Roadmaster AC.. Now with Variable Orifice!

You should know what this is. If not, you probably roll your windows down a lot.
Fast_Ed
Posts: 550
Joined: Wed Oct 23, 2013 9:45 pm

Roadmaster AC.. Now with Variable Orifice!

Post by Fast_Ed »

I spent this weekend wrestling all of the steering components out of the Roadmaster, and installing new. More on that in a different post. But while the car was at Firestone, I was able to get the refrigerant evacuated from the AC system. The cost was 42 dollars and change; well worth it to avoid opening up new holes in the ozone layer.

I pulled out the old orifice tube, which looked like this:
Roadmaster Orifice Tubes 160802.jpg
Yeah, not great. But maybe that's just the stuff I missed when flushing last time. Anyways, I didn't flush it this time. No time for that. I'll probably just do this same thing every couple years... Using the orifice tube as a filter.

I added 3.5 oz of PAG to the new accumulator, installed the VOV and vacuumed the system just in time to have to do something else. Came back to it two days later (today) to recharge. Most of the vacuum was still there. I probably lost some when disconnecting the manifolds, so I'm ok with that. I vacuumed it back down for another ten minutes and then began to charge, being careful to purge the feed (yellow hose) and keep the vacuum on the other two.

The compressor started to kick on with something like 1oz of refrigerant, so that tells me that cars that are short cycling must have very very low refrigerant. This car takes 28oz. It took about 9 minutes to add all the refrigerant ( I know this because I had to run a stopwatch, waking up the scale to keep it from going to sleep during the charging.)

Once the charge was completely installed, I capped off the system and took a video of the pressures... Can I post a video here?
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by kevm14 »

Upload to youtube and link.

Also I bet my VOV looks like your FOT. Those are real acronyms so don't laugh at me.
Fast_Ed
Posts: 550
Joined: Wed Oct 23, 2013 9:45 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by Fast_Ed »

I just realized I'm too lazy to download a video from my phone.

The rundown is this:
Ambient temp shown on roadmaster is 74F.
Low Side pressure:
Compressor kicks on at 40psi. Kicks off at 20psi.

High side pressure:
Lowest is around 125psi. Gets up do 260psi before the secondary fan kicks on.

When the secondary kicks on, the pressure drops way down to 20psi low/125psi high. Very quickly.

My vent temp after all this was around 50F. I would have liked to see it lower, especially with such a low ambient pressure. I also would have expected the secondary fan to kick on at more like 210 psi. Is there an adjustment on the high pressure switch like that on the low pressure one?
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by kevm14 »

Computer controls the fan so, no.

50 huh? That doesn't seem right. I wonder if your heater door thing isn't fully going to the cold setting or something dumb like that.

You could try with a stone cold engine (cold heater core) and see if that changes anything I guess.
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by kevm14 »

40/20? Did you adjust the low pressure switch?

40 psi equates to a temp of 45°F and 20 psi equates to 22°F. Something isn't right there. Your temps should be ice cold. And freezing the evaporator even.

Also, is the compressor cycling through all this, at idle engine speeds?
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by kevm14 »

I can't seem to find the pressure thresholds for the secondary fan. Sadly I may have to find and fire up my old tuning Dell and get the values from my Fleetwood calibration.
Fast_Ed
Posts: 550
Joined: Wed Oct 23, 2013 9:45 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by Fast_Ed »

Oh no, not the blend door!!

I don't know where that is... I also didn't realize that those pressures directly correlated to temperatures... I didnt adjust the switch, but I did think that 20psi seemed very low.

I did notice that the center ash tray gets very cold during AC operation.... Maybe you've got something there.
Fast_Ed
Posts: 550
Joined: Wed Oct 23, 2013 9:45 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by Fast_Ed »

Yes, the compressor was cycling on and off.. In the video I took, It went from 40 PSI to 20 PSI in around 50 seconds...
Fast_Ed
Posts: 550
Joined: Wed Oct 23, 2013 9:45 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by Fast_Ed »

Update: The AC is very noticeably improved from before. Today we took a trip to providence, followed by some parking lot idling, etc. 75-80f ambient, closer to 80 toward the end. Vent temp actually went down to 40 when idling in the parking lot. It appears to be between 40 and 45 when around town. And 40 on the highway.

It could just be variation in the vov... but it was more than cool enough the entire time. Almost no waiting for cold air at initial startup either. Time will tell if the vov is durable enought for long term use. My initial reaction is that it is probably worth occasionally replacing it for this performance.

Adam should definately perform this mod to the Fleetwood. A set of o rings at the same time would make it awesome.
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: Roadmaster AC.. Now with Variable Orifice!

Post by kevm14 »

It's a good thing you thought of the VOV.
variation in the vov
lol

Honestly I should replace mine except my car still holds a charge. Not the original charge but damn it's been probably 10 years now since I did that last service and it's still on the original compressor. Plus it has Freeze-12 so I'd have to do an official R-134a conversion. Not sure about oil compatibility and stuff...
It appears to be between 40 and 45 when around town. And 40 on the highway.
I would still expect colder. But, if you are happy with the performance and comfortable, then I think you're doing alright. Does it maintain 40 with the compressor cycling? That's the issue with mine - when the compressor cycles (like on the highway), the vent temps fluctuate quite a bit. Otherwise my A/C works pretty well and I can get vent temps well below 40 but I also fooled around with my low pressure switch adjustment (had to with the Freeze-12 anyway).
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