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View Full Version : Anyone have experience with Marvair wall mount units?


tater
June 21st, 2006, 08:54 PM
My ignorance will show, please be kind.

My official occupation is TV broadcasting, which is heavily dependent on HVAC. I am responsible for 50 ton of Carrier plus a few smaller units. I grew weary dealing with contractors and decided to go to school and get certified. No offense intended, it is simply that what once took 3 days, I may can repair in one. I have a fair working knowledge of refrigeration. That means I know just enough to be dangerous.

Here is the problem. I have a Marvair, 1 ton, wall mount, R22 unit attached to a communications shelter. The unit is about 10 years old and worked fine for the first 5. At that time it needed a new compressor. The compressor is the Tecumseh rotary type. That compressor lasted about a year. There have been 6 additional compressors installed in the last 5 years. In addition, the cap tubes have been replaced. The unit also has an external fan control and low pressure shut off for low ambient operation.

I visited the site today and found the condenser fan stuck, easy fix with a little oil. The unit was still running a high head, 350+, and high suction, 100+. I cleaned both coils and pressures looked good until the water dried. I had found some serious installation problems with the last compressor and questioned the charge. The site was not mine at that time! I don't have any tech data on this unit yet. Having nothing to lose, some of the refrigerant was recovered to the point where the pressures looked better, 70/260. Now performance is very low. The first half of the evap the coil is cool. The second half is not. The compressor is happier but still very warm. Needless to say, superheat is quite high.

Back to this unit's many repairs: I know of only one repair where nitrogen was pushed during braising. Also the filter/drier in on the suction side as there is little room on the liquid side. I now know it should be on the liquid side and external if necessary. These are also reasons why I have decided to learn this profession. Alabama has very good technicians and the other kind. The contractor license is easy to get also.

What is wrong with my unit? I suspect the cap tubes are clogged again! I want to gut the cabinet and install a window unit. My partner thinks we can flush the system when the cap tubes are replaced. We will replace/relocate the filter/drier too. What will flush this system of the contamination from all the repairs.

jmac00
June 21st, 2006, 10:55 PM
well, so far it sounds like you have about $10,000 into a $4000 system.

scrap the hole mess and go get a Mitsubishi Mini-split system, lots of tech support and parts are fairly easy to get.

if your pushing 100 psi on the low side and 350+ psi on the high, it sounds like someone over charged the system.

Changing Cap tubes acn be a real challenge for an experianced welder, let some amature do it and your asking for trouble.

If any part of an evaporator is blocked it is easy to fine, just look for frost on the tubes ~~~ Thats your blockage.

as far as filters go, on either line is fine, They are directional, so make sure they are pointed in the right direction and if it's a heat pump make sure you have a "BI-FLOW" filter in the lines

Rich Jr.
June 21st, 2006, 10:59 PM
well, so far it sounds like you have about $10,000 into a $4000 system.

scrap the hole mess and go get a Mitsubishi Mini-split system, lots of tech support and parts are fairly easy to get.

if your pushing 100 psi on the low side and 350+ psi on the high, it sounds like someone over charged the system.

Changing Cap tubes acn be a real challenge for an experianced welder, let some amature do it and your asking for trouble.

If any part of an evaporator is blocked it is easy to fine, just look for frost on the tubes ~~~ Thats your blockage.

as far as filters go, on either line is fine, They are directional, so make sure they are pointed in the right direction and if it's a heat pump make sure you have a "BI-FLOW" filter in the lines

Yeah, what he said. Your unit has been so screwed up it ain't worth fixing anymore. FYI if the motor is stuck, oiling it really is not the right answer, it is a temporary fix at best and if you get 90 more days out of it you should buy a lotto ticket too.

tater
June 21st, 2006, 11:26 PM
Thanks J-Mac. I would love to scrap this junk. I can gut the evap section and have a nice shelf for a window unit. $250 with a warranty. Best of all, I can always go to Lowe's and get another in a few years and be back in business easily. OT, are you riding in my direction this summer?

Rich Jr. I oiled that motor 2 years ago when it was stuck. It has run 24/7 since. The site hasn't been my responsibility for the past year and I couldn't service it. I have a new motor but I didn't have a hacksaw for the long shaft. The last time I pulled the motor I came away bloody. If this junk stays in use hopefully it can wait until fall. The temp was 95 degrees today. The motor isn't the issue now. Thanks.

Pegleg Smith
June 22nd, 2006, 12:34 AM
tater,
I see a complete replacement in the near future. I would ise a mini-split system, just because they are the better equipment.

tater
June 22nd, 2006, 07:56 AM
tater,
I see a complete replacement in the near future. I would ise a mini-split system, just because they are the better equipment.

I didn't mention it before as it didn't seem relevent, but we have done just that. All of our sites, except this one, has a new Friedrich split system. This site's unit came damaged. The replacement is due in next week. The old system was to become the backup. This is the reason a window unit will work fine.

wolfdog
June 22nd, 2006, 11:20 AM
A rotary compressor is cooled by discharge gas. They WILL BE HOT to the touch. If you got the temp down to what you think is normal, it is undercharged.

Here is the web site. http://www.marvair.com/air.html

Breeze
June 22nd, 2006, 11:26 AM
I would go with window unit in your case and have a backup for when they break.

tater
June 22nd, 2006, 12:04 PM
A rotary compressor is cooled by discharge gas. They WILL BE HOT to the touch. If you got the temp down to what you think is normal, it is undercharged.

Here is the web site. http://www.marvair.com/air.html

How hot is hot? This one will boil spit! Thanks.

tater
June 22nd, 2006, 12:06 PM
I would go with window unit in your case and have a backup for when they break.

