AC Help

[airemdwn]

My compressor is rapidly turning on and off.
Few weeks ago I was driving with the defroster on and it was working fine for 15 minutes then i heard it cycling so i shut it off, waited a minute or so, turned it back off and it didnt do it again. Used it a few times since and it did the same thing works for 10 minutes or so then cycles, i leave it off for a minute turn it back on and its fine?
Static pressure is about 60psi and its cold here about 45* today when i checked it so im not really sure at these temps what its supposed to be near?
Low side does drop to about 25 when it drops the compressor out High side reaches 120. Compressor comes back on at 48 but cycles unless i turn it off then back on?? i changed the pressure switch but its still the same. I converted to 134a in spring with all new parts except the evap. it was fine all summer and evything sounds good. Is it just low and develop a leak? why does it stay on sometime?

 

[Big Ray]

did you use a 134 pressure switch...?

 

[Big Ray]

this may help...

 

[British Slave]

The pressure dropping to 28# tells me you are low on refridgerant.

 

[Fordum]

Good possibility there is nothing wrong. That low pressure switch is on there for more reasons than low refrigerant.
When its cold, the low side pressures drop. If there is not enough heat in the air to completely boil the liquid, it can get back to the compressor and destroy it.

Your metering system can only do so much. Older systems that used expansion valves could completely shut off the flow until it all boiled.
Orifices meter the flow, but cannot stop it. With cool outside temps, the radiator gets too efficient and cools the gas off too much.
This drops the overall pressure and causes the liquid to enter the system cooler than normal.

Then the inside air is cool, and there is not enough heat in the system for it to work.
This will cause the evaporator to freeze up, plus let liquid get back to the compressor.
The low pressure switch turns off the compressor until it all boils and the pressure rises.

It still could be low on gas, but since it works sometimes, I suspect its just the cold weather.
Sitting still lets the engine heat from the radiator get into the condenser plus the compressor is not pumping that fast.
When you start going, the condenser gets cooler and the compressor pumps faster.

I have a couple of ice machines I keep going that are in unheated areas. One of them at my hunting camp.
When the outside temp gets below about 45, they would quit working.
The compressor compresses the gas and builds up the pressure. Then the condenser converts it from high pressure hot gas to lower, but still high, warm liquid.

When the air temp gets too cold, the high side pressure drops so low, that the condenser just fills up with cool liquid and there is not enough pressure to push it through the system.
The compressor does not have enough gas coming in to push the refrigerant on through.

So, I put a high pressure switch on the fan. Now the fan does not come on until the output of the condenser hits 150#.
On warm days, it kicks on after a few seconds and stays on. On cool days, it takes a while to come on, then cycles on and off maintaining the high side pressure.

That way the ice machines will work right on down until the water going to them freezes.

I have another switch for that...........

 

[airemdwn]

Yes im using four seasons pressure switch 36675 for 134a. i put dye in the system when i originally charged it but i dont see anything under the blacklight unless its the evaporator.
Every chart i see doesnt go low enough for this beautiful winter weather and it doesnt fit in my garage to warm it up. i hate to overcharge it if its just a switch or something else making it short cycle.

 

[Fordum]

Like I say, if its a temp thing, then its normal. I certainly would not add any gas until it quits or you find a leak.

I never have totally understood why they went from expansion valves to orifices. Cost maybe.
Properly setup, an expansion valve gives much better control of liquid and temperature.

 

[airemdwn]

Thanks,, im going to double check the pressures and get some heat on the condensor and check the evaporator tonight,which is going to be a huge PITA. But its the only thing i didnt change and cant see 100% to check with the blacklight.

 

[blazer74]

More than likely colder outside temps like Fordum says. If its colder than a well diggers lower end it wont come on at all or cycle constantly.
If you have a leak oil should be coming out somewhere.
Usually those pressure switches are adjustable, I still have the r12 switch and adjusted it.

 

[British Slave]

Put a jumper in the switch plug and see what happens. But remember that low pressure switch is there to protect the compressor so don't run it very long.

 

[82355]

Like I say, if its a temp thing, then its normal. I certainly would not add any gas until it quits or you find a leak.

I never have totally understood why they went from expansion valves to orifices. Cost maybe.
Properly setup, an expansion valve gives much better control of liquid and temperature.

Look at an expansion valve, then look at an orifice tube. I am pretty confident cost was the deciding factor.

Martin