52* air at evaporator, 82* air at closest register


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Old 08-09-14, 12:44 PM
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52* air at evaporator, 82* air at closest register

So I already know I need new ducts in the attic and I need more insulation and better ventilation up there, but something else has to be going on for the air to get that hot. I put a thermometer right over the coil and the air is coming out at 52*. I put the thermometer into a register that is about 4ft of ducting away from the box and the air is coming out at 82*. If I pull the air filter out of the return air, the air from the register will cool down to 80*. The air temp at the return air is about 90* What in the world is going on? Is there something in my distribution box in the attic? I'm already looking into new ducting because I can feel some air leakage, but not in this particular duct and I'm also looking into an attic fan but it still should not be so high.

Thanks
 
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Old 08-09-14, 01:30 PM
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Does it have good air flow out of the register?
 
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Old 08-09-14, 01:43 PM
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It feels like it does, but I don't have any way to measure the actual CFM coming out.
 
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Old 08-09-14, 02:12 PM
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Is it a heat pump with electric heating elements, or does it have electric heating anyway, that may be coming on?

That's a 30F temp-rise within 4 feet.

What is the temp in the rooms?
Is the return pulling hot air from the attic?
 
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Old 08-09-14, 02:30 PM
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It is a R-22 central AC unit with gas heating. The system is in a closet in a hallway; the return pulls air from the hallway. The temp. in the rooms is about 90*. After running the AC for about an hour there was not any noticeable temp. difference.

I went into the attic and I didn't find any leaks up there.

The outside unit is about 10 years old and the inside unit is original from 1986. The coils have been cleaned but I don't think that's the problem since it's 55* there. I honestly cannot think of what could be causing a 30* rise in 4ft.
 
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Old 08-09-14, 06:31 PM
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Can you check the air temp at different spots of the coil ? Is there anything in that 4 ft of duct ?
 

Last edited by clocert; 08-09-14 at 08:37 PM.
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Old 08-09-14, 07:03 PM
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I agree with HVAC Retired. It sounds like you have an electric heat strip that is stuck on.
 
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Old 08-10-14, 03:52 AM
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Well, did U use an infrared thermometer? That would be a false reading of coil temp NOT air temp.
You should only use an air probe thermometer; preferably a digital that reads in tenths degrees.

Perhaps you took the temp too close to the evaporator so it sensed the coil temp & not the air temp.

With 90F return air temp, due to perhaps very high humidity it only had a 10 to 12F 'sensible' indoor temp-drop.

Try taking the plenum temp out of the line of sight of the coil with an air-probe TH & then see what air temp you get.

Also, take the temp-rise off the outdoor condenser; that will tell U how much latent Btuh it is removing from the indoor air.

Log outdoor temp + the condenser air discharge temp-rise. This will help with troubleshooting the system...also need the indoor %Relative Humidity reading...

With the above scenarios it could be possible to have a high 80F duct reading from a 90˜F Return Temp... Does it ever bring the room temp &/or humidity level down?
 
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Old 08-10-14, 04:26 PM
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I will try checking at different places on the coil. I don't think there is anything in the ducts but I'm not sure. There isn't any reason for anything to be in there.

I am using a analog probe thermometer. When I measured the air from the coil, I put the thermometer into a hole in the plenum where a refrigerant line comes out, taking care the thermometer did not touch the line. It was probably a few inches off of the evaporator.

I know for a fact there is not any electric heating in the system.

I will take the outdoor temps as well. I can feel warmer air coming from the condenser.

The AC will bring the temp. down in the evenings after it runs for a long time. It will not bring the temp down during the day. This is a recent development though. It used to cool just fine on hotter days.

Using a set of gauges the system is about 150 psi static and 225-230 psi high side and 25-30 psi on the low side.
 
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Old 08-10-14, 05:27 PM
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Your suction pressure is way low. Call a pro to check it out.
 
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Old 08-10-14, 05:33 PM
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What should the pressures be?
 
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Old 08-10-14, 05:38 PM
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The AC will bring the temp. down in the evenings after it runs for a long time. It will not bring the temp down during the day. This is a recent development though. It used to cool just fine on hotter days.

Using a set of gauges the system is about 150 psi static and 225-230 psi high side and 25-30 psi on the low side.
R-22: The low-side is way low at 30-psig; there are refrigerant system problems!
That, at least, explains part of the mere 10F temp-drop compared to the 90F room air temps.
The system is NOT cooling...
 
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Old 08-10-14, 05:48 PM
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Just to restate...discussions about charging and working on the sealed part of the system are a no no here. No issues with what's already been stated. Looks like a Pro needs to be called in to evaluate the overall system.
 
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Old 08-11-14, 10:48 AM
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Two years ago there was a leak in the system. We had a guy come out and fix the leak and refill the AC. I looked at the outside unit and the original fix looks oil free. There is a spot on the condenser coil that is darker than the rest and is looks like there might be some oily residue on the ground underneath that area. It's on the inside of the coils toward the bottom.

Every AC guy's answer that I've ever talked to is "oh yea, you need a new system" before they even make it up to the outside unit so I have a hard time trusting their opinion on if this one is fixable or if it would be cheaper in the long haul to get a new one.

Does anyone know of a trustworthy AC tech in the Cedar park, TX area? What would be a ballpark estimate for a middle of the road AC?

I'm decent with tools. Would it save anything for me to do the installation and then have the pro come out and connect everything and fill?
 
 

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