Big truck a/c help

parkerFly · Post by **parkerFly** » Sat Jul 23, 2016 11:30 am

I have an older semi that has a weak a/c system and does some funny things. The previous owner told me it didn't work well and 60 degrees is as cold as I can get it. It has a brand new York compressor, dryer and expansion valve. I flushed the system and pulled a vacuum on it for about 3 hours. The condenser is a big wide open type and is very clean. The evaporator looks to have been replaced not long ago and is very clean. Doing all that didn't help anything and when I'm on a long run down the interstate it will warm up to 80 degrees, but cool back down to 60-65 when I idle. I pulled the system back down and vacuumed it again and replaced the dryer and expansion valve again and no difference. My high side is around 250 and low side 35 or so. No idea what it's doing on the long runs but the fan turns off and kicks back on at idle and stays on until moving again.
Does anyone have any ideas why it won't blow out any colder and warms up on long runs? Thanks

Justin

Post by **Tim** » Sat Jul 23, 2016 11:34 am

What's the low side pull down to at high idle. For an TXV type system, 35psi seems a little high.

parkerFly · Post by **parkerFly** » Sat Jul 23, 2016 11:40 am

Going off memory I think remember seeing it 25-30, but I could be wrong I didn't pay close attention to that. I have no idea what the capacity of the system is, plus it's had a sleeper unit added that shares the freon so no real way to find out either. Thanks

mk378 · Post by **mk378** » Sat Jul 23, 2016 1:27 pm

Getting warmer on a long run could be evaporator freeze-up. Pull over after a while and check for ice on the lines.

If the sleeper TXV is stuck open it's going to interfere with operation of the front unit. Make sure the new front TXV is properly installed with the bulb attached to the evaporator OUTLET line and well insulated.

Are you sure you're charging in enough? If you have found a spec for the charge amount, is it with or without dual air? An old truck system can need quite a lot compared to a newer car.

parkerFly · Post by **parkerFly** » Sat Jul 23, 2016 1:36 pm

Interestingly enough a friend of mine just ran into a guy who has worked on a lot of these old trucks and he said I have it overcharged for a York compressor. He said run the low side at 25-30 and high side at 175-200. I've never heard that but like I told him I'm willing to try anything.

bohica2xo · Post by **bohica2xo** » Sat Jul 23, 2016 2:34 pm

High side pressures have a lot more meaning with an ambient temperature to relate them to.

Have you checked the oil level in the York?

.

parkerFly · Post by **parkerFly** » Sat Jul 23, 2016 2:43 pm

The pressures I've been getting are at 90-92 degrees. I have not checked the York's oil. It was supposed to come pre filled and I took them at their word.

bohica2xo · Post by **bohica2xo** » Sat Jul 23, 2016 4:00 pm

You have described a large system with dual evaporators & TXV's.

You should check the compressor oil level the next time you de-pressurize the system. Most of the oil stays in the sump, but some winds up circulating in the system. On a large system, this can pull the crankcase level down. Here is the service manual on the York:

http://www.tccimfg.com/wp-content/uploa ... 12-16P.pdf

I would put the gauges on the truck, pull up high idle and check the discharge temps on both evaporators as well as system pressures.

Big truck a/c help

Big truck a/c help

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