A/C blows hot then cold


RALPHIE

GT Owner
Mar 1, 2007
7,278
thank you Gerry. Mods, can you make this post a sticky?

Agreed! :thumbsup
 

Shelby#18

GTX1 Owner/Moderator
Mark IV Lifetime
Le Mans 2010 Supporter
Dec 15, 2006
1,623
Nev./So. Cal./Minn.
thank you Gerry. Mods, can you make this post a sticky?

Done.
 

soroush

Ford Gt Owner
Mark II Lifetime
Aug 8, 2007
5,256
I don't know if is the same thing but my 65K mile blue car was suffering from an AC problem for the last two years, I was just too lazy to really look into it I guess, the Ac blew cold every time the car was started in the morning and would work fine until the temps got up to 200 then it would quit blowing cold air. then it wouldn't work for the rest of that day, the next day same thing.

well I got off my lazy butt this sat morning ran a test wire to inside the car to make sure in fact the compressor was still getting power when the ac started acting up and blowing hot air, and found that to be the case. I took the pulley off the compressor and replaced the electromagnet thats under the pulley a 35 dollar part! now it all seems to be working great!! over the years I talked to so many people regarding this issue we even changed all the pressure switches and the dryer and expansion valve and all along was the magnet. any way just thought this might be useful, btw I did everything while the compressor was still on the car, so I didn't even have to take the lines off so no recharging the system, sometimes you get lucky!
 

2112

Blue/white 06'
Mark II Lifetime
That is great! By chance to you have a picture of the Magnet or where it is on the compressor? I assume you had to pull the belt and pulley to get to it?
 

soroush

Ford Gt Owner
Mark II Lifetime
Aug 8, 2007
5,256
That is great! By chance to you have a picture of the Magnet or where it is on the compressor? I assume you had to pull the belt and pulley to get to it?

I didn't take any pics but I had the compressor off of my "garage table" ;) in anticipation of replacing it with the one in the car, I can take some pics of that later and post. but basically there is a 13mm nut in the front of the pulley that needs to be removed then the "flywheel" part of the pulley comes out behind it there is a C clip that has to be removed in order for the actual pulley to come out, it takes some elbow grease to get the pulley off especially with the compressor still on the car and all not having the best access, but after the pulley comes out the electro magnet is behind it or rather the pulley is around the magnet but slides off a bearing, then there is a second C clip that needs to be removed and the electromagnet come off, the magnet comes from ford with all the wiring and plug plus the limiter built in all one unit, I really think I paid no more than 35 bucks but that one a year ago.
 

2112

Blue/white 06'
Mark II Lifetime
Any chance you have the part # for the magnet assembly? I can afford to put that part on the shelf just in case. :wink
 

jcthorne

GT Owner
Aug 30, 2011
792
Houston
Poor A/C performance in Hot Weather may be due to the A/C high pressure cut-off switch being set too low. When the high side pressure gets above about 425 psi, it will cut out and not cut back in until 200 psi. You would need to change the switch on the compressor. 4 pin connector, black casing is stock. Scharader valve on it so you don't have to discharge the system to replace it. There is also a pressure relief valve (Dump) that dumps freon if pressure gets too high, usually around 550-650 psi.

Here are the specs:
Black casing switch - YF1Z-19D594-AA - Cooling fan ON - 310 to 340 psi; Clutch cut-out 435 to 475 psi, clutch re-engages at 220 to 280 psi.
white casing switch 8L8Z-19D594-A - cooling fan ON 285-315 clutch cut out 435-475 clutch re-engage 220-280
gray casing switch 7S4Z-19D594-AA cooling fan ON 227-257 clutch cut out 420-460 clutch re-engage 220-280

If you go with the white casing switch, you can get the high speed cooling fan on sooner. I could not find a 4 pin switch with a higher cut-out pressure.
You can verify it is cutting out due to high pressure by hooking up a set of a/c gauges and watch as pressure rises on the high side gauge, and watch when the compressor clutch kicks off. If you hook up a jumper with switch to the 2 pins for the cooling fan, you can control high speed fan to go on when you flip the switch.
When I forced the high speed fan on myself, the high side pressure dropped immediately and the a/c clutch stayed engaged. I did this on my Mercury with similar sysytem. I think we delayed the high fan so we could pass the alternator charging system performance test. My preference is to have the fan come on around 200 psi. My Mercury switch is 4 pin, very similar, and the obsolete switch I installed turns the fan on much sooner. Not sure if it will physically fit the GT, but the switching is the same. Cut-out switch is normally closed, the cooling fan swithch is normally open. I can provide that switch part number and a source if anyone wants to try it. About $45. Gray casing.

Gerry from Ford Service Engineering



I would be interested in the part number and source for your grey body switch with the lower fan cut in pressure. I'd like to look into it and see if it will fit and if it helps the ac in high temp conditions.

I ran into this yesterday during a spirited drive in the texas hill country. Temps were 108 to 110 so yes it was hot and yes I was not limping along but if bringing the high speed fan on sooner could help, I'm willing to do some leg work to try. I also plan to lower the high speed fan set point on my engine temps by a few deg. its currently set at 215 and that is where the needle sat, the engine never go hotter and you could hear the high speed fan cutting on and off. Eventually dialed back my driving, dropped the car in 6th for a while and the engine temps dropped to 190 and the ac never cut out again.
 

KJRGT

GT Owner
Mark II Lifetime
May 4, 2006
2,840
SoCal
My AC was taking a little longer to get cold so today I gave it a re charge. Even though the pressure was reading fine, it took some refrigerant and immediately the air was much colder.

Might be worth it to give your GT a hit of 134A even if it's performance seems OK. After ten years and 23,500 miles it gave my system nice little jolt.
 
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Gerry

Well-known member
Oct 13, 2006
51
Dearborn, Michigan
You might want to try a revised a/c high pressure cut out switch. 8C3Z-19D594-AA.
It has the same fan "ON" specs, but the fan doesn't cut out until pressure drops to 225 psi on the high side line, while the old switch fan cutout is 275 psi. The revised switch should keep the fan on longer which will reject more heat from the condenser.

This same newer switch delays cutting out the compressor by 15 psi, which should keep the compressor on a little longer.

When the cutout switch is active, you get warm, humid air coming out the vents until the compressor kicks back in.

Gerry from Ford
 

Triheart7

GT Owner
Mark IV Lifetime
Apr 3, 2007
2,576
Northern California
Interesting post. When I drove from Sacramento to Monterey two weeks ago it was a 100 when I left and after about 20 min of driving the AC cut out and I drove down the Central Valley for three hours of painfully hot driving. I previously joked I tried to roast Gabrielle.

When I came back , my Ford dealer tested everything and everything is working fine. I did accelerate "rapidly" before it stopped cooling so possibly that affected my system.

Anyway thanks for the post, if my system does this again I'll have to re-read the post again and maybe I can show it to my technician!
 

STORMCAT

GT
Mark IV Lifetime
Le Mans 2010 Supporter
May 25, 2006
7,554
Ft. Lauderdale
This is an old post and I haven't read through everything. Had an issue with my compressor cycling on and off and or not engaging at all. Turned out just to be the AC compressor relay located under the front trunk.