AC Clutch always engaged, blows cool air but not cooling the cabin

Chiper91

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Sep 23, 2018
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98 GT

Recently I noticed that my cabin is not cooling enough even when the AC is on max setting. I checked the low pressure and it showed 35 PSI. I live in the South so the temps are usually around 90 F and pretty humid this time of the year. After searching on the net, I found that it should be closer to 40 50 PSI so I added some Freon until it got to 45 PSI. Still the cabin does not cool down.
At that moment I noticed that the AC clutch is always engaged regardless of whether the AC setting I on normal or max. The clutch disengages when I switch off the AC. I've yet to get an UV flashlight and check for leaks.
After reading online forums I found that the AC clutch cycle switch near the AC dryer could be faulty and thus make my clutch spin without disengaging. Could it also be the CCRM?
The AC compressor was replaced and recharged 7 months ago. The air flow in the cabin seems to get colder/ stronger with WOT. I don't know if that is connected.
Any help would be appreciated.
 
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wmburns

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After reading online forums I found that the AC clutch cycle switch near the AC dryer could be faulty and thus make my clutch spin without disengaging. Could it also be the CCRM?
Not the CCRM. Why? Because the AC clutch is engaging. IF this were a CCRM problem THEN the AC clutch would not engage. Sounds like the CCRM and AC clutch is working just as it should.

Have you confirmed that the radiator cooling fans run?

Is there a good air flow from the inside vents?

It would help to know the high side pressure reading.

Have you looked to see if there are any kinked lines?
 

Chiper91

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The radiator fan is working as per usual. My passenger vent in the cabin is not blowing at all (yes, it is open). I tred closing one of the other vents to see if it redirected any flow. No changes.
Is that somehow connected to the constantly engaged clutch?
Finally, is it okay drive with the AC on? I am afraid I will burn out the compressor if the clutch is engaged all the time.
I will get the gauges tomorrow to measure the high side pressure.
 

wmburns

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My passenger vent in the cabin is not blowing at all (yes, it is open)
Seems to me that THIS is your problem. Possible that some of the duct work behind the dash has become disconnected.

Have you checked to be sure that the AC/heater blend door temperature control is connected and actually moves the blend door when the temperature knob is moved?

IF there's no air flow through the AC coil then it will freeze.

It's not possible to get good pressure readings unless there is enough air flow across both the inside and outside coils.
 
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Chiper91

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Hey,

I just checked the vents and used the temp control to change from cold to hot temp. THe center and driver's side vents changed very quickly. The passenger side vent also changed to hot air but the flow was still weak. There is weak flow for both, cold and hot air from passenger side.
I also checked the low and high pressure. Under full AC load, I get 45 low PSI and 275 Hgh Psi under 85 -87 F and 70% humidity. I think the high pressure is too high.

I also checked the fan. As far as I know it supposed to have two speeds. After changing from no Ac to norm Ac to Max ac, I honestly could not tell the difference in fan speeds. I am really bad at this. But their was pretty hot when I held my hand next to the fan. Is that how it is supposed to be?
I also read online that if my orifice tube is clogged or malfunctioning, then it could cause a constantly engaged clutch. Is that true?

I get colder air in the cabin when I accelerate, is that connected?
 
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wmburns

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At that moment I noticed that the AC clutch is always engaged regardless of whether the AC setting I on normal or max.
The AC mode setting won't have any effect on the AC clutch. Only the low pressure cycling switch would "cause" the AC clutch to cycle on/off.

The AC mode control switch in the MAX affects the source of outside cabin air. In the normal position cabin air is drawn from the outside. In the MAX position the cabin air is drawn from the inside of the cabin (recirculated).

IF the high side pressure is too high THEN:
  • the outside coil is dirty or blocked
  • there's not enough air passing over the coil
  • There's a blockage in the high side lines.
  • the system is over charged.
If you are not hearing any difference in the inside fan speeds then suspect a bad fan ballast resister.

MOTORCRAFT YH1699
https://www.rockauto.com/en/moreinfo.php?pk=1285234&cc=1304480&jsn=467
 

Chiper91

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Sep 23, 2018
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The AC mode setting won't have any effect on the AC clutch. Only the low pressure cycling switch would "cause" the AC clutch to cycle on/off.

The AC mode control switch in the MAX affects the source of outside cabin air. In the normal position cabin air is drawn from the outside. In the MAX position the cabin air is drawn from the inside of the cabin (recirculated).

