A/C freezes over on long drive - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

itsjustdaphne · 04-05-2015, 06:39 AM

I have an S15 SR swapped zenki with working A/C, and after a 45 minute drive or so the A/C freezes over and on speed 4 it feels like no air is coming out at all out of the dash vents. I'm certain that the drain tube is unclogged because when I park there's always water on the floor, but after driving for an hour I can pick up little icicles off of the blower unit behind the glove box. I tried keeping the A/C button off and going to full heat and it still does it (no heater lines hooked up), so the only fix is to keep the A/C off for 15 minutes and turn back it on.

blkvrtswp · 04-05-2015, 07:34 AM

AC can do this if the system has too much Freon (or whatever replacement gas is in there). Sometimes too little gas can also do the same thing. Drop into a shop that offers $30 AC check / recharge, they can quickly hook up the gauges and see what is going on with the gas pressures.

Other causes would be due to airflow - is the AC condenser/radiator too blocked by FMIC, cooling fans, oil cooler perhaps? Are you using the under engine shroud? Do you have a radiator fan shroud?

Also, if the compressor just runs with no cycling this can easily happen. Check to see if you can hear it click loudly on and off while running the AC.

Good luck - my next year's project is getting AC to work in my swapped 'vert!

itsjustdaphne · 04-05-2015, 10:32 AM

I do have a FMIC, but I have flex-a-lite cooling fans on high mode when the A/C kicks on. AndIi do hear the compressor cycle on and off randomly as the A/C is turned on.

itsjustdaphne · 04-07-2015, 12:42 AM

Did some more poking around at this issue after my powersteering line exploded. -_-
So we hooked up some gauges to it and the numbers are awesome. Butttt it appears the compressor doesnt know how to cycle off when needed...

dbeiler · 04-07-2015, 09:39 AM

How is your AC wired up since the engine swap?

In a functional, stock setup, there are two things responsible for cycling the compressor. The first is the Triple Pressure Switch mounted on the AC drier. This switch will shut off the compressor when the pressure becomes too high or low. The second is the Thermo Control Amplifier mounted on the evaporator casing under the dash. The thermo amp monitors the evaporator temperature and will shut off the compressor when the temp approaches freezing.

I've been doing some research on wiring the AC for my RB s14. I was very disappointed to discover most people will simply splice some wires at the M63 plug (passenger footwell chassis interface plug). This method effectively bypasses the Thermo Control Amp and the compressor cycles off the Triple Pressure Switch alone. With the thermo amp bypassed, the compressor will keep running and freeze up the evaporator. A few people have gotten past this by slightly overpressurizing the AC Freon. The higher pressure in the lines will activate the pressure switch earlier and more often, thus allowing longer 'break periods' for the condenser, keeping it from freezing over.

I haven't yet found a schematic to properly wire in the Thermo Control Amp for an engine swap. I'll need to study the FSM and figure something out eventually.

Inspect your wiring to see if the Thermo Control Amp was wired in properly.
Test the Thermo Control Amp to verify it sends the proper signal when it approaches freezing temperatures.
If all else fails, you can use the 'bandaid' method and slightly overpressurize the AC Freon.

Kingtal0n · 04-07-2015, 05:21 PM

Why cant you just run the fan on higher to keep the evaporator from getting so cold?

If you are noticing that even with high fan speed it still freezes, then you have a problem getting an effective energy transfer. Either the airflow is not sufficient, or the path the air takes is no longer optimal. Is the air coming out ice cold on setting 4? I just can't believe its getting that cold in there. Here in Florida I never have this issue, so its hard for me to imagine now.

itsjustdaphne · 04-07-2015, 09:04 PM

Quote:

Originally Posted by Kingtal0n

Why cant you just run the fan on higher to keep the evaporator from getting so cold?

If you are noticing that even with high fan speed it still freezes, then you have a problem getting an effective energy transfer. Either the airflow is not sufficient, or the path the air takes is no longer optimal. Is the air coming out ice cold on setting 4? I just can't believe its getting that cold in there. Here in Florida I never have this issue, so its hard for me to imagine now.

Speed 1 or speed 4 itll freeze no matter what
and its ice cold on any speed as well, and yeah its getting really really cold in there. i did notice that when i turn the "AC" button off that doesnt turn off the compressor. Even if i put the temp on full heat mode its still cold, i dont have my heater core hooked up but still its always stuck on cold. im thinking they somehow hardwired the compressor on and it cant cycle off when needed.

