Air conditioning help

[TomCat]

About two weeks ago, due to intermittant ac, I took my car to a shop. My independent mechanic suspected a sticking expansion valve and said I should get a second/expert opinion. Acura said same thing...$1200 to fix (removing dash).

I did the expansion valve through the fire wall method and refilled with 134a.
It blew cool for a little while then stopped and then blew cold again (much like a sticking expansion valve???).

I have noticed that the tube (circled below) is extremely cold when the ac is NOT blowing cold and the tube warms up when the system seems to be working fine. ???

Also while diagnosing this issue, I heard what sounded like a hose blow and hissing (with some associated mist (not really smoke) and dust...like a ac hose blew...but I could not trace it (might have even come from the engine compartment, and after I shut down and re-started, the ac blew cool??? Is there some sort of over-pressure relief valve that may have popped an reset once over pressure was reduced?

But ac remains intermitant and the sight glass on top of the dryer seems to indicate air in the system??? I have tried to continue to fill with 134a...but it should be overfilled by now.

Thanks

 

[TomCat]

Additionally, at least right now, while idling in my garage (at 90F ambient) the compressor cycles on for about a secod every 8 seconds.

 

[Briank]

You did evac the air out of the system?

 

[TomCat]

You did evac the air out of the system?

How...upper high pressure port?

 

[Briank]

The proper method is to use a vacuum pump to pull vacuum on the system and then fill with a measured by weight amount of Freon. Since your system was open it could have moisture in it (ice crystals), too much Freon and you have a high pressure issue, to little and you have a low pressure issue both will be sensed by the triple pressure switch and shut down the compressor. Also having air in the system messes up the pressures. I would dump most of the charge and the refill a couple of times and that should get rid of most of the air and water.

 

[TomCat]

The proper method is to use a vacuum pump to pull vacuum on the system and then fill with a measured by weight amount of Freon. Since your system was open it could have moisture in it (ice crystals), too much Freon and you have a high pressure issue, to little and you have a low pressure issue both will be sensed by the triple pressure switch and shut down the compressor. Also having air in the system messes up the pressures. I would dump most of the charge and the refill a couple of times and that should get rid of most of the air and water.

Thanks, I'm having professionally serviced tomorrow.
Do you know of an over pressure valve that mght have released...causing the pop/hiss? The system seems to work (albiet intermittantly) after this episode?

 

[Briank]

Thanks, I'm having professionally serviced tomorrow.
Do you know of an over pressure valve that mght have released...causing the pop/hiss? The system seems to work (albiet intermittantly) after this episode?

No over pressure that I know of, some times when my compressor kicks out it is kind of a pop and a hiss noise.

 

[TomCat]

Looks like the "reed valve" in the compressor is bad.
Does that mean I need to replace the whole compressor?
If so, source and expected $s?

 

[nsx20014me]

The proper method is to use a vacuum pump to pull vacuum on the system

Sorry for the hijack. Can you summarize how to do this. Do you hook up the vacuum pump on the low or high pressure side? And do you have the engine running with the AC on?
TIA
Tom

 

[TomCat]

Can somebody check (while their ac is on max cooling) the temperature of the tube circled below?
I'm expecting either warm/ambient or cold.

 

[Briank]

Sorry for the hijack. Can you summarize how to do this. Do you hook up the vacuum pump on the low or high pressure side? And do you have the engine running with the AC on?
TIA
Tom

The compressor will not run with little or no pressure in the system so running the car is unnecessary. I would say the low pressure side would be the place to connect but I can't say for sure.

 

[Briank]

Can somebody check (while their ac is on max cooling) the temperature of the tube circled below?
I'm expecting either warm/ambient or cold.

That is the high side so it should be something other then cold.

 

[TomCat]

That is the high side so it should be something other then cold.

As I suspected...(I took thermodynamics in college-TWICE)
Usually, just after initial start, the ac blows pretty cold and THAT tube is ambient or slightly warmer...when the ac stops blowing cold, that tube is COLD!

So, in which direction is the flow and where is the cold coming from (on the high side

 

[Kitaka]

A certified A/C tech will be able to diagnose your operational problem instead of charging you for unnecessary work and parts, and releasing unwanted refrigerant to the environment. I'm unimpressed that the repair person did not check the work after completing repairs. What a rip-off!

It sounds like your TXV expanson valve is flooding, causing it to freeze up, Excessive moisture would also contribute to the problem. Get the book Automotive Air Conditioning (Boyce H. Dwiggins) from your local library. It describes your problem and the causes/fix. It's lengthy reading but the knowledge you'll gain is priceless. The refridge cycle is very basic and once you understand the basic automotive application, with a few tools, you'll wonder why you took the car to someone else instaed of doing it yourself. I made a few extra $$$ repairing TXV systems after reading information that ASE techs use to train/certify with. I've had no opportunity to work on FOT systems yet.

 

[Briank]

As I suspected...(I took thermodynamics in college-TWICE)
Usually, just after initial start, the ac blows pretty cold and THAT tube is ambient or slightly warmer...when the ac stops blowing cold, that tube is COLD!

