notn41

My A/C fan always works. But randomly it will stop blowing cold air and only blow hot air. I have intake/long tubes/mild-large cam and tune.

What could be the cause of this?

It's summer in las Vegas and not having A/C is killing me.

tim414

Sounds like the head unit may have something going on. Every once in a while my Yukon will blow hot air when the thermostat is set to cool temp. When I stop it and turn it off for a min or so and crank it, then it back to norm. Almost like the system reverses and blows heat when cool is needed. I say every once in a while, it's happened three times in doubled number years

whatcop?

What are your coolant temps? If they get too high the ac compressor will be disabled to allow the cars temps to come back down.

tjwong

Your refrigerant charge maybe to high. Have it discharged and recharged. The system capacity is 1.1 lbs, anymore than that in your climate and you will have problems. There was a TSB addressing this issue some time ago. An excessive charge amount causes excessive high pressure in the system which results in intermittent operation especially in hot ambient temperatures.

tim414

Seems like it would have showed it face before now. I think he has a '08....so I would think it would have surfaced before now....????

Following this because I have a similar issue in my Yukon. It works fine and suddenly it will reverse and heat will kick in. I read the issue is found in either the head unit that controls the thingy under the dash or that thing under the dash. This is how it acts as it begins to fail. Read this on the Taho/Yukon forum.

VetteVinnie

This is exactly what mine was doing after heads/cam/headers in the extreme Houston summer heat/humidity. I've tried various things to eliminate the problem. Dealer at one point replaced the expansion valve, but that didn't seem to fix it. And it was that same year that I ended up melting the fan plug and almost overheating the engine. I saw the temps jump way up, but I shut down the car before any damage occurred. I wiggled the fan connection and got them working well enough to get the car home. Now I have bypassed the fan connector and directly connected the ground wire.

Last year, I was still having a few instances of this problem. So as an experiment I popped the hood when the problem was occurring and discovered that the problem did not occur with the hood open. My conclusion (until I test it this summer) was that the underhood temperatures were interacting with the A/C lines and causing excessive pressure in the system. If the pressure gets too high, the compressor shuts down. One of the lines is not too far from the extremely hot header on the passenger side.

When I had my heads redone late last year, I had the headers ceramic coated to try to cut down on the underhood temps. So far, so good, but temps haven't gotten above 90 for too long. I'll report back after running it around in 105+ this summer. If I still have the issue, next step is to try to insulate the A/C lines better to protect them from the heat. If that doesn't work, then the only thing I can think of that would correct the problem is to get a vented hood.

EDIT: Side note, overheating and excessive temps were worse with the Vararam. Now it has the Callaway Honker. That change alone significantly improved the problem, but did not completely eliminate the A/C issue. Hopefully the ceramic coating on the headers will cut the temps just enough to prevent the problem.

Carnac

This happened in my 05 coupe. I also live in Las Vegas. Hot in traffic, too much coolant charge will trigger the high pressure A/C coolant sensor and turn off the compressor (hot air follows). This happened most on 100+ days with stop and go traffic.

To get the most out of the A/C, shops/dealerships will try to add a little extra refer gerent (and this does help as long as you are moving).

I have had the same problem with my 08 Z06, but to a lesser extent. I have elected to run with the full or little over full charge to get more cooling in exchange for the occasional in traffic problem (I seldom drive it when it is super hot and traffic is going to be bad).

Jim

tim414

I know apples/oranges...what I was saying while I have not had this happen in the 'Z, very similar issue happened with my truck. There have been instances with those.

One minute it works fine (driving normally) and then it changes from cool to hot (you can tell the system is applying heat because the temp in vent is much warmer than outside air. Almost like the outside air temp changed from 95 to 35 and the system responding accordingly by applying heat. I stopped/turned off the ignition for minute or two and then re-start the engine. It flips back blowing cold air again in 95 deg outside temps like it should. I had this happen 3 times I think. 2 of those were while driving and the other I was sitting in line at Starbucks for a iced Frapicino (sp?)....those are great by the way....

So, just trying to help out...I know it's not my Vette, but it's similar issue and I'm sure most these type parts/head units all come from same place.....I had read on the Yukon forum the issue (in those anyway) with with climate control. Good Luck.

1320IN9

Sounds like high pressure or some debris stuck in the receiver drier causing the system to shut down, if you can recover what is in the system to see if it's overcharged, if not then I would look into the drier

jedblanks

I had this problem on my nissan. It was the compressor clutch.

Does your Ac work better on cool/cloudy days?

Hotter days cause
A)higher temps under good
B) higher head pressure at the compressor

This electric clutch works by using voltage to close a small gap between the pulley and the compressor. This allows the compressor to engage/disengage while the belt continues to turn.

As the clutch wears, high head pressure can cause clutch to slip and not turn. When it stops turning, the Ac slowly gets warm. The it cools, reengages and Ac gets cool again. Sometimes revving the engine would cause it to engage.

