McQuay PTAC mek009

[jare215th]

hello

i work in a hospital that has various different ptac, mostly mcquay MEK009 MEK012.
I'm having problems with the units after i replace the compressors, tecumseh RK124et and RK222et.

I believe i narrowed the problems down to the expansion valve cap tube strainer area. I believe i was installing the wrong fixed metering devices. Now i have the parker type 1/2 ton.
Constant Pressure Expansion Valves

Inlet Conn.: 1/4" ODF; Mfg. #: ASB20; Outlet Conn.: 3/8" ODF; R12/R134a Capacity: 1/4 to 1; R22 Capacity: 1/2 to 1-1/2; R502/R404A Capacity: 1/4 to 1;

Order # :B13-672Mfg. # :ASB20Brand :Parker Hannifin CorporationCatalog Page # :1132Shipping Weight :0.50Country of Origin :UNITED STATES Johnstone Supply

before i was removing the cap tube off the strainer and adding new fixed expansion valve, no info was provided for valve but pressures were 300psig on high side and 20f on low side. so i would charge by weight only 28.5oz r22. the units ran ok for awhile, but eventually would come back overheating and compressor burnt out or hard start

i guess my question is when using these fixed devices how important and or whats the reason for the bypass cap tube or secondary metering device often flowing backwards in the refridgation loop.

times are tough so i need to keep it cheap, so cap tub would be ok, but i'm very inexperienced with cap tubing, loops and what not.

i pretty much do best i can with as little info as i have to fix these mcquays, but i need some help, maybe some tips and tricks.

the chassis have a seperate heat coil, which are mostly dirty and i clean them when i replace the evap blower motor. when those go bad i'm installing 1250rpm dual shaft motor because are vent grilles are very narrow for safety reasons.

thanks for any info

[Starwarsith88HVAC]

I would put in new units and when they put new ones in tell them Amana is the best.

[ascj]

Have you talked to your McQuay rep(I'll assume no, due to Johnstone part numbers)........I thought they got rid of the AXV's and you just replace it with a single cap tube?

[jare215th]

hello,
i wrote this post so long ago i kinda forgot

anyway. no i havent talked to the mcquay rep. i asked my boss to, but you know how that goes.

what i did do is reattach the old cap tubing that would come off of the strainer then go into the fixed metering device, the parker type i had mentioned. it looks awful, but no leaks and runs well. when working on theses units i've learned that i need to be super clean and use a lot of nitrogen. they are soo small, no room for error.

the cap tube is a single tube, looped about 9x, and goes from a top the strainer and bypasses the parker valve, i assume to keep the pressure constant because the parker fixed type keeps the unit from freezing when freon is low and actually the cap tube does the cooling

i dunno, i love and hate these units. they are hard working son of guns (the one i'm working on hasnt ever been touched, 17years old!) but they are a pain to repair. i agree, we need new ones. but with all the cuts to mental health hospitals, AC units arent a big deal

thanks anyway