AC questions

[fireguywtc]

For those that are interested in pictures, I finally got around taking some. Mainly of the new condenser and under the hood. I neglected an interior pic because it is all stock.

[1972hiboy]

I owuld think it should cool down to mids 40s vent temps

[basketcase0302]

fordman on Thu Jul 21, 2011 10:04 pm
i dont want to derail this thread. but i wonder if there are some sort of charts for sizing condensors for our systems or other systems.

ok now back to the show. when my factory air was working. it cooled. but you could still feel the heat from the enigne in the cab.

Bill,
Craig might have a good point here. Maybe the A/C is working fine, possibly heat from the heater core / heat from a vent / heat from the engine compartment / or?
It would usually be just the opposite as far as cooling. It would normally get colder as your RPM's increased.
The install on the compressor looks real nice and clean!

[fordman]

i'm at a lose here. my 68 factory air never has cooled my truck very well. it gave you cool air but the truck was always hot with a blast of cool air from the vents. it felt like to me that the engine or exhaust heat was coming from the firewall and into the cab. . but i had no holes in my cab at the time i was driving it.

[fireguywtc]

Okay, the saga continues and here is what I have firgured out today. I have no pressure regulation for my low side pressure. Probably affects the highside too but I dont have a high pressure gauge. I need some of some kind regulation. Today I hooked up a gauge to my low side valve and checked it out. Outside temp was about 100* (and it was 7pm ) and at idle the pressure was about 40psi. I reved up the motor several times and noticed each time I did, the pressure would drop. The higher the rpm, the lower the pressure. At 1500 rpm, my lowside pressure was about 22-25psi. At 2500 rpm, the pressure went to about 10psi. 2500-2700rpm is my cruising speed around here. As soon as I lower the rpm or idle it, the pressure would increase.

This would also help explain why at idle my AC cooled pretty good and going down the road it would not blow as cold. Does anyone have any ideas on how I can regulate the pressure? I am going to need to do something. So far this summer we are on day 72 of over 100* and there is still no relief in the forcast. Makes me sick.

[fireguywtc]

Bring up an old issue. This summer my A/C is still giving me fits but I think I might know what the problem is: the expansion valve since it is the only thing I have not replaced on the system. This summer any time I drive with the A/C on with the highest fan setting, the evaporator freezes. The tubes on the end get covered in ice. Taking measurements on the system at idle the highest suction pressure is 25 (at idle) with the lowest at about 15 psi (2500 rpm). when the ambient air is in the high 90s the high side is around 300.

I am pretty sure the expansion valve is not working correctly, stuck in the "closed as much as possible" position and that is why I cannot get the suction pressured higher. Does anyone have a source for a new/refurbished expansion valve for the factory A/C because they are obsolete. If not does anyone have a good working one I can get?

[basketcase0302]

Bill,
The pressure will drop as you increase the RPM's normally. Too hard to even remotely put a number on what your gauge should be reading-far too many variables to "guess" that 25 would be low. And yes, low on gas will be the first thing to cause it to freeze up, (as well as a bunch of other things too). It would be a real good thing to take it through a shop and tell them you want a sub-cooling refrigerant charge / measurement done on the system. Call around and request prices for a few shops to do this. By verifying the sub-cooling you'll do two important things.
First, you'll verify the system has the right amount of refrigerant in it.
Second, this method will also verify if the TXV is opening and closing as it should.
I didn't say this....but you can also take a wrench and tap on the TXV when the system is operating to sometimes free up a stuck diaphragm inside one.
Just don't "beat" on it!
And maybe try to contact these guys-they wrote the book on refrigerant metering devices.
Might had even made them for our trucks then stamped Ford on them, (but I'm no parts monkey so don't take that to heart).
http://www.sporlanonline.com/
Sorry I didn't see you previous post last year!

[flyboy2610]

This summer any time I drive with the A/C on with the highest fan setting, the evaporator freezes.

I have read somewhere that you shouldn't use AC with the fan on high, because the air will be moving so fast it can't properly transfer heat and cold air from the evaporator. If everything is working the fan on a lower setting, I would leave the fan on a lower setting. Your AC will actually cool the cab better.

[fireguywtc]

There are two reasons why I believe the TXV needs replaced: last summer I didn't have this freezing problem with the same charge and, since the freezing started I added 24oz of R-134 which raised my high side quite a bit but did virtually nothing on the suction side. I understand that the pressures will drop when the engine revs, makes sense. But I don't think it should be so low.

I will try tapping the TXV with a wrench again but I believe it will only mess up again, probably soon.