Tl;Dr at the bottom. Sorry for the wall of text.
Here's the situation. I got a call for a walk-in freezer that's been stuck running around 20°F for several days now. This is a new customer and our first time touching this unit. The in-house guy who has been here for years recently retired so they're looking for a new contractor. Great, let's do it!
I get there yesterday and go through the usual motions. It's an old Hobart box from the late 80s with it's original evap and condensing unit (compressor is 5 years old going off its serial number). Both evap fans are running. No ice build up on the coil. Condensing unit is located in top of the box. It's got a Copeland E body semi. Sight glass is still. Throw gauges on and check my pressures. Unit was R502 converted to R404A. Suction around 25-30psi, head pressure around 225-230psi. Ambient air going into the condenser measured at around 92°F. Suction seems a little high and head seems a little low for the current conditions, but nothing egregious. Let's continue.
As a precaution I blew nitrogen through the condenser and got a bunch of dust out until none remained. I also ran it through a defrost cycle to be absolutely sure the evap was clear of ice. Checked sight glass again and still full. Pressures didn't charge at all. Okay, doesn't look like it was a low charge being hidden by a plugged condenser. On to the next thing.
So because I have seen a few recently, and the same problems always seems to trend together (that and I wasn't ready to crawl off the top of this box to grab my temp meter yet either), I decided to do a pump down test. Verified that the liquid line solenoid works correctly, unit pumps down to about 8psi and cycles off and holds. After the I verified my receive valve holds properly because why not? Next I front-seated my suction service valve on the compressor and allowed it to pull into a vacuum. The compressor was able to pull down to 10" of vacuum (yes I purged the air from my low side hose). After 15 minutes it only rose up about to about 5". Looks like my compressor valves are holding.
Alright, time to grab the temp meter. I get myself set up on top of the box as there was none on the evap and I like to be close to where I'm getting my pressure readings from. That and the lineset was at best 5' in length (I feel like that's being generous). Connect my probe to the suction line and be sure to fully cover it in the 3/4" armaflex that's there. Check it after a little bit and I'm running a very high superheat of around 38°. After verifying a few things and double checking a few more, I ended up opening my TXV a full two turns (not all at once) my suction pressure came up 35psi, head pressure dropped down to about 220psi and my superheat down to ~30°. Box temp started to come down a little too (slowly). The box got as low as around 15°. My pressures or superheat never changed beyond that and the box just hovered around that temp. I did verify the TXV bulb was mounted and insulated properly. I also manipulated the bulb to see if the valve would open or close when wrapped around my hand or dunked in hot water. When the valve didn't respond, my boss and I decided to change out the TXV suspecting that the bulb may have lost its charge.
Fast forward to today. Come back to the site with a new valve (Sporlan FSE-1-ZP). Box temp is around 25° but the customer had been in and out of it all day. Pull the charge, installed it, changed the drier/sight glass, pressure tested, evacuated to <500 microns, held great on the drop test, charged it to to a full sight glass. Box starts to slowly pull down but lags at around 27° (wasn't helped by the fact that it had a revolving door today). I check my pressures and superheat. It's running 35/235 for pressure with around 30° SH. Make a couple adjustments to the valve and no change. The only difference is that my suction pressure was slowly adjusting with the box temp. Now I'm really starting to bash my head against the wall here because what the hell man.
Eventually I find myself back in the box only this time I notice something neither my boss or myself noticed yesterday. The evap fans aren't blowing out. They're pulling in. I examine it a little closer and discovered that the fans were turning CW with CCW fan blades installed. The motors are also reversible. I change the motors to CCW and I'm now getting blown in the face (like I could have sworn I was yesterday). I recheck everything when nothing really changed except my box was dropping slightly less slow. I should note that someone installed an Earthwize ECM fan motor controller with "Orange Motor" variable speed EC motors. The module seems to be defunct as it's receiving power but no LEDs are lit up.
I'm going back tomorrow morning to revisit some things. Obviously the box isn't working right still and I'm losing my mind. If anyone is wondering why I'm not staying until they job is fully complete each day, it's because the customer leaves by 2:30, and wants me gone by then. They're satisfied enough that is holding 15-20 to let it go overnight. A couple things I suspect at this point are that maybe with the fan controller not working, the fans default to max speed and it's moving too much air. Or perhaps there is in fact something wrong internally with the compressor and it's just not achieving enough compression. I'm truly stumped on this one and I'm swallowing my pride to post this here! Please help!
Tl;Dr High superheat and high suction pressure. Box won't get below 15°F. Sos send help.
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