Newbie - issues with refrigeration unit

[stealth987]

Hi Guys,

Its my first post here and I'm a bit of a noob when it comes to refrigeration, but I think you guys have the know how to point me in the right direction. I have a small refrigerated body fitted to my mazda BT-50 light truck and It was working fine up until last week when it started to struggle getting down to temperature. The unit is rated down to -18°C (-4°F) and I've noticed when my evaporator coil starts to get cold I notice now it only frosts up on one side, where it used to frost up all the way across. We are in the middle of winter and I can barely get -12°C, even on a long trip

Any ideas on what might be the problem? All the fans are working as per normal, and the compressor was recently replaced.

http://members.optusnet.com.au/jason.napper/IMG_20120523_154645.jpg

[stealth987]

Also during summer I could get -18 quite easily, so something is definitely wrong.

[vehikool]

Hi the very first thing a qualified person should do is fit a set of gauges and check are the gas pressures, suspect from looking at it that its low on refrigerant gas ( if you are not conversant with refigeration do not touch it, take it to a qualified person).
regards

[stealth987]

I did, they tightened up the compressor belt and put the guages on and the gas level seemed ok. They then ran the engine at 1500rpm for about 30 minutes to check, it seemed to pull down ok so they told me to take it away for a drive and see what happened. Assuming the gas levels are okay, the fans work and the compressor belt is tight, what should be the next diagnosis steps?

[moggy66]

It does lok like a low refrigerant fault, i would take it back and get them to recheck the pressures,check sight glass, and pull out the refrigerant to 100% check

Where abouts in Aussie are you?

[nike123]

Assuming the gas levels are okay, the fans work and the compressor belt is tight, what should be the next diagnosis steps?


Checking only pressures will not tell you much about state of charge.
Charge is checked by subcooling, if TXV is fitted.

What makes frost pattern like that in picture, is high superheat.
There are few reasons which could lead to high superheat. Therefore, skilled and properly qualified service engineer will take much more than only pressure readings.

Call someone else with better reputation.

[moggy66]

Transport units have there superheat set @ factory, so if to you your knowledge somebody has been messing around with it I agree with Nike123
but it shoud be set correctly.

[djbe]

Transport units have there superheat set @ factory, so if to you your knowledge somebody has been messing around with it I agree with Nike123
but it shoud be set correctly.

Thats always a problem, people not used to transport fiddling around with superheat.