Strange 410A pressures

[beenthere]

This mobile home is a 16x80 single wide. The standard duct size on mobile homes is 4x12 from one end to another with the electric furnace sitting directly on top of the 4x12 trunk. Overall there is great airflow throughout the trailer.


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Great air flow? Or is it just blowing out hard? There is a difference.

[coolwhip]

1600 cfm through a 4X12 duct?…..like stuffing 10lbs. of crap in a 5lb. bag.

[buttwheat]

Existing line set is 3/4-3/8 which is undersized from the suggested 7\8 suction but have never run across this delima before and will only change it to 7/8 as a last resort.

So you only instal stuff properly as a last resort? Do you just wait until you have problems then redo it?

[superd77]

So you only instal stuff properly as a last resort? Do you just wait until you have problems then redo it?

The Line set is 10' long. Pressure drop shouldn't be an issue at that distance.


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[Jax]

If you will take the time to find the manufacture specs, you will know what the house is designed for. It is not just the duct size that determines this.
Northern Mobile do make it south. Most mobiles in our part of the world have a 4 x 16. 4Ts is a lot of air on a single wide.

[Saturatedpsi]

well I'll be darned my troubleshooting chart must be marked wrong its saying undersized suction line will cause low suction pressure must be wrong?

Yeah, but what does it show as the cause for low suction and low to normal superheat?

My troubleshooting chart has nine different reasons for possible low suction pressure another possibility might be restricted liquid line

And I've seen "charts" that gave 13 (count 'em, 13) causes for high head pressure...one being "prevailing winds". How many times you seen that?

A lot of the people who "make charts", have likely never been on a service call...they just think up possibilities that could lead to a particular symptom, without any consideration for other symptoms, that might or might not, accompany the first...

Without an understanding of the dynamics that provide the basis for a chart, troubleshooting, by way of a chart, is about like swapping parts...you eventually swap the one you couldn't diagnose, to begin with.

[ga-hvac-tech]

I agree it is probably low airflow.

Suggest to add some return and supply... or go back to 3 ton max.

[joedane]

not enough air flow and the system is oversized it will never work. not enough duct

[captaincompressor]

not enough air flow and the system is oversized it will never work. not enough duct

Put a smaller compressor in it with txv.

[ga-hvac-tech]

Went on a call (last call) Saturday... just after dinner... got home before dark for a change... LOL

First visit to the house... relative new system... about 3 years old... 50K furnace, 2 ton AC. Blower was a 4 sp motor, set on med-low.
SH was 30-something and SC was 20-something.

Put a clean filter in it (was not that dirty), and raised the fan to med-high.
Let it run for 10 minutes and the SH was down to mid 20's and the SC was down to mid teens.
Told the guy to let it run for a week or so... and we would check it again when in the neighborhood.

It saddens me to know folks do not take the time to set fan speed properly. Wish they would.

[oldguy1949]

This mobile home is a 16x80 single wide. The standard duct size on mobile homes is 4x12 from one end to another with the electric furnace sitting directly on top of the 4x12 trunk. Overall there is great airflow throughout the trailer.



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Did you put the blower upgrade assembly on or is it still a heating only blower?Better check as this is an older home it might have the factory low volume blower assembly,some guys are cheap on the original install.
Line sets are pretty short on single wides so 3/4 not a big part of this but makes for a quality install.
For the guys that don't live where it gets HOT ,4tons on a 16x80 on the cheaper build "homes with tail lights" is not uncommon .

[captaincompressor]

Put a 3/4 hp 1625 rpm on it...lol or cut out the bottom of the plenum and dump air under the trailer.

[superd77]

Thanks guys for all the help. I went back last night due to it being froze over. Upon arrival the unit was completely thawed(30 minutes).
Feeling that my SMAN-3 gauges may be off and not really wanting to lug them around i grabbed my standard gauges and clap thermometer.

Gauges up to find my SMAN-3's where WAY off. Gauges showed 275/115. It was 75 degrees outside. 78 inside. Sc was steady as a rock at 10 and SH fluctuated from 2-18 degrees.

I will be calling the manufacturer this morning about the blower size...it still has the "heating blower" in it.. 1/4 hp 1050 rpm now. I will be willing to bet it needs a 1/2 1625 or more. Hopefully this will resolve my issue.

Thanks again!


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[Jax]

Put a piston in and see what happen. May make it lots easier to see what is going on.

[oldguy1949]

It will be a 1/2 hp 1050 with a bigger wheel.The complete assembly isn't all that pricey.

[davoKC]

Yes. Let's hook up a 1/2hp motor to a straw. *sigh*

Why are manufactured home builders allowed to get away with such crap? EVERYTHING they produce is complete crap. unsafe garbage. Every other builder in the world has codes to worry about. Trailers can do whatever they want. Most inefficient home on the planet. And they feed their customers huge lines of crap. The most popular saying I hear from EVERY trailer owner is this:

"Oh you get what you pay for. This trailer is well built. I paid extra for the thicker insulation and better windows blah blah blah..."

The walls are 3" thick and the windows are single pane. Walking on the roof is like jumping on a trampoline.
Sir, your trailer wouldn't pass even the most basic building inspection. Period. The only thing that's rugged is the steel boat trailer it rode in on.

[jiffypop123]

Was this a replacement from a r22 unit? What size was the old unit and did you do a flush on the existing lines. We never reuse the lines from a R22 system on a new 410a system.