View Full Version : A/C blows cold then hot when on the gas


LT1559
07-14-2012, 08:58 PM
So when I bought my car last year the ac was working when i recharged it with the diy home recharge kit and it worked fine for a week. then it went out so i took it to a shop and they said the stems were leaking so we switched those out, a week later the ac wasn't working again. I had so much going on I just left it alone and ignored it for a whole year. well a few days ago i decided to get it fixed and I took it to another shop, they tested it for pressure and leak(dye) and found nothing wrong with the ac system. It's been working fine for the past few days but today for the first time it blew hot, but after a minute it went cold again. I noticed that this would happen when the peg on the temp gauge is at the middle point. Also, when I'm under half throttle acceleration through the gears i notice that the air would stop blowing through all vents and the second i let off the accelerator it would blow through the vents again. I've never experienced this before, could a vacuum line do this? Any input would be greatly appreciated. Thanks.

wssix99
07-15-2012, 09:16 AM
Does it really blow hot or does it stop blowing at all? If the latter, then I'd say it could be a vacuum thing.

If its really blowing hot air, the issue must be with the A/C compressor. Maybe a bad clutch?

2001AntiVenom
07-16-2012, 04:50 AM
It could be under charged. Make sure the system is full of freon.

DisasterFormula
07-16-2012, 10:08 AM
SOunds more like overcharged than undercharged.

2001AntiVenom
07-18-2012, 12:37 AM
^^^ yea that's true

IceHammer
07-19-2012, 09:36 AM
Does it really blow hot or does it stop blowing at all? If the latter, then I'd say it could be a vacuum thing.

If its really blowing hot air, the issue must be with the A/C compressor. Maybe a bad clutch?

The baffles that control the cabin airflow passages are vacuum operated. More throttle = less vacuum = baffles move. You have any symptoms of a vacuum leak?

wssix99
07-20-2012, 07:04 PM
The baffles that control the cabin airflow passages are vacuum operated. More throttle = less vacuum = baffles move. You have any symptoms of a vacuum leak?

Yea, but a vacuum problem wouldn't explain hot air coming out of the vents. The vents are controlled by vacuum but the temperature is a mechanical cable and baffle.

If the air is going from cold to hot, then the A/C coil must be getting warm.

FOSTER21
07-21-2012, 07:33 AM
The compressor kicks out at certian RPM to keep you from spinning the living shit out of it.

runtwrestlin
07-21-2012, 08:25 PM
The compressor kicks out at certian RPM to keep you from spinning the living shit out of it.

Good point. Over 4000rpm it will cut off. How much "on the gas" are you talking about? Because if it only does it over that rpm, then it's supposed to be like that.

vatechguy3
07-23-2012, 09:45 AM
Mine has always done this. At WOT and above 4k rpm or so. Sometimes no air sometimes warm from bottom vents. Once i get off the gas the a/c starts working again.

Tony

LT1559
03-21-2013, 04:48 PM
Wow, sorry to leave this thread with no response I forgot all about this. Well time to bring this back from the dead lol, I can see what you guys are saying about it kickin out at around 4000 rpm but it still happens under normal driving around 2000 rpm shifts. The free-on will only last about 2 weeks before being completely drained. Took it to 2 shops and they still can't find any leaks. Is there a possibiliity the leak can be somewhere behind the dash?

wssix99
03-21-2013, 07:25 PM
The free-on will only last about 2 weeks before being completely drained. Took it to 2 shops and they still can't find any leaks.

Do you know if they did a leak check with the engine cold and hot? The expansion and contraction of materials could cause an opening to leak and then seal up the next. I once had a screw puncturing a line (a present from the factory) which leaked only when the engine was hot.

LT1559
03-22-2013, 02:25 PM
Do you know if they did a leak check with the engine cold and hot? The expansion and contraction of materials could cause an opening to leak and then seal up the next. I once had a screw puncturing a line (a present from the factory) which leaked only when the engine was hot.

Engine was hot both times cause I didn't shut off the car when i arrived

wssix99
03-22-2013, 03:30 PM
Maybe its worth leaving it with a shop so they can do a leak test with the system cold? (Even though it would be a PITA.)

LT1559
04-25-2013, 06:49 PM
I will definetely leave it at a shop I really don't want to dive into the A/C system. Another thing that I want to mention was that I still have that problem with hot air coming out of the vents for the floorboard. My HVAC controls are off and I'll be driving and once i'm on the accelerator i can feel hot air blowing on my feet/floorboards but once I let off it goes away. Could this be a vacuum problem? and Could this also relate to my air conditioning problem?

ggino85
04-30-2013, 12:01 AM
subscribed.........mine does the floor board thing. i can feel hot air coming into the car/heating up the cabin. im not sure if it is under acceleration only but i know for sure its when the car is moving, say 30mph+

LT1559
04-30-2013, 02:15 AM
Yeah mine's under acceleration, once I let off I can feel less of the air being blown.

chino_man279
05-01-2013, 01:00 PM
Have you checked the check valve for the hvac system? It should be sitting right by the passenger side hood strut - where it mounts by the pcm. Also if I'm not mistaken there is a vacuum canister down by the passenger side fog light. Check the lines with a mityvac or similar to verify everything holds vacuum.

There could be more than one issue going on here...I just had to replace the check valve on my 98 V6 last month.

LT1559
05-10-2013, 07:56 PM
Yeah I think it was the check valve, replaced it and it doesn't seem to be blowing hot air anymore.

LT1559
05-10-2013, 07:57 PM
As for the air conditioning I think it's coming from the connection to the firewall, when I shut the car off with the a/c running it hisses for a few seconds

Mike96z
08-13-2013, 07:37 PM
Mine does this at high rpm but doesn't turn back on. Blows hot after. I unplugged the pressure sensor amd worked again until I hit high rpm. Bad sensor?