A/C sometimes blows hot air & sometimes cold..don't think its the compressor...

[LolaAnnGram]

2006 Saturn Vue 6 cyl - What causes AC to OCCASIONALLY BLOW hot air? The other day when it happened, I shut AC off then turned on = pushed the AC button on and off & it actually worked. This has been happening for awhile and seems to produce a burning smell.

After trying to find answers before taking it to mechanic, it seems it could be the relay switch or compressor. The compressor was replaced 2 years ago so I can't imagine that's the issue...

At one point, I was reading up on a possible bigger problem and that this could be just a symptom....I can't find that article now...everything the author described is everything I was having happen?? Any ideas.

Also, FYI I just had no compression engine torn apart & replaced with all OEM (??) parts & the car runs like its never ran! This AC problem happened before the engine fail (which was caused from pothole - see other thread if interested in that) & continues to be problematic....

I'm a clueless 56 year old ditzy blonde

[fdryer]

* Can you identify the burning smell? This may help since no one here is standing next to your Vue to smell any fragrances emanating from an odiforous vehicle.( lavender, Chanel #5, pine scented air freshener excluded)

* Intermittent ac operation can be a result of any number of issues that may be beyond your ability to troubleshoot. Other than a fuse check or swapping fuses, advanced troubleshooting of ac problems requires knowledge of ac systems, using refrigeration gauges, and more. Perhaps asking your mechanic if he's able to diagnose and troubleshoot this ac problem or can refer you to someone better experienced may be a better way to go than attempting to use any suggestions given here. Personally, I think anyone attempting ac repairs becomes the ac repair person whether trained or not as refrigeration is as complicated as electronic fuel injection, turbo/super charging, electricity, electronics and computers (vehicle or general computer systems). Store ac refill cans with simple instructions does not make anyone knowledgeable about ac repairs with most throwing away money on refill cans on unsuccessful against actual repair success.

You don't have to accept my opinion on this as you're free to search any forum here regardless of model to read about ac diagnosing, troubleshooting and repairs made by diyers. Vehicle ac systems are mostly the same insofar as overall operation once the compressor runs. The control systems vary from model to model like automated climate control where a driver simply dials in the desired temperatureand selects either auto/manual fan speed or manually moving a temperature lever and selecting fan speed.

[Bruce Rock]

Since at times it blows cool air, I would agree it's most likely not the compressor. My first guesses would be the scroll valve (about $50 for the part) or low Freon. If you could be more specific of the conditions under which you have cooling and when you don't, we might be able to narrow it down

[LolaAnnGram]

TY - Yesterday I got in and turned on AC and all fine. Keep in mind Im in south florida so it runs and runs and runs due to never ending heat/humidity. Wondering now if it has something to do with days that are really high humidity now that you asked about that....the first time it happened was when i had an "in town" 60 mile round trip-stop go stop go errand run....went on interstate and stuck at traffic lights several times. On interstate it was perfectly fine...when I let it idle while running into an office I came out and hot air. Next day it was cold air....2 weeks cold then back to hot...

[Bruce Rock]

Originally Posted by LolaAnnGram

TY -.the first time it happened was when i had an "in town" 60 mile round trip-stop go stop go errand run....went on interstate and stuck at traffic lights several times. On interstate it was perfectly fine...when I let it idle while running into an office I came out and hot air. Next day it was cold air....2 weeks cold then back to hot...

From this description it's hard for me to determine WHEN you had cooling and WHEN you didn't.

But taking the last portion, "On the interstate it was perfectly fine...when I let it idle while running into an office I came out and hot air."

That fits the problems a bad scroll valve displays.

[fdryer]

I re-read the post and agree this may be another scroll control valve issue. If highway driving or above a certain speed results in cold ac but low speed stop and go results in warm air then the scv may be faulty.

To understand scv issues, troubleshooting, symptoms and repairs, this link may help; http://www.saturnfans.com/forums/sho...+control+valve

[LolaAnnGram]

TY - No Chanel #5 here! I tried the whole AC canister BS on an old van - will NEVER waste money again on that....I am going to take it to mechanic but since I am an old lady, I want to understand as much as possible cuz automatically it seems to always be the most expensive path that some mechanics take...I trust this guy but its so frustrating to have them explain in what to me is Chinese. No clue! TYTYTY

[fdryer]

"The most expensive path some mechanics take.." is a polite way for unscrupulous people to profit from many car/truck/suv owners unfamiliar with ac repairs. Replacing the compressor is the most expensive part (plus markup) along with a canister combining a dryer and filter mounted next to the condenser coil. Add hourly labor rates and expensive refrigerant (also marked up) are reasons ac repairs are expensive. This supports unethical repair people capable of making more money than honest repair shops. Compressors rarely fail with the exception of Fords and Vues using the same compressor. There are three types of compressors; piston, vane and scroll compressors. Piston and vane compressors are reliable. Scroll compressors used in Fords and Vues seem to have a recurring fault with its scroll control valve, a $35 part on the compressor. This failure doesn't seem to fit your descriptions of your cold/hot running ac system but the following failure mode may help to confuse, illuminate, confirm the problem is elsewhere in the ac system or your descriptions do match a faulty scroll control valve issue.

When a scroll control valve becomes faulty, the typical symptoms are low cooling at stops and local traffic but excellent cooling at speed like highways. The scv fails to regulate refrigerant inside the compressor to provide cooling whether idling or at highway speed. With this problem recurring, I don't know if Ford or GM put out a service bulletin to have dealers replace the scv and not the compressor. Members here discovered this fault, passed it on for others capable of performing diy repairs at home using all the equipment repair shops use. Refrigerant must be removed into reclamation canisters either for reuse or disposed of according to epa regulations. This adds to a repair bill. Even without epa regulations, refrigerant must be removed before opening a system for repairs. Removing and replacing the scv is straight forward then ensuring everything is sealed correctly before a repaired system is evacuated of air and moisture before refilling with refrigerant. This explanation is about refrigeration if anyone is interested in becoming a repair tech. Labor rates reflects repair shops overhead costs and profits to support a business. Small repair shops performing the same repairs may do less costly honest repairs while keeping labor rates lower for customer bills, saving them money. The difficulty is finding honest, reputable repair shops with word of mouth possibly the only way to know. Advertisements costs money compared to word of mouth.

Honest ac mechanics can tell the difference between a faulty scroll control valve and faulty compressor. Dishonest and/or clueless mechanics won't care to know the difference as there's money to be made on big ticket parts compared to replacing a small part. In the end, both repairs can be compared in overall total costs with the scv replacement the lower of the two bills. How much depends on the breakdown of costs. There may be up to a few hundred dollars difference. An expert with experience and knowledge separates themselves from dishonest costly repairs.