I expect the replacement condenser next week from Friedrich. The backup window unit seems the best for this. Thanks.

wolfdog
June 23rd, 2006, 12:13 AM
How hot is hot? This one will boil spit! Thanks.

The rotary -not the scroll- is cooled by the discharge gas. The shell will be as hot as the discharge line.

tater
June 23rd, 2006, 11:39 PM
Had I known then what I know now! I called Marvair today. They referred me to a distributor. Some of the higher repair bills would have bought a new unit. The worst is that I never got kissed.

wolfdog
June 24th, 2006, 12:25 AM
I have worked on some Bard units. About the same thing. Like working on a window unit...hanging on the side of a construction office.

tater
June 24th, 2006, 06:03 PM
I have worked on some Bard units. About the same thing. Like working on a window unit...hanging on the side of a construction office.

We have Bards hanging on our satellite shelters. The attraction back to Marvair is that the holes will match. The order should be placed on Monday. Thanks.

pintofstout
July 7th, 2006, 09:54 PM
No flames on this one? forgot how much I like this site....

Those Marvairs can be odd creatures, I work on a ton of em. It seems pretty critical that their superheat be dialed in based on outdoor amb and indoor wetbulb, they fluctuate drastically. They run an oversized evap with a 25 degree indoor split, generally. head usually sits 40 over ambient on an average day, clean coil

I've seen em chew up compressers year after year like this one. While I'd bet the other one was way overcharged, does it have fresh contactors, cch, and does the enthalpy control work? Hows the amperage, mice chew on those wires and can throw em way outta whack.

Those things are made to be able to run super cold temps but they'll still wash bearings in the winter if that enthalpy control fails into mech. cooling mode. I'd check that too.

tater
July 8th, 2006, 07:30 PM
No flames on this one? forgot how much I like this site....

Those Marvairs can be odd creatures, ....... and does the enthalpy control work? .......Those things are made to be able to run super cold temps but they'll still wash bearings in the winter if that enthalpy control fails into mech. cooling mode. I'd check that too.

Please forgive my ignorance. Just a beginner here but doing better than some of the contracotrs I have used.

So far as the enthalpy control goes, we may have a terminology gap. The only control this unit had was a fan control switch. That was an early suspect and replaced with an adjustable control.

The last time I played with this unit some of the refergant was recovered to get the head pressure to a usable range. It just didn't like 350+ for some reason. After that I only had partial cooling. Two days later it had died again. I suspect blockage. I also feel the system is contaminated.

A new mini split Friedrich has been installed. A new Marvair unit has been ordered. Thanks.

pintofstout
July 10th, 2006, 12:20 AM
well I'm not sure where your from. I'm in Pittsburgh and our marv's run all winter long, they've got a pretty good load inside. our's are the compac 2's, they have an economizer built in so when the enthalpy gets low enough outside, they'll pull outside air.

If it's got an economizer, at the bottom of the midle compartment is a black box, which is the actuator, with linkage that operates the outside air damper. The Compac 1, I think, is not designed for low ambient operation and may not have an economizer. basicly, The compac 2 will open to outside air when It can mantain 55 (roughly) supply without having to run the compressor.

If it fails, the ambient can drop to 20 degrees and still call for cooling in the room. the compressor shouldnt be running that cold, but it will in the absence of a control. Their usually scroll compressor's, which are made to take some slugging cause the head lifts, but realisticly their bearings wash and they die. This means they can look great during a PM but be smoked by next summer.

Thats just one possible scenerio though, and given your initial presssures it probably got overcharged time and time again by someone hunting for a 40 degree evap temp or something. Like I said those babies are picky, contactors and chewed wires will toast em just as easy.

I manage the wireless communications side of my company and deal quite a bit with Bards and Marvs. Any help I can give ya, tech support numbers or common behavior problems, lemme know I'm happy to help.

Brian
brianautumn@comcast.net

tater
July 10th, 2006, 08:11 AM
well I'm not sure where your from.

Brian,
I am in Alabama. We have the Compac I models. We rarely see the ultracold temps. We have small heat loads so ours doesn't run when the temp is below 50 or so.

Have you found any of your units with a gap between the inlet and outlet vents? We found several with this open space. Air could flow from the evap coil through the fan and back to the evap coil. Tape fixed the problem. I may have a photo at work. I'll post it if I do.

tater
July 10th, 2006, 12:21 PM
Brian,
Here is the photo. The problem was an installation issue. We found several units that were never sealed to prevent bypass.

http://home.alltel.net/hyatts1/RohnACBypass.jpg

pintofstout
July 10th, 2006, 07:41 PM
Actually, I have seen that, on some shelters that come from Georga I think...That along with lead lag controllers that arent wired in right. They take a real thorough PM on startup.

the Bards are way worse than the Marvairs though when it comes to gaps like that, along the right hand side where the refrig lines to to the evap. You could put a fist through em to start, but once someone puts a drier on that liquid line, it's enough to really throw in outta whack, since they run such low evap pressures.

Just wondering, you guys have problems with mice out there?

tater
July 10th, 2006, 08:16 PM
Actually, I have seen that, on some shelters that come from Georga I think...That along with lead lag controllers that arent wired in right. They take a real thorough PM on startup.

the Bards are way worse than the Marvairs though when it comes to gaps like that, along the right hand side where the refrig lines to to the evap. You could put a fist through em to start, but once someone puts a drier on that liquid line, it's enough to really throw in outta whack, since they run such low evap pressures.

Just wondering, you guys have problems with mice out there?

Our shelters were built in Bessemer, Alabama. I don't know of any that were built in Georgia but could be. I guess the Bards need checking for gaps.

We have mice but I am not aware of any damage to our units.