non ford AC question.
Thread Starter
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i ain't rite
Joined: Mar 2005
Posts: 65,446
Likes: 5,517
From: Marlboro Mental Hospital.
non ford AC question.
in work we have a kenworth T-800.
the evaporator freezes up after about 1/2 hour of running, and you have to turn the heater on for around 5 minutes to defrost it. then it works for another 1/2 hour or so before the cycle starts over again.
anyone have an idea as to what the problem may be??
the evaporator freezes up after about 1/2 hour of running, and you have to turn the heater on for around 5 minutes to defrost it. then it works for another 1/2 hour or so before the cycle starts over again.
anyone have an idea as to what the problem may be??
Fleet Mechanic
Joined: Feb 2006
Posts: 1,776
Likes: 5
From: Lorain County, Ohio
Do you know what controls the compressor clutch?
Does it use an Expansion Valve and a thermostat, or an orifice tube and cycling switch?
Most trucks that I've worked on use a TXV and thermostat, so I'll assume...
The thermostat senses the evaporator temp and turns off the compressor to prevent icing. It usually has a sensing bulb that attaches somehow to the evaporator. Some are inserted into the fins, some are clamped to the outlet pipe.
The 'stat may be stuck closed or the sensing bulb may be damaged or disconnected from it's mount.
A slightly low refrigerant charge can cause evaporator icing, too. I've heard about this many times but never actually seen it for myself. Take that for what it may be worth.
If the system uses a cycling switch, the switch may have shifted out of range or failed closed. It should open when the low side pressure gets down to about 26-28psi. That equated to about 33 degres evaporator temperature. If the pressure drops lower, the evaporator can get too cold and freeze.
Hope this helps.
Does it use an Expansion Valve and a thermostat, or an orifice tube and cycling switch?
Most trucks that I've worked on use a TXV and thermostat, so I'll assume...
The thermostat senses the evaporator temp and turns off the compressor to prevent icing. It usually has a sensing bulb that attaches somehow to the evaporator. Some are inserted into the fins, some are clamped to the outlet pipe.
The 'stat may be stuck closed or the sensing bulb may be damaged or disconnected from it's mount.
A slightly low refrigerant charge can cause evaporator icing, too. I've heard about this many times but never actually seen it for myself. Take that for what it may be worth.
If the system uses a cycling switch, the switch may have shifted out of range or failed closed. It should open when the low side pressure gets down to about 26-28psi. That equated to about 33 degres evaporator temperature. If the pressure drops lower, the evaporator can get too cold and freeze.
Hope this helps.
