No A/C in the City

[ford33]

So how does this relief valve work? Is it supposed to release refrigerant if the system is over-charged?

 

[saewoody]

I apologize if I missed it somewhere, but if the condenser were clogged with debris, that would also affect the airflow through it. This would cause your A/C to not work as efficiently. I spent several minutes with a hose on mine today since I can easily hit it form both sides with the engine out. Good luck.

 

[jcwaters1]

There is always some friction in the fan clutch which keeps the blade spinning along with it, even when it's "seeing" cool air. So, the fan does move some air when the engine is still cold, but very little.

The calibration built-in to the fan clutch should be such that it is intended for use with an air conditioning equipped vehicle. If the clutch is not operating at it's design level, this can account for poor A/C performance. Generally speaking, if the weather is hot, that is, ambient air temperature is fairly high, perhaps 80^ F. or more, if the engine is allowed to sit and idle with the vehicle standing, if the fan clutch is not up to par, the engine will overheat. If it does not overheat under such conditions, chances are the fan is doing adequate cooling to operate the A/C fairly well. imp

so what might my problem be? any ideas?

 

[97 EB Mike]

Let's be sure of definitions here. "Coolant" is the stuff in the ENGINE. Refrigerant, or 134a, is the stuff in the A/C system. Surely, a low level of either will cause malfunction of the engine, or the A/C system.

Right... and yes, a malfunction would be expected. But what malfuntion (in the ac system)? I would have thought a low ac system would have the described symptoms (which does not appear to be the case).

I only referenced the engine coolant system because the 2 seem pretty similar in function to me, and if my truck overheated, the first thing I'd check is fluid level, which is what made me think low refrigerant earlier in this thread. Sorry to have muddied the waters...back to ford33's ac system

 

[Gus Gorilla]

97 EB Mike. The theory is sound for engine coolant but not really for refrigerant which is a much higher pressurized system. When the coolant is low it keeps moving through the radiator. At a higher speed more air flows and it can dump more heat out into the radiator because of the air movement. The pressure of the system does not dictate the heat removed the same as it does in an AC.

For refrigerant if the system is undercharged there is no "empty space" such as air in a radiator. It is still a pressurized and completely closed system. It will pull the low side too low or even into vacuum. There is a low side pressure switch to prevent this. When the low side drops under roughly 32PSI it creates evaporator temps at or below 32 psi and causes freezing. All the condensation freezes(on the outside of the fins, not inside the system) and cooling in the car will all but stop.

So technically you could under charge the system, bypass the low charge switch, and constantly run the compressor and have low pressures at 10PSI making your evaporator around 10F. It would be awesome for about 3 minutes. Then freezing, then no more A/C till it thaws.

The cycling is a necessity of operation and an undercharge doesn't let that happen correctly. In the radiator better cooling happens because of airflow and increased coolant flow even with less coolant. In the condenser it's pressurized and already full. More airflow makes better cooling but adding more refrigerant will not "fill up" the condenser. It's already full because the compressor made it that way.

Damn that got long winded and muddy. Sorry.

edit: the symptoms of an undercharged A/C is quick compressor cycling or no operation at all. As well as no or very poor cooling.

 

[Gus Gorilla]

Ford 33.
The relief valves need a certain PSI then they "pop off" and vent the refrigerant into the air until pressure comes back into range. They usually open around the 525-575 PSI range and then close again when pressure gets down 425-450. You'll know if it happens. It's a shhhhhht sound and can look like a small fire extinguisher just went off under your hood. Plus it makes an oily mess on everything around it. If you have dye in the system the blacklight will make it look like a disco.

 

[97 EB Mike]

Damn that got long winded

lol...that's actually the piece of knowledge I was missing. Makes more sense now, thanks

 

[Gus Gorilla]

I'm glad it made some sense. I had to go lie down after that one.

 

[Gus Gorilla]

JCwaters, yours might be normal. You just have the cooling fan running all the time right? That won't hurt anything.

 

[ford33]

Well I'm glad to be on this forum, you guys have a lot of knowledge

I added refrigerant today, although the air seems to be slightly cooler, this didn't solve my problem either. I have noticed that as long as my rpm's are 2k and above the air feels cold, not as cold as I would like, but cold. Assuming this still points at the condenser? What can I do to help that condenser out?

 

[jcwaters1]

JCwaters, yours might be normal. You just have the cooling fan running all the time right? That won't hurt anything.

so why might my "A/C" not be all that cold? i've recharged it twice, and it doesnt feel as cold as it could. it will cycle, when the compressor is on, its cold, but then it shuts off after like 10 seconds and it gets warmer and warmer until the compressor comes on again. which is 15 seconds or so. it seems like it cycles on and off a lot.

 

[Gus Gorilla]

FORD33
Yeah, it could still be airflow. Higher RPM normally improves cooling. Even for a perfectly operating system. I can feel the difference in my ST easily. It increases airflow with the fan and creates better pressures with the faster moving compressor. Get a gauge on there and measure running pressures. You could get a fairly cheap Harbor Freight set and become your friendly neighborhood A/C man. You could make some side $$ or just stack up the "favors" for helping some people out.

JCWATERS
Yeah, it should cycle continuously when running. Not super fast but cycling is part of it's normal operation. As for why it's not too cold....? Hard to say without some pressure readings.
I'm going to have to time my cycling today. Not exactly the same truck but I know it works right and cools. The good news is that if it cycles and cools at all the problem can't be too catastrophic.

 

[ford33]

What is cycling? I am guessing it is the compressor turning on then off? My compressor seems to always be engaged when my a/c is on. Is that bad?

 

[rhauf]

Does anyone know what the air pressure is supposed to be on the low a/c port when it's like 100 degrees out? I think I am going to try to recharge again.

it fluctuates as the a/c pump goes on and off.. now i'm not an a/c "expert" but i've built a couple a/c systems, and repaired quite a few, and had pretty good success.... my theory is to charge the a/c system (with the engine running, and a/c on high) until the a/c clutch runs constantly at idle. if it's cycling at idle then there is probably not enough charge in the system. you should be able to rev the engine up to, and hold a steady 1500 rpm or so before it starts cycling.

the low pressure switch (that thing on the side of the accumulator) will shut off the compressor when low-side pressure gets below about 15psi. this is the only indicator of pressure i use. (with a gage, when the switch shuts off at 15psi in an undercharged system, the gage will of course shoot right up to some much higher pressure before it cycles back on)

and if you're fan is an issue, i wouldn't even consider an electric fan. they move far less air than mechanical fans. just be sure the clutch is good (if you turn the fan by hand, with the engine off, you should feel resistance, if it turns easily/keeps spinning, then its bad) also if it's bad you're engine temp would probably rise in low speed driving as the radiator can't cool either. i'll just assume you're fan shroud is in place and has not been removed.

everything gus said also sounds correct