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Old 02-01-2010, 09:49 PM   #16
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HP - Compressor Failure 2x


The venstar does averaging too. I have my remote sensor for mine, I just havent made the time to install it yet.

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Old 02-01-2010, 10:35 PM   #17
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HP - Compressor Failure 2x


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The venstar does averaging too. I have my remote sensor for mine, I just havent made the time to install it yet.

Wow. Can't imagine why.
its not like you have anything else going on.
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Old 02-01-2010, 10:46 PM   #18
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HP - Compressor Failure 2x


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The venstar does averaging too.


Yes I know, I was quoting your link in my last post.
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Old 02-02-2010, 10:41 AM   #19
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HP - Compressor Failure 2x


The HVAC contractor came back out this morning.

Says the system is fine, the issue is not enough air-flow, which is causing the compressor to lock out and the e-heat to come on.

The contractor indicated too much flex pipe was used and that the maximum possible amount of airflow through the system (by adding up the pipe sizes) is under 1500 CFM.

So I ask, if a 5 Ton system with a variable speed AH is running at say 1000 CFM, will that cause the compressor to lock out?
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Old 02-02-2010, 11:41 AM   #20
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HP - Compressor Failure 2x


With low airflow the hot gas will not completly condense, or will do so slowly, this raises the pressure and the compressor will go out on high head pressure till the next cycle.
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Old 02-02-2010, 11:53 AM   #21
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HP - Compressor Failure 2x


Ok, he'll be doing the heat rise test tonight with and without the filter to see what the current CFM is through the system.

Once I know that number, I think it will assist in determining if there is a significant issue with Air flow or not and if I need to go over and make improvements.
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Old 02-02-2010, 02:07 PM   #22
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Are you going to be there when he does the test tonight.
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Old 02-03-2010, 09:53 AM   #23
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Originally Posted by beenthere View Post
Are you going to be there when he does the test tonight.
No, its about a 40 minute drive.

Return temp: 67
Supply Temp (w/filter): 94.5
Supply Temp (no/filter): 92.9
Heat Rise (w/filter): 29.7
Heat Rise (no/filter): 27.9

Amps: 84 @ 224
Watts: 18,816
BTU: 64,202

So 64,202/29.7 = 2,161 CFM

Did I miss something?
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Last edited by AndrewF; 02-03-2010 at 12:34 PM.
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Old 02-03-2010, 02:04 PM   #24
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HP - Compressor Failure 2x


Afraid so if thats from their unit.

How do you know how many watts the unit was drawing at the time the temp rise was taken.
Seen lots of guys "assume" that all the strip heaters were on, when only half were on. And then they think they have twice as much air flow as they do.

Takes around a 12X28/8X46 trunk line or bigger for a standard blower to move that much air through a single trunk line.

If the supplies are all 6" flex, it would take about 30 of them.
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Old 02-03-2010, 04:36 PM   #25
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HP - Compressor Failure 2x


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Afraid so if thats from their unit.

How do you know how many watts the unit was drawing at the time the temp rise was taken.
Seen lots of guys "assume" that all the strip heaters were on, when only half were on. And then they think they have twice as much air flow as they do.
He took the breaker panel off and checked it three different times.

He checked all 4 legs to the 60 amp breakers....one set of legs was 42 amps, the other set was 45 amps. So that is 87 amps, I took off 1 amp for the blower motor to get to 86 amps @240.
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Old 02-03-2010, 04:44 PM   #26
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HP - Compressor Failure 2x


They have very large duct work then.

Or several trunk lines.

PS: Since the blower motor makes heat from its electrical consumption. You don't need to allow for it. When its in the air flow stream.

A blower motor provides roughly 1250BTUs per 1,000 CFM of air flow.
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Old 02-03-2010, 04:47 PM   #27
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Taken his reading as accurate. And taken no more then 3' down stream in the trunk line. And taken at the air handlers intake. It would not be a lack of air flow that is causing the trouble.

Does this system have 2 trunk lines like yours? If so, did he check he rise in both trunks?
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Old 02-03-2010, 05:11 PM   #28
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Taken his reading as accurate. And taken no more then 3' down stream in the trunk line. And taken at the air handlers intake. It would not be a lack of air flow that is causing the trouble.

Does this system have 2 trunk lines like yours? If so, did he check he rise in both trunks?
His system is horizontal. From my recollection, he has a supply box that is the same dimension as the air handler and probably 3-4' long. There are multiple take offs from that box to the different areas of the house.

He called another contractor for a second opinion, they are coming out tomorrow.

We were not happy with the first contractors assessment, which included him only putting gauges on the system. HE added up the size of pipes and their rated CFM and said that was the problem...didnt even do a simple heat rise test, amp test, etc. He wanted to replace a lot of the ducting...I wonder if that is because he doesnt like flex ducting.
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Old 02-03-2010, 05:18 PM   #29
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Could be. There are hard core sheet metal guys.

Some of them have the motto "if it isn't sheet metal, it can't be right".

You should still check the static pressure.
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Old 02-03-2010, 07:01 PM   #30
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Could be. There are hard core sheet metal guys.

Some of them have the motto "if it isn't sheet metal, it can't be right".

You should still check the static pressure.
I understand sheetmetal (soild) ducts are better, less resistance, etc...but they are also harder to install in some situations.

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