Checking AC in cold weather

[bittan]

What's the minimum outdoor air temp you would recommend checking the AC. I've typically known it to be about 70. If its colder outside, has anyone ever wrapped plastic around the cond coil to raise head pressure to read your gages. This is something I've been TOLD to do where I'm working, but I really question it!

[billva]

what temp. are you going to simulate by wrapping the condenser (or disconnecting the ofm). that is an unknown, so you will not know if pressures/temps are correct.

minimum of 65 degs. 90 better.

[BobbyBJr]

Age old question...lol. I have read manufactures data recommending putting plastic around the coil to get the condensing temp up to 90º F, so it is plausible to do from time to time. I have done it myself a few times, but I wouldn't make it a habit. In all honesty, sometimes you just have to do what you have to do to complete the call and none of us can control the weather.

Bobby

[danj]

When possible, cross check using at least 2 methods. Start with a charging chart in the unit. It has its limitations though, if your air flow is less than 400 CFM per ton(most are ) and your line set is different than listed, these can effect the charts accuracy. Next, look at superheat and subcool. If your super heat is high, you would also expect your subcool to be high.(the outdoor coil storing refriderent). The superheat may be high when the ambiant is low. The cooler outdoor temerature results in lower operating pressures. The lower the liquid line pressure, the less refridernt the indoor metoring device can move. If you have subcool of 15-20 degrees, you have plent of charge in the unit. If your superheat is also high (20-30 degrees)try driving up the dicharge pressure(disconect outdoor fan ) and watch your superheat come down, as the indoor metoring device starts moving more refridgerent.
(Thats from Dayrl)

[Edited by danj on 04-27-2005 at 11:23 PM]

[bittan]

Thanks for the info!

[koolitman]

TO BE SURE I weigh in the charge so i won't have to come back in warm weather