Just a suggestion of one thing to check.

VetteVinnie

This problem happened to me on my 1999 Trans Am. It had a defective compressor from the factory. It would cut out while driving. My Vette, however, only cuts out when the car is sitting still (at a stoplight, in a parking lot). It's fine as long as the car was moving. To reproduce it at the dealer, I would start the car and hold it at a higher RPM (3-4K) to heat it up, then it would cut out. Several times the dealer couldn't reproduce it so I had to demonstrate it to them.

Again, this only started happening after the headers went on the car. My scenario is very close to what the OP describes.

There are several threads on this where we've talked about this problem before.

Here's my post when it first started happening to me:

http://forums.corvetteforum.com/c6-z...tting-out.html

And here's the follow-up where the dealer initially said that the alternator was the problem. They subsequently replaced the expansion valve:

http://forums.corvetteforum.com/c6-z...off-wierd.html

So, changing the Vararam to the Callaway and ceramic-coating the headers should hopefully fix this once and for all.

notn41

All very good info. I am a little confused as to what to do with all of the responses. Check the pressure, wrap the AC lines, coat the headers?

jedblanks

If you have access to AC gauges, check the pressures. There are charts on the web that will tell you what the pressures should be on the hi and low side based on ambient temperature.

If you can manage to run the car and the AC while viewing the compressor front, you can make sure the pulley is turning. You may have to have the car in the air to see it. Or a very good light. Watch out for moving parts. The belt turns the outside of the pulley all the time, but the center of the front of the pulley only moves when the clutch is engaged. When it gets hot, is the clutch moving?

If all that appears well, then it could be the HVAC actuators (blend doors) or something else with the control unit. Should set a code though.

notn41

Okay so this is what happens, the AC works fine when the car is cool when I first start it. But when I let it sit for 15 minutes, the air starts blowing less and less cool until it starts blowing no more cool air.

I have looked inside the engine bay but I am no AC expert so I don't even know which parts to look at or which parts are connected to the AC system.

BigMike NY

Funny, my A/C just started doing this, its blowing very warm air, even with the A/C on 60* and the cabin air circulator on. When I bought the car last year it blew ICE ICE cold air, now it is not...

Mods in my sig, does that have anything to do with it?

AzMotorhead

I hope I can answer most of all your questions.
If your AC blows cold while your moving but starts to blow warm or slowly warms up while your sitting still/idle. It's because your not getting enough air flow thru the condensor in front of the radiator. If you have a Vararam or other aftermarket air intake your air flow is being obstructed from stock configuration.
Make sure your fans are running at speed and coming on when they should. Also ensure your condensor and radiator are clean and not clogged or restricting airflow.
If your not getting the required air thru the condensor the head pressure(Hi side of AC system) will increase.Potentially causing the Hi/Lo pressure switch to open,and cut power to the compressor.Assuming comp is still engaged. If insufficient cooling air passes thru the condensor the Refrigerant cant condense from a Hi pressure gas to a hi pressure liquid. It'll stay gaseous and pass freely thru the orifice tube(expansion valve).
AC works by absorbing heat as it boils off>Changing from a hi pressure liquid to a low pressure gas<
If you change pulleys on your crankshaft you alter the speed you compressor turns affecting its output at idle.
Best thing to do is hook up a set of gauges and read the pressure both Hi and low at Idle and 15-2000 rpm.
Hi side should not be over 250psi. Low side pressure is directly related to temperature. 35psi is going to be right around 35* for R134. Ambient temps are going to play a factor in air temp out also. A properly serviced system should be able to give you a 40* drop in ambient temps. If its 105 outside and you get your system to drop in car temps to 65* it's going to feel damn chilly in the car.
Wrapping the lines from the condensor to the firewall will have little to no affect. That header isnt getting any hotter than the stock manifolds.

AzMotorhead

Big Mike in NY. sounds like you've had a loss of some refrigerant look for oil staining at the line connections and check the serving ports Schrader valves for leaking.
Dont just start adding refrigerant because overservicing will inhibit the system just as much as running it underserviced.
C5's and C6's are bottom feeders. Meaning all the cooling air for the rad and condensor are being pulled from beneath the front bumper. The condesor is going to get clogged with road grime and debris. Giving it a good wash with simple green and a strong water hose will help.
try to flow the water from the back to front thru the fins.
Also I've seen some cars where the radiator has been tilted back from factory configuration and the fans hadnt been properly positioned so airflow thru the cond and rad were diminished.

AzMotorhead

Tim the GM trucks are noted for having a control panel problem.
Thats what it sounds like on your Yuk/taho

erikszr1

azmotorhead

millerjj

I just got my car back from headers, cam and Varram cold air. My ac stops working at idle then works as soon as I get going. The A/C worked perfect before. Do you think it is the cold air doing it. I noticed it blocks alot the front of the car now