So, in which direction is the flow and where is the cold coming from (on the high side

When the compressor shuts down and the pressure goes away the liquid changes back to a gas and get cold.

 

[TomCat]

When the compressor shuts down and the pressure goes away the liquid changes back to a gas and get cold.

I got some gauges...and I don't know if I confirmed the compressor continued to operate...
Now I have things to check.

 

[TomCat]

I'm unimpressed that the repair person did not check the work after completing repairs. What a rip-off!

Get the book Automotive Air Conditioning (Boyce H. Dwiggins) from your local library. It describes your problem and the causes/fix. It's lengthy reading but the knowledge you'll gain is priceless. .

I did the expansion valve repair myself...and maybe it didn't go right?

Great idea on the book!
Thanks

I have some more trouble shooting to do.
Tom

 

[SOURCE 1]

You need to get it on a machine, Properly evacuate the system ( not only recovers the refrigerant but cleans out the lines etc ) this will verify you are starting with a clear system. Recharge it while adding some dye in case you have a leak somewhere. It will probably work correctly. And if it does not anyone who knows a/c systems would be able to tell you what the issue might be. A/c is not rocket science but when pressures are wrong it will do all kinds of weird stuff. AND when the system is opened and not vacuumed it will drop pressures causing issues such as yours.

We charge $99.00 for an a/c evac and recharge with dye just so you have a starting point when you go to price it.

 

[TomCat]

You need to get it on a machine, Properly evacuate the system ( not only recovers the refrigerant but cleans out the lines etc ) this will verify you are starting with a clear system. Recharge it while adding some dye in case you have a leak somewhere. It will probably work correctly. And if it does not anyone who knows a/c systems would be able to tell you what the issue might be. A/c is not rocket science but when pressures are wrong it will do all kinds of weird stuff. AND when the system is opened and not vacuumed it will drop pressures causing issues such as yours.

We charge $99.00 for an a/c evac and recharge with dye just so you have a starting point when you go to price it.

This is where I am at...my independent evacuated and re-filled to 134a specs.
He thinks the compressor has sticky reed valves since (I believe he said) he was not getting pressure on the high side.

That being said, it may be intermittant problem since (for a few minutes) it
seems to work okay. I am concerned that when it IS working (blowing cold air into the cockpit) the tube associated with the high pressure port is ~ambient temp (or warmer) and when it is not working the tube for high pressure port is COLD.

 

[ralph cerbone]

Indication of bad reed valve will be a bouncing of high pressure gauge . He should recognize this immediately . Also dependent on how bad the seal is will effect the low pressure . The high side of an AC system has to be hot ( above ambient),low side will be cold (sweating).Anytime the high side is cold or icing is indication of a restriction or severe under charge. These are basic guidelines , if you have pressure readings would help, I can tell you how to diagnose a leaking valve but you will need gauges and a vacuum pump. Very few a/c techs have even done these tests.

 

[LJSB]

I'm sorry if I missed it but what year is this vehicle?

 

[McFridgeGuy]

Bad valves on your compressor would lead to extremely hot temperatures on the discharge line (going from the compressor to the condenser), and a higher than usual suction line (evaporator to the compressor) and a lower than usual discharge line.

The line you have circled above is the liquid line. During normal operations the liquid should be warm. If it's cold you have liquid leaking back somewhere.

If you're AC system has a history of not properly being evacuated (vacuumed) there will most likely be a build up of sludge somewhere in your system (refrigerant + moisture = sludge/wax/acid). That would require you to change out your dryer.

Get me some pressures and I'll pinpoint your issue.

 

[TomCat]

Indication of bad reed valve will be a bouncing of high pressure gauge . He should recognize this immediately . Also dependent on how bad the seal is will effect the low pressure . The high side of an AC system has to be hot ( above ambient),low side will be cold (sweating).Anytime the high side is cold or icing is indication of a restriction or severe under charge. These are basic guidelines , if you have pressure readings would help, I can tell you how to diagnose a leaking valve but you will need gauges and a vacuum pump. Very few a/c techs have even done these tests.

As I suspected...high pressure, higher temp...low press. lower temps.

 

[TomCat]

I'm sorry if I missed it but what year is this vehicle?

1991 but converted by an independent to 134a

 

[TomCat]

Bad valves on your compressor would lead to extremely hot temperatures on the discharge line (going from the compressor to the condenser), and a higher than usual suction line (evaporator to the compressor) and a lower than usual discharge line.

The line you have circled above is the liquid line. During normal operations the liquid should be warm. If it's cold you have liquid leaking back somewhere.

If you're AC system has a history of not properly being evacuated (vacuumed) there will most likely be a build up of sludge somewhere in your system (refrigerant + moisture = sludge/wax/acid). That would require you to change out your dryer.

Get me some pressures and I'll pinpoint your issue.

Thanks...I'll try to get some pressures...
I'm leaning towards dryer too as the possible culprit.