A/C Question Please.

Today, I noticed that the A/C clutch always engaged. Won't release. I remember that usually the clutch should engage for about 1 minute then release for a while and then engage for about 1 minute. Is there any problem if the clutch always engage? Is there anything wrong? The air is still cold but I feel that before was a little bit colder, maybe just because fo the hot weather.

The clutch will always be engaged while the cabin thermostat is calling for cold air. Either the outside temperature is higher or your A/C is low on refrigerant. You could have the shop check the A/C system, they can tell you if you need a recharge by comparing refrigerant operating pressures to corresponding system temperatures. Alternativly, you can wait a little while ... if refrigerant is low enough to reduce A/C output, it won't be long before there is NO cold air output. At that point you could add 16oz of refrigerant yourself.

If you have a shop service the system, my guess is that they will just add a can of refrigerant.

Thank you. You mean, it because of low refrigerant? Last year, before summer, there is NO cold air output. the sympton is that the clutch did not engage at all. I added less than two cans of refrigerant and made the pressure in right range. It works very well more than a year. This afternoon I checked the pressure, it's still in the full range. Actually, I worry about the relay or something alse. I do not know about the A/C system.

Your A/C may have developed a slow leak ... the 2 cans you added last year may be gone. The problem with trying to measure the refrigerant level by looking at the system pressure is ... the pressure stays constant (for a given temperature) until the refrigerant level falls below the critical operating weight. It's like a sealed container of water on a stove with a little hole in the top ... the container pressure will stay the same until all the water boils away, then the pressure drops suddenly.

I wouldn't worry about the A/C clutch or relay. My guess is still with refrigerant although if the system gets cold and then quits for a while, there may be moisture in the system.

Got it. Thank you. I will wait untill no cold air.

Well, the clutch won't stay constantly engaged due to low refrigerant, which is what the original post is asking about. If the system pressure drops, or exceeds a threshhold, the clutch will disengage, but neither of these conditions will cause an otherwise properly working system to keep the clutch engaged.

I'd suspect that the issue here is either one of the pressure sensors has been bypassed, or the system is working fine and the cabin temperature is calling for continuous dehumidification.

-Rod

Well, the clutch won't stay constantly engaged due to low refrigerant, which is what the original post is asking about. If the system pressure drops, or exceeds a threshhold, the clutch will disengage, but neither of these conditions will cause an otherwise properly working system to keep the clutch engaged.

I'd suspect that the issue here is either one of the pressure sensors has been bypassed, or the system is working fine and the cabin temperature is calling for continuous dehumidification.

-Rod

This is my answer. I just want to know which sensor or sensors? Thanks.

When your air conditioner control switch is set to maximum, the clutch will remain engaged, provided your system is working properly. If you set it to normal, the clutch will kick in and out. Low freon will not cause the clutch to remain engaged, quite the opposite.

Ron

But I remember when I added refrigerant last. I setup the switch and fan speed at maximum. Before I added the refrigerant, the clutch never engaged. When I started to add the refrigerant, the clutch engaged longer and longer untill to about 60 seconds (someone told me, 60 senconds engagement is good). The pressure gauge did help, once the clutch started to engage. the pressure was in the full charge range. When the clutch quit engagemnet, the pressure will drop fast and come back again when the clutch was engaged. So I have to count the engagement time.

On a hot day 85 to 90 degrees or more. If your Air conditioner is set to maximum and your refridgerant is at the proper level it probably will not dis-engage at all.

The best way to add freon is with proper guages, not with timing or any other methods. Proper internal presures are critical to the air conditioner's performance. If your presure fell when the clutch disengaged them you have the guage hooked up to the high presure side. I hope you weren't some how adding freon to the high presure side! Very dangerous!

At any rate your low side should run about 30 or so pounds and the high side around 200 lbs.

Ron

What kind of guages are proper?
I used this.
http://www.id-usa.com/product.asp?CID=27&PID=45

The sensor that controls the A/C is the "Clutch Cycling Pressure Switch" mounted on the condensor which is located on the firewall. This switch is located (electrically) between the cabin thermostat and magnetic clutch ... it opens at 25 psi and closes at 45 psi. Under normal operating conditions it will supply the clutch with +12 volts anytime the cabin temperature control calls for cooling. As the refrigerant leaks out, the condensor pressure (low pressure side of system) will drop below 25 psi and the switch will turn off untill pressure equalizes in the system and the condensor pressure rises above 45 psi (this cycle is repeats itself) ... at this point, the system produces little or no cooling.

