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Charging 93 mustang

webbch on Sat July 19, 2008 7:51 PM User is offlineView users profile

Year: 1993
Make: Ford
Model: Mustang
Engine Size: 5.0 L
Refrigerant Type: R12
Ambient Temp: 73

I got a little confused while charging this 93 mustang. It's my first major a/c system repair. First off, it has all new lines, the evaporator and condenser were flushed, compressor was flushed with mineral oil. I drained the compressor, and put back 5 oz of mineral oil in the compressor, 3 oz in the evaporator (system oil capacity is specified as 8 oz total). I pressurized the system with nitrogen to 150 psi and it appeared to hold steady for an hour. Pulled a vacuum down to 500 microns and it slipped up to 1500 microns and held for over an hour.

I charged per the factory label to 34 oz (using tank and electronic scale), while it was 73 °F outside. It started cooling pretty decently, the high side pressure was 180 psi*, but the low side pressure kept dropping below 20 psi, which I believe is about the setpoint of the low pressure cutoff switch, so the compressor would shut off. Vent temperatures were 48 °F. I took this to mean I must still be low on refrigerant, and checked the capacity listing in the FAQ section of this site, which states 40 oz. I added an extra 8 oz, putting me to 42 oz. total (don't ask ;-) . Vent temperatures dropped to 41 °F, the low side came up to 22 psi, the high side to 195 psi, and the low pressure cutoff switch stopped turning off the compressor at 1500 rpm.

I thought that I'm trying to get closer to 30 psi to avoid evaporator freeze up, and my high side still seemed reasonable, so I tried adding an additional 1.6 oz of R12, which had no effect on vent temps, but brought the low side up to 24 psi, and the high side to 200 psi.

I repeated this adding of 1.6 oz two more times until I felt quite uncomfortable about adding any more, as I now had a total charge of about 47 oz. Vent temperature went up slightly to 43 °F, but low side pressure got up as high as 25-26 psi, and my high side was 212 psi.

In addition to this, the whole time I was getting a LOT of condensation on the a/c lines on the low side. I don't have a measurement of the humidity, but it was quite balmy for Arizona. I would guesstimate at least 80% humidity. I expected a fair amount of water coming out of the evaporator condensate drain, but did not expect so much moisture on the lines themselves. Is this normal?

Also, am I correct in shooting for a low side pressure of about 30 psi? My high side pressures are about as high as I think they should be now, given the ambient temperature, so I'm hesistant to add any more refrigerant. Just would like a second opinion from folks with a bit more experience. Thanks.

Chad


*Pressures measured at 1500 rpm, ambient measured at 2" in front of condenser.

Chick on Sat July 19, 2008 8:17 PM User is offlineView users profile

You may be overcharged which will show once your ambients go above 80 degrees, always go by the label on the car, as long as you are using virgin R12 and not something that has a 12 in it.. A few ounces more won't hurt, but watch the high side when it gets hot outside... 73 isn't that hot...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

webbch on Sat July 19, 2008 10:40 PM User is offlineView users profile

I agree - 73 isn't that hot. Yes, it was virgin R12. I'll take out a few ounces - you reckon it was OK that the compressor was pulling down to 20 psi when I charged to the sticker capacity, and activating the LPCO switch (because it wasn't real hot out at the time)? I thought that was a sign that it was low on refrigerant.

How about the "excessive" condensation on the lines (lots of full droplets on the lines)? Is that normal in humid weather? Plenty of water coming out of the condensate drain from the evaporator as well. Thanks.

Chad

Chick on Sat July 19, 2008 10:47 PM User is offlineView users profile

Yes, sweating is normal in humid weather, just like the dripping under the car on humid days.. The cycling is normal to keep the evap from freezing..It will do it more when MAX air is used rather than fresh air which is hot, inside air recirculates already cool air..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

webbch on Mon July 21, 2008 10:35 AM User is offlineView users profile

I removed 10 oz, which puts me halfway between the sticker charge and the capacity tables. Not a problem with how it cools. I then went and checked my '90 silverado (accumulator system as well) that's working quite well, and verified the sweating. There's just lots more hard lines in the mustang, so it was apparently a lot more noticeable. Thanks again for your help. It's much appreciated.

Chad

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