Powering Coach AC While Engine is Off

[buswarrior]

In 100 degree heat, Washington DC, one summer, it took all the old school tricks to keep a DL model acceptable waiting for the church group of seniors.

It was struggling when on the fast idle. Driving, it caught up fine.

Find a big enough parking lot and head for the back, park bum to the sun, no sun load on windows, fresh air closed up, all of it running on high,  main, driver's and parcel racks, all overhead gaspers open.

Dangerous game, when an idling ticket cost $300 in those days.

Happy coaching!
Buswarrior

[Jim Blackwood]

Good info.
So if the compressor puts out 4 tons at 2000rpm my guess would be half that at idle maybe? It sounds like the compressor might have been seriously undersized for the rest of the system which hardly makes any kind of engineering sense that I can see. It leads me to question either the output specs of the compressor, the cooling requirements of the coach, or both.

Jim

[buswarrior]

Go ask Carrier?

It's their systems, they'll know why they did whatever they did.

Happy coaching!
Buswarrior

[jap42]

Go ask Carrier?

It's their systems, they'll know why they did whatever they did.

Happy coaching!
Buswarrior

Carrier made the compressor and I think the condenser. The Evaporator was a different company and most of the other parts. Carrier did not design the system, MCI did.

I am thinking the TXVs and compressor are sized to work well (Not Effeciently) at running speed without failing at high speed. Maxed out going up a hill I could see the RPMs getting high enough to get 10 ton out of the compressor. Infact when I do the compressor stops due to high pressure and I get an A/C Malfunction light, usually just before 4th gear on a slight incline. I think this was due to the MO99 that had replaced the R22. Since the 407C it does not happen any more. But that would suggest we were getting close to the limits with R22/R407C

I truly think this system averages 36-48 going down the road, Maybe a little lower at idle.

[Jim Blackwood]

What did you have running at the time, just the main evaporator? Because that TXV is 10 ton and if the dash and rack airs were on, based on the TXV used that is another 4-1/2 tons of evaporator.

Jim

[jap42]

I dont have the Rack Units, So Main, and Drivers. I think the MO99 runs a little higher discharge pressure then the R22. My guess is the R22 was right at the high limit switch. So the MO99 pushed the discharge pressure over the limit. Again, only at really high RPM.

[Jim Blackwood]

Good info.
So what is the max RPM that the series 60 will normally run in a bus? (I don't have a tach)

Jim

[jap42]

Lol, I dont have a tach ether, It's not very fast... 2100RPM according to wikipedia.

[Jim Blackwood]

Maybe Carrier has a performance curve for that compressor?

Jim

[jap42]

I can not find one, there definitely would be, considering its variable speed.

Based on my reading TXVs can typically throttle down to 35% of their rated capacity. So that 10Ton TXV should be able to throttle down to 3.5 Tons. That might explain why its so large. So It can handle the full range of the compressors capacity.

[Jim Blackwood]

Makes sense. Then the dash and rack TXVs should be able to go down to 1/2ton each, if they are switched on. Sounds like the compressor is the limiting factor.

Jim