I've got a 420E that I'm working on. I done a whole bunch of repairs to it, I adjusted the throttle cables becasue they have stretched and my high idle was only at 1900-2000rpm. I now have it sitting at 2100+rpm on foot and about 2400rpm on hand. once I did this adjustment if I run the engine without the a/c on it runs great! If I have the a/c and then rev the engine up it squeals holds the rpm guage back and then once its stoped squeeling the rpm guage goes up to what I have it set at and it runs ok. I checked the belt and it was a bit loose so I tightened it. it went from squeeling at the start to rising ok to around 1300-1500rpm squeeling holding the rpm and then letting it move up to high idle...I checked the alt and a/c pulleys and neither actually stop when this happens. If I run high idle with a/c off and then flip the a/c on while at high idle theres no problem and it blows nice cold air. I'm wondering if the compressor clutch is starting to go, it was ok at the lower rpm but now that i've bumped it up its affecting it? is this gonna turn out to be sacrifice rpm speed to do away with the squeel? Unfortunatly I don't have access to a photo tac to check rpm off the fan I'm only able to go off the rpm guage in the cab. any thoughts suggestions help would be appreciated!
I'm having a little problem following your question but since the engine seems to be loading down it may be that the compressor is starting to lock up. It could also be the A/C pully bearing getting ready to seize which is a slightly different problem from the first one I mentioned. Sometimes this bearing can be replaced without replacing the compressor. Could it be that the belt was just loose and everything is ok now?
high idle should be 2310 +-40 rpm. If you can get high idle with the handle and not the pedal then the pedal linkages is prolly worn out. The squealing sounds like the belt is slipping with the load of the ac applied. I would replace the belt and check the pulley for wear.
Sorry, I guess I was trying to ask is it the compressor on its way out, or is it something else I'm missing. When I worked at the cat dealership i never had to do anything with A/C much... I had wondered if it was the compressor or the bearing just starting to go, was fine before cause the rpm wasn't up to par but now that it's higher its spinning faster etc... thanks for the spec, since I stoped working for cat I don't have access to all the specs and such anymore. lol via the incab rpm guage I've got the handle maybe a tad high (2400rpm) and the pedal(just over 2100rpm) a bit low...I wouldn't be surprised if all 3 need to be replaced...the machine has 2100hrs, used in landscaping and snow removal, its probably about due for them....I'm just trying to get things better than they were without having to spend the $700+ for the pedal and both cables...if i can get it to go until the winter or next spring that's fine by me...lol all its really gonna due is make digging a little slower and roading the machine a bit longer to get place to place...I guess I'm gonna have to go out and buy a photo tac.....any suggestions on what ones to look at, what ones to stay away from? I will suggest that to them, i guess while doing this one i might as well do the alt belts as well since they are cracking. i just find it weird that it gets stuck at 1300-1500rpm and then goes...I've worked on 420's before many of times just haven't had to do much at all with a/c...
The compressor does pull harder at a higher RPM because of more head pressure, so maybe it does make sense. I read your original post again and I gave you some bad info. It can't be the compressor pully bearing cause that would make the belt squeal even when the A/C is off.
If you haven't tried checking the pressure in the A/C system, i would try that. My Ford F-350 A/C does that squealing just about every year. And when i check the pressure, it is a little high. When i relieve some of the pressure it works just fine. Why it keeps building pressure is beyond me. All i can figure is that altitude or changes in altitude have something to do with it. That plus the fact that the truck is 24 years old. lol Joe
You could try cleaning the condenser coil to get the high side pressure down. I like aluminum cleaning chemicals to finish the job. If you put pressure gauges on it get the temps on the high and low side also, outside air temps and vent temps too.