Alright, I need some suggestions based on the information below (it’s a long read – sorry)
Reason For Call:
Medium temp compressor short-cycling and all circuit temps +50F or warmer
Old Mom and Pop type grocery store with 1 compressor for all low temp and 1 for all medium temp.
MT (R401A) is a 6RA4-200A-TSK with 2 unloaders – #1 set at 20/12 and #2 set at 25/20. Suction control set at 12/2. There are 7 circuits on this compressor and all but 1 is controlled by t-stat/sol. (solenoids mounted in comp room). 24’ service meat is controlled by suction stop epr.
Outside ambient -9F. Roof condenser is a circuited – med/low temp. Header end fan set to run constant – 1st & 2nd stage controlled by ambient temp.
This is a new account and my first time on a call here. Log book in mechanical room indicated MT body had been changed 4 times in the last 7 years – the most recent being November of last year.
Repairs and Observations:
Receiver level 0%. Disconnected heat reclaim temporarily and opened disconnect on condenser. Added 40lbs R401A - pressures came up to 24/225 briefly and settled out at 20/125 after condenser disconnect was closed. I adjusted hold back to 110 psig and receiver leveled out at 15-20%.
Even at +50F the circuit loads weren’t sufficient to load up all 3 heads. Within 15 minutes run time, the compressor actually started to short cycle again as circuits were becoming satisfied.
I pulled info off circuits/compressor - came up with roughly 131,000 Btuh capacity/108,000 Btuh load.
At one point, there was only 1 circuit (4 door ZZ cooler) calling at 8,000 Btuh.
It doesn’t take a rocket scientist to figure out why the compressor is trashing itself every 1 ˝ years or so.
Possible solutions (or band-aids):
My first thought is to change the compressor to one that is suitable for the load but I just don’t feel right walking into a new account and telling them that $xx,xxx.xx is needed to fix the problem especially after they just spent God knows how much on repairing what they have.
Second thought is to change all t-stat/sol. to epr’s to help balance out the load. The compressor will still be over sized and return gas temp will higher than recommended but I’m thinking slow death by running with low load rather than fast death from short cycling.
Adding extra load doesn’t seem feasible.
More than anything, I'm trying to think of a cost effective means of extending the existing compressor life but I am open for ANY thoughts or suggestions on this one.