:14 PM
There could be dirt on the air in side of the coil causing it to freeze up and then thaw. Usually it will not thaw unless the outside unit is not running.

It could be low on refrigerant BUT it is a sealed system so there is never a need to charge unless you have a leak somewhere.

It is nice to know the age and model numbers since that can change the advice given on a unit. There have been many changes over the years that can lead to different answers for the same problem.

Good luck.

dgsonic
Sep 7, 2008, 12:22 PM
The furnace on the bottom is a Payne Model GB1AAV Upflow. I'm assuming the unit on top of that is called the "Evaporaor Unit" which has the 2 drain holes.. One has the PCV Pipes coming out and the other has an open hole. The Thawing makes since. Maybe that explains the water running out as soon as I turn the unit back on. The Payne unit came with the house which is 12 years old. Never had any problems with AIr or Heating in the 12 years. The air filter is brand new in the unit. The Blower in Furnace and Air Conditioning unit are running fine. None of the error codes are blinking per manual on the Furnace unit underneather the unit on top.