04-05-2015, 06:39 AM	#1
itsjustdaphne Zilvia Addict Join Date: Sep 2011 Location: South FL Posts: 785 Trader Rating: (12) Feedback Score: 12 reviews	A/C freezes over on long drive I have an S15 SR swapped zenki with working A/C, and after a 45 minute drive or so the A/C freezes over and on speed 4 it feels like no air is coming out at all out of the dash vents. I'm certain that the drain tube is unclogged because when I park there's always water on the floor, but after driving for an hour I can pick up little icicles off of the blower unit behind the glove box. I tried keeping the A/C button off and going to full heat and it still does it (no heater lines hooked up), so the only fix is to keep the A/C off for 15 minutes and turn back it on. __________________ @ddaapphh \| @spectuned Last edited by itsjustdaphne; 04-06-2015 at 08:40 AM..

04-05-2015, 10:32 AM	#3
itsjustdaphne Zilvia Addict Join Date: Sep 2011 Location: South FL Posts: 785 Trader Rating: (12) Feedback Score: 12 reviews	I do have a FMIC, but I have flex-a-lite cooling fans on high mode when the A/C kicks on. AndIi do hear the compressor cycle on and off randomly as the A/C is turned on. __________________ @ddaapphh \| @spectuned Last edited by itsjustdaphne; 04-06-2015 at 08:41 AM..

04-07-2015, 12:42 AM	#4
itsjustdaphne Zilvia Addict Join Date: Sep 2011 Location: South FL Posts: 785 Trader Rating: (12) Feedback Score: 12 reviews	Did some more poking around at this issue after my powersteering line exploded. -_- So we hooked up some gauges to it and the numbers are awesome. Butttt it appears the compressor doesnt know how to cycle off when needed... __________________ @ddaapphh \| @spectuned

04-07-2015, 05:21 PM	#6
Kingtal0n Post Whore! Join Date: Jul 2005 Location: South Florida Age: 41 Posts: 4,829 Trader Rating: (17) Feedback Score: 17 reviews	Why cant you just run the fan on higher to keep the evaporator from getting so cold? If you are noticing that even with high fan speed it still freezes, then you have a problem getting an effective energy transfer. Either the airflow is not sufficient, or the path the air takes is no longer optimal. Is the air coming out ice cold on setting 4? I just can't believe its getting that cold in there. Here in Florida I never have this issue, so its hard for me to imagine now. Last edited by Kingtal0n; 04-07-2015 at 06:07 PM..

04-05-2015, 07:34 AM	#2
blkvrtswp Zilvia Addict Join Date: Oct 2012 Location: NY Posts: 691 Trader Rating: (9) Feedback Score: 9 reviews	AC can do this if the system has too much Freon (or whatever replacement gas is in there). Sometimes too little gas can also do the same thing. Drop into a shop that offers $30 AC check / recharge, they can quickly hook up the gauges and see what is going on with the gas pressures. Other causes would be due to airflow - is the AC condenser/radiator too blocked by FMIC, cooling fans, oil cooler perhaps? Are you using the under engine shroud? Do you have a radiator fan shroud? Also, if the compressor just runs with no cycling this can easily happen. Check to see if you can hear it click loudly on and off while running the AC. Good luck - my next year's project is getting AC to work in my swapped 'vert!

04-07-2015, 09:39 AM	#5
dbeiler Zilvia Junkie Join Date: Jun 2012 Location: Lancaster county, PA Age: 33 Posts: 465 Trader Rating: (4) Feedback Score: 4 reviews	How is your AC wired up since the engine swap? In a functional, stock setup, there are two things responsible for cycling the compressor. The first is the Triple Pressure Switch mounted on the AC drier. This switch will shut off the compressor when the pressure becomes too high or low. The second is the Thermo Control Amplifier mounted on the evaporator casing under the dash. The thermo amp monitors the evaporator temperature and will shut off the compressor when the temp approaches freezing. I've been doing some research on wiring the AC for my RB s14. I was very disappointed to discover most people will simply splice some wires at the M63 plug (passenger footwell chassis interface plug). This method effectively bypasses the Thermo Control Amp and the compressor cycles off the Triple Pressure Switch alone. With the thermo amp bypassed, the compressor will keep running and freeze up the evaporator. A few people have gotten past this by slightly overpressurizing the AC Freon. The higher pressure in the lines will activate the pressure switch earlier and more often, thus allowing longer 'break periods' for the condenser, keeping it from freezing over. I haven't yet found a schematic to properly wire in the Thermo Control Amp for an engine swap. I'll need to study the FSM and figure something out eventually. Inspect your wiring to see if the Thermo Control Amp was wired in properly. Test the Thermo Control Amp to verify it sends the proper signal when it approaches freezing temperatures. If all else fails, you can use the 'bandaid' method and slightly overpressurize the AC Freon.