|
| If the high & low pressures are actually correct for the ambient temperature, then the ac has to actually be working. The pressures can't lie. The service manual has a chart showing what the pressures should be compared to the ambient temperature. If the pressures are right, then the ac sealed system is right. But you can lose that cold air in lots of different ways.
1) you say the heater valve was shot and was replaced. Do you mean the heater control valve beneath the seat, or the heater valve at the engine block? I wouldn't trust the one under the seat further than I can throw it. If you don't have block valves, you can buy an inline 5/8" valve at any auto parts store. Be sure you've shut off the coolant flow from the engine to the cab heater. 2) Scott mentioned the evaporator core being dirty, and it appears that the core was replaced on your tractor. So we assume there's no air flow blockage thru the evap core. Make sure the ducting beneath the cab didn't get knocked loose, and most of your nice cold air is being blowed back out to cool the rest of Montana down. 3) the radiator fan drive clutch can slip too much, and quit pulling air thru the condenser. This may not show up until the fan has operated for an hour or so, and your tech will have to check this under field conditions; not just watching the gauges on a stationary tractor. The high-side pressure will go up when / if the fan quits pulling sufficient air flow thru the condenser. 4) as previously mentioned, the ATC electrical on these tractors was not the best in the world. A bad return air temp sensor, failed ATC module, or corroded wiring connector in the HVAC module, etc shut off the compressor clutch engagement too soon. CNH has a 17-page service bulletin that describes in detail how to test every component on that system.
Are you seeing any ATC faults flash in the temperature display window?
Suggest that you make sure the coolant flow to the cab is Completely Shut Off. Even a small amount of flow thru the heater core will overcome a properly working a/c system.
If the flow is shut off for sure, you can bypass the HVAC electrical by disconnecting the clutch wire at the compressor single-wire connector and rigging up a 12-volt wire straight to the compressor clutch. Just don't drape the hot wire into the exhaust system or get it into any moving parts; it isn't going to hurt anything to run it this way for a while to test it. If it cools, your tech needs to come back with that 17-page bulletin and a good multimeter to find what's wrong with the HVAC electrical. If it doesn't cool, your tech didn't get it right with all of those parts replacements and there's still something wrong in the sealed system. The system pressures would show this!!
Edited by Redwrench 5/4/2014 11:43
| |
|
MX 240 cab air.