Hmmmm . . . It's been 95 to 100F here with 110F heat index EXTREMELY HIGH humidity and set wide open my AC compressor turns off and on and if it didn't it would freeze up. Never had any problem with the AC or had it service or the freon checked, 03 Vulcan 53,500 Mi. I leave it on about 3/4 fan speed and it gets so cold you could hang meat in there. I take my pet with me to work doing house calls and I let it idle with A/C on and it never shows the first sign of overheating or balks about extended idling and it gets cold inside idling. Get on the road moving air through the radiator and can't tell any difference in cooling when it's idling. The wife has an 05 Gran Marquis and it's the same with an excellent A/C system.

Judging from the way our A/C's cool and what I'm reading here I'd say we have exceptionally good AC's in our Fords. My :2cents:

Shut off the vehicle and see if there is an air gap between the clutch hub and the clutch face. There should be between .019 inch and .025 inch gap. If the air gap is gone, it can cause constant engagement. You can alos open hood and work throttle by hand. Run it up to approximately 2000 rpm and the compressor should disengage and engage. Here are the proper gauges to use. (http://www.tooltopia.com/index.asp?PageAction=VIEWCATS&Category=1988&utm_source=OVR&utm_campaign=air%5Fconditioning&utm_content=Bottom%2Bline%2Bpriced%2Ba%2Fc%2B%2A%2 A%2A&utm_term=ac%2Bgauge&utm_medium=PPC&OVRAW=ac%20gauges&OVKEY=ac%20gauge&OVMTC=standard&OVADID=839975021&OVKWID=5016653021&ysmwa=ETEbkQ-P1TAtNUyxOt7z57l1EAscavuQN4YT7URqNiQCchxVuGlA_4VF1 xtNSDjD)

From reading the posts it seems that the opinion here is that the internal (closed pressured refrigerant) system somehow senses cabin temperature and/or humidity and cycles the clutch. The clutch only cycles in response to the external thermostatic cabin control and (in some models) the cabin humidity sensor. The pressurized inside of the of the system is oblivious to outside conditions and the only sensor on the closed system affecting the clutch is the switch on the condensor that turns off the clutch if the refrigerant level is low.

Gary sez, "From reading the posts it seems that the opinion here is that the internal (closed pressured refrigerant) system somehow senses cabin temperature and/or humidity and cycles the clutch." When you have your AC checked they take a thermometer and stick in the vent and best I recall it should be putting out cold air near 40F. Now, as for the cabin temprature sensor, it would probably be near the cooling coils aso known as the 'evaporator' and when it reaches a certain temp it shuts off the compressor. If it didn't the evaporator coils would freeze up and zilch cooling. Thus, take a AC with insufficent freon and the compressor would run longer and as the freon level (pressure) diminished the compressor would run longer because the inside sensor was not happy and called for more cooling

"The clutch only cycles in response to the external thermostatic cabin control and (in some models) the cabin humidity sensor." Hmmmm . . . I'll have to give that some thought. By external I assume you mean the prevailing outside ambient surrounding enviroment. As far as ambient humidity OR temprature is concerned, the AC knows nothing about ambient enviroment and works strictly from temprature readings the sensor takes INSIDE the cabin at OR NEAR the evaporator coils, or it may be in the duct work that carrys cool air to the cabin. The temp setting on the dash, digital or analog, sets the temp INSIDE the cabin which has been the case since way back when vehicle AC's first hit the market before computer circuit boards existed.

Here's the way I see it: If it worked as you say we would have no need of an inside temp control because the external sensor would be overriding the temp we set inside according to the external ambient temprature and humidity. Seems it would take a computer program to read the temp we select, (which, by the way, has nothing to do with humidity), then read the ambient factors then compute what cooling we need inside. Maybe I'm all wrong and later I'm calling the AC shop and ask them and if I'm wrong I'll eat a double helping of Crow. I will grant you, a Mercedes 'prolly has a much more sophisticated AC system than our humble Tauri, but basically I believe they all work the same.

Good discussion and learning thread here and thanks for putting my old brain in overdrive at this early hour. :feedback:

I think I'm being missinterperated ... let me try again.
There is only one control line that operates the clutch ... all temperature, humidity and refrigerant pressure controls are placed in series along this +12 volt control line. What I am trying to say (not very well), is that the clutch only responds to the control line ... there is no reason to suspect the clutch is cycling (if it is) for some reason other than in response to the cabin temp/humidity controls or low refrigerant level.


By external, I mean external to the pressurized refrigerant system.
I think we may be saying the same thing in different ways.:grinyes: