Hello. New to the forum today. I have a 277b and the air conditioner is giving me trouble. It started to work intermittently and now is not blowing cold air. I vacuumed and recharged the system, but no change. The fan was only working on high, so I replaced it and it is still only working on high. Does anyone have an electrical schematic for the air system that you could share? I would like to fix the fan issue first and narrow down the air problem afterwards. Greatly appreciated! Thank you.
Gauge readings? Which fan? Complete vac down with no loss after 1 hour? Machine serial number?
I have no guage readings to report. The fan in the cab, under the heater control panel. Yes, vacuumed down for over an hour and the guages stayed put after turning off pump. *CAT0277CMDH00396* ***The air conditioner was installed by caterpillar soon after purchasing the machine new. Thank you.
Check your messages. Electrical schematic in your inbox.
Great. Thank you!!
My 248b would fail condenser fans. A PITA to change the first time, as the fan's nuts require the shroud to be removed. I used fender nuts (U-nuts) the second time. The fans should run any time that AC is selected and the blower is on. Assuming that they are not coming on, simply unplug one while the AC is on and test the connector for voltage. Then, test the other.
I had a chance to get back to the machine today. With the machine off, the guage readings show 85 on the low side and 100 on the high side. When the machine is running at idle with the air conditioner on high, the readings are the same, however when I go to full throttle, the low side drops to 75 and the high side rises to approximately 115. The air is only slightly cooler. Both condenser fans are operational. Any thoughts?
Someone will correct me shortly,,, Low and High pressure should read the same at rest, somewhere around 100-110. When compressor engages, Low should be around 30 and High side no higher than 250. If pressures have not much difference, I am guessing your compressor is not pumping like it should. Unfortunately, you should replace compressor, drier, and orifice tube/expansion valve after you have flushed the system very well and pull and hold a vacuum for at least 30 minutes. Some one will either verify or tell you correctly.
The fan blowing high all the time is usually the fan speed resistor. Usually mounted in the plenum air flow. You should make sure your compressor clutch is actually engaged when AC is selected. It will free wheel on bearing until you activate AC, then gets drawn together to drive compressor. You could have a faulty AC relay, or bad wiring going to relay. One quick test is to jump PIN 30 to 87 in relay connection and check for voltage down at compressor, or see if it engages.
If compressor is engaged, and the pressure change is only minor, I'd suspect the expansion valve, not the compressor.
Hey everyone, Ok I was able to circle back to this issue. I still have no cold air. I separated the hydraulic motor from the ac compressor to confirm that it is turning. The hydraulic motor turns, and what surprises me is that it turns whether the AC switch is activated or not. I assumed that the solenoid on the motor was there to open and close the flow. Now I am confused. Can someone help me understand? Thank you. Jeff