Hey guys, I’m new to this forum and I ran into some issues with my ac compressor. I’m not getting any power supply to the compressor or the pressure switch and relay on my cat 299 D3 XE. I have power coming to the fuse box on both fuses which are 20 amps but not directly to my ac compressor. I was hoping someone had schematics because I can’t trace the cables coming from the fuse box. Or if there is another relay or switch going bad or a cable might be stripped and that is stopping from sending power to the ac compressor to complete the circuit. Any help would be appreciated.
Do you have the serial number handy?
Yes sir, CAT0299DEBX900888
A schematic to cover your Serial Number is in your message inbox.
I have got the same issue with my 299 d3. cat0299DADY905260 can you send me the ac schematic? thanks
Check your message inbox.
I'm having a tough time figuring out the problem. ac blows , ac light comes on, high side has 12v, low side nothing, temperature control switch tested open I jumped red and white no result. ac relay seems to work but I don't have voltage for the compressor.
A/C pressure switches are designed to protect the compressor in the event of low or high pressure condition. The ECM looks for voltage on a certain pin to confirm the system is healthy before engaging the compressor/relay. Pressure switches do go bad. Systems leak and sometimes they are over filled with coolant. If any one of these conditions exist, the compressor will not engage. Jumping an A/C compressor relay or connector pins can be costly. Limit it to short bursts (seconds) of jumpering. Your machine should be throwing related codes as well.
I'm not getting voltage to the relay for the compressor. compressor does run when I supply 12 volts to it. is there another fuse or relay that sends power for compressor?
Not to step on Nige here, but you do have the wiring diagram specific to your machine serial number? Assuming you do, find the compressor and work backward looking for pressure switches, fuses and relays. If Nige sent it to you, the diagram has hyperlinks embed that that you can click on to move around the diagram.
He does. See my Post #4 above.
there has got to be a fuse or relay that's not sending power to the low side switch and the compressor relay. I,ve chased the schematic backwards from the relay. but I don't see any. I read that there is another fuse panel behind the cab but I can't find it.
I,ve got power at the thermostat switch. the switch tested open. so i jumped it across power and signal. nothing. at the relay I,ve got power on the white signal wire. but i get 2.5 on the other one which maybe ground from ecm? I see that the power for low side and compressor power is tied together but I can't tell whether it's and fuse or not.
You mean the one inside the engine compartment on the back side of the firewall..? See Page 10 of the schematic. It's shown as Item 46.
searching backward from the compressor relay. do you see a fuse in that Circuit? A510-AR9 OR-14 is missing power.
ok, I have added some freon by supplying the compressor with voltage. then plugged the low side back in. the compressor runs. it started to cool some but then seemed to lose charge. now the compressor cycles off and on. high side made it to 150 low side was 65-70 running. just sitting here machine off i'm getting 50 high side and 65 low side. is that signs of a clogged orifice ? or accumulator?
Short cycling compressor indicates low pressure or high pressure safety switch thresholds are being exceeded. Static pressure (not running) should be approximately the outside ambient air temp. Gauges have a line on the face of them that corresponds to c/f ambient temps and the static freon pressure. Leaks can be simple or complex to locate. Sometimes we get lucky and its a failed Schrader valve. Other times we look for oil stains (wet dirt) on ac hose connections. And sometimes, coils fail. Again oil stains are typically obvious but can hide. Initial indication is that due to the fact that your compressor cycled and some cooling was present, it says that your leak is more the issue than a clogged tube or regulator valve failure. This armchair diag is based up on your system not being overcharged… With gauges connected and reading pressures, refrain from opening the right valve on your gauge set. It immediately equalizes high and low pressures… lots available online about that as well. Respective Freon pressure charts are readily available online as well. As are troubleshooting technique's.
does anyone have the hvac hose assembly schematic. I have found a leak at the firewall. I,d like to know what type of end is on the high side line. 435-8934 02
cat0299dady905260
The illustration below is one end of that Part Number of hose. I think the second illustration is the other end.
I have no voltage to my compressor. My charge pressure is good once I manually apply 12v. What did y’all figure out?
First thing you will require is an electrical schematic. Please post a machine Serial Number.