I suppose I read too much..

[troyport]

Call me crazy, but this HVAC stuff is very interesting. I spend a lot of time here reading posts. Anyway, if removing moisture from a system can be done easier the higher the temperatures are... does anyone run the customer's furnace while evacuating? This would bring the evap temp up to 120 degrees or so, wouldn't that make things easier? Or AM I nuts? Don't answer that last question. Thanks, Mike.

[comfortdoc]

If there is moisture in the evaporator it will help. Keep in mind most of the time, that scenario will happen in the summer whn it is HOT outside. The homeowner will not appreciate the heat running into an already warm house. May also trip the limit if the house is excessively warm.

[hvacvegas]

Call me crazy, but this HVAC stuff is very interesting. I spend a lot of time here reading posts. Anyway, if removing moisture from a system can be done easier the higher the temperatures are... does anyone run the customer's furnace while evacuating? This would bring the evap temp up to 120 degrees or so, wouldn't that make things easier? Or AM I nuts? Don't answer that last question. Thanks, Mike.

Your not crazy. Done it before.

It's actually kinda weird. You'll turn the furnace on, and your moisture reading goes up. Then it goes down like a rock.

Sometimes when you do a compressor replacement, a receiver will be full of liquid refrigerant, so you can leave for a bit while it pumps, or hit the receiver with the torch.


But yeah, it works.

[jaypslugger]

Often use a heat gun but be careful; they can remove paint.

[motoguy128]

Not a bad idea to speed up the process a little. Do furnace start-up first while pumping down the AC unit.

120F is only a 50F temp rise, a lot of system will be closer to 125-135F with 70F return temp if it runs long enough. Some modulating furnaces will reach almost 145F in lower stages.

On larger commercial/industrial chillers the ONLY way to get all the moisture out is to add some heat. The last one we we used a little 120VAC residential water heater and a small circulation pupms. it still took 3-4 weeks to get all the moisture out. Yes, that's weeks... not hours or days. The chillers was completely flooded.

[troyport]

Okay, thanks for the reply. My thought process was this: The tech is coming back on Saturday to evac, but since we are at the time of year where the furnace does not run much if at all, the basement, where the evap is of course, is quite cool.. So I thought I would sacrifice a little propane and run the furnace while it is being evacuated.. Maybe help the guy out and get a better result for me. Mike.

[motoguy128]

I'd let him do it. The result should be the same either way, just speed up the process a little. There's usually enough installation work to be done, that you set the vaccum pump, then work on the wiring, finish any sheetmetal work, go get lunch, etc. Remember that when you get near a full vacuum, water flashes off pretty rapidly whether it's 70F or 130F. Sure, not as fast, but still pretty fast.

Keep in mind that most furnaces should not be run with a return temp over 80F and condensing furnaces which use outside air, and outside air temp of 80F.