IF the high side pressure is too high THEN:
  • the outside coil is dirty or blocked
  • there's not enough air passing over the coil
  • There's a blockage in the high side lines.
  • the system is over charged.
If you are not hearing any difference in the inside fan speeds then suspect a bad fan ballast resister.

MOTORCRAFT YH1699
https://www.rockauto.com/en/moreinfo.php?pk=1285234&cc=1304480&jsn=467

I am not sure if the high pressure is too high or not. I looked up a chart online and it said that for my temp it should be 250 PSI at max, and I have 275 PSI.

When you mention the inside and outside coils, what do you mean? I am not very strong with the HVAC system.
I am thinking that I might have a clogged orifice tube but I don't know its location in the 98 GT.
 

90sickfox

I didn't really have an issue with the stink...
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Sounds to me like hou have a mother motor issue. Does the air force ot the vents change when you change the interior vent fan speeds. If theres no force coming out of the vents then you need a blower motor... or blower fan resistor
 

Chiper91

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Sounds to me like hou have a mother motor issue. Does the air force ot the vents change when you change the interior vent fan speeds. If theres no force coming out of the vents then you need a blower motor... or blower fan resistor
The air force changes on the vents that operate properly (central and driver side) but the force does not change on the passenger side. Would the malfunctioning blower motor also explain the constantly engaged AC clutch?
 

wmburns

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If the orifice tube is clogged it can be risky to just replace the orifice tube without flushing the entire system. Because the orifice may quickly clog back up.

FOUR SEASONS 55721
https://www.rockauto.com/en/moreinfo.php?pk=818179&cc=1304480&jsn=476

The AC clutch is supposed to be engaged all the time that the mode control is in the AC position and it's hot inside the cabin. Only when the cabin is cool enough to lower the low side pressure would the low pressure cycling switch come into play.
 
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Chiper91

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I see. I think I replaced the orifice tube when I replaced the AC compressor.
It seems that I should prepare to disassemble the dash to get to the evaporator core. Could anyone suggest any videos or instructions on how to do it?
Or can I somehow fix it without taking the dash apart?
 

wmburns

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I had a 1996 Convertible with a leaking AC evaporator coil. The complete dash needed to be pulled to gain access. I have to be honest here. It was a BIG job. After I did the job myself it was easy to understand why the professionals charge sooooooooooo much.

Lessons learned:
  • remove the front seats
  • pay the $$ for a Chilton repair manual. The pictures and step by step is well worth the price of the manual. Follow it.
  • IF the evaporator coil does need replacing the buy the Ford service replacement. It's not that much more expensive and you will thank me should you buy just the AC evaporator coil. I spent several days trying to separate the plastic outer shell before paying the extra $$ for the Ford service replacement. Money well spent.
  • One man can do the whole job until it gets time to lift the dash out. Will need a buddy then.
  • There are surprising few things that actually hold a dash into a modern car.
  • Once the dash is out this is your chance to check all of the vacuum damper motors and AC blend door.
When the dash is out inspect the firewall where the drain goes through. Look for creased metal that may be pushing on the plastic of the AC case.

I'm sure it would help the Mustang community if you were to document the process with your own "lessons learned".
 

Chiper91

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Sep 23, 2018
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I had a 1996 Convertible with a leaking AC evaporator coil. The complete dash needed to be pulled to gain access. I have to be honest here. It was a BIG job. After I did the job myself it was easy to understand why the professionals charge sooooooooooo much.

Lessons learned:
  • remove the front seats
  • pay the $$ for a Chilton repair manual. The pictures and step by step is well worth the price of the manual. Follow it.
  • IF the evaporator coil does need replacing the buy the Ford service replacement. It's not that much more expensive and you will thank me should you buy just the AC evaporator coil. I spent several days trying to separate the plastic outer shell before paying the extra $$ for the Ford service replacement. Money well spent.
  • One man can do the whole job until it gets time to lift the dash out. Will need a buddy then.
  • There are surprising few things that actually hold a dash into a modern car.
  • Once the dash is out this is your chance to check all of the vacuum damper motors and AC blend door.
When the dash is out inspect the firewall where the drain goes through. Look for creased metal that may be pushing on the plastic of the AC case.

I'm sure it would help the Mustang community if you were to document the process with your own "lessons learned".

I ordered the Chilton manual and scheduled a Saturday to work on this. Do you think it is possible to do everything in one day if you start in the morning?

Also, I cannot find any place where they would sell the AC blender doors. Could you pinpoint an online parts retailer? Rock auto does not seem to have them.

Finally, when I turn the key but don't start the car, and the AC is on, I can hear some chirping sounds coming from the dash? Are those the AC blender doors? The sound is similar to the one you would hear if tree branches are scratching your car while driving through a forest. That's the closest I can describe the sound.
After draining the overcharged refrigerent, my high pressure side is too high. Should I look into the condenser, fan?
 

wmburns

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Should I look into the condenser, fan?
As I said before, it's not possible to accurately access AC performance unless the air flow across the inside and outside coils is adequate. Anything that restricts air flow such as dirt or out of place air dams are all possible causes. The fans must work on BOTH speeds and the coils need to be clean.
Do you think it is possible to do everything in one day if you start in the morning?
It took me the weekend to remove the dash. I worked the worked the work week to get the evaporator coil in place and the dash ready to re-install. Then another weekend to re-install the dash. Could I do the job quicker next time? Certainly.
I cannot find any place where they would sell the AC blender doors.
What I have done is to get parts from a salvage yard. I wouldn't have a problem getting an entire salvage yard dash in order to have what ever part is needed to finish the job. Try searching car-part.com to see some sample prices and availability.
The sound is similar to the one you would hear if tree branches are scratching your car while driving through a forest.
All I can say is once the dash is out it will be much easier to trouble shoot any vacuum leaks. Use a hand vacuum pump to exercise the damper motors. Make sure the linkage moves free. Take tons of pictures before taking anything apart.
 

Chiper91

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Sep 23, 2018
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As I said before, it's not possible to accurately access AC performance unless the air flow across the inside and outside coils is adequate. Anything that restricts air flow such as dirt or out of place air dams are all possible causes. The fans must work on BOTH speeds and the coils need to be clean.

It took me the weekend to remove the dash. I worked the worked the work week to get the evaporator coil in place and the dash ready to re-install. Then another weekend to re-install the dash. Could I do the job quicker next time? Certainly.

What I have done is to get parts from a salvage yard. I wouldn't have a problem getting an entire salvage yard dash in order to have what ever part is needed to finish the job. Try searching car-part.com to see some sample prices and availability.

All I can say is once the dash is out it will be much easier to trouble shoot any vacuum leaks. Use a hand vacuum pump to exercise the damper motors. Make sure the linkage moves free. Take tons of pictures before taking anything apart.


Hey. I am goin to work on the dash next week. I already ordered the repair manual and found the blender doors from a GT that is being parted out.

This morning I went to an AC shop. A couple of days ago I drained some refrigerant and the AC clutch started to cycle on and off. I got to the shop and decided to do a full vacuum and recharge. It turns out I had less than half of the adequate amount of refrigerant amount. We recharged the AC system, no leaks. My pressure was 35 PSI low and 275 PSI high. The mechanic said it is normal given the temp and humidity. THe AC blew cold and the temp next to vent was around 35 F. The car was in the garage.

When I got back and parked my car outside my pressure was 28 PSI low and 225 high. Compressor clutch always engaged. On max cold AC, my temp in the vent was 58 F. I used the thermometer from the AutoZone (the one with the thin thing that goes inside the vent; the mechanic used an infrared thermometer).
The mechanic told me that it is okay for the clutch to be always engaged given the outside temp and that the low pressure is pretty high, the clutch usually engages only if the low side get lower than 20 PSI. Basically he said that my AC system works fine.

As for the sound from the dash and weaker flow from the passenger side, the sound may indeed indicate failing blender doors. The weaker flow is characteristic for SN95. He showed me a New Edge with a new evap core and reconnect ducts. Same thing, the passenger side was weaker than the center and driver side vents.
Given the above, is my AC system okay or not?
 

wmburns

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The sound is similar to the one you would hear if tree branches are scratching your car while driving through a forest.
If this were my car I would look for debris such as tree leaves falling into the inside cooling fan via the passenger's intake cowl vent. This might also explain where the air flow blockage might be.

Of course one can't rule out the possibility of rodent activity. It wouldn't be the first time un-welcomed guests have made a home in the cabin fresh air box.

I can't possibly tell you if your AC is OK or not. But the simple answer to the question might be, "is the cabin getting cool or not?". Since it's not keeping you cool, then the answer is no. But maybe it's a good idea to remove the inside cooling fan cage and lay eyeballs on it before undertaking a complete dash removal. This will also give a good chance to inspect the blower resister. They usually rust out from moisture.

It couldn't hurt to clean under the cowl vent as well.
 
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