Easy way to check the A/C?
Thread Starter
On The Tree
Joined: Apr 2007
Posts: 145
Likes: 0
From: Boise, ID
Easy way to check the A/C? It finally got hot enough out here today for me to run the AC. I THINK I ran it earlier this year and it was ok... I seem to remember it not seeming as cold as normal, but I kind of blew it off (or maybe I'm imagining things because I'm thinking too hard about it 
).
Anyway, I turn the A/C on and it just blows hot. The engine is suppose to rev up a little when you turn the A/C on, but it doesn't happen. I check the fuse (good) and the relay (good). I also used my DVM to check the line that the PCM draws to ground when you turn the A/C on... it's not going to ground, so the PCM is not sending the A/C request. According to the manuals, this could be a number of things, but I'm thinking the most obvious is low R-134 (if you're low pressure, it won't even try to engage the compressor clutch).
So my question: Is there an easy way to check the pressure? I think I know where the PCM gets the pressure from, so I could read that with a DVM, but I don't know what the reading SHOULD be... Should I just take it into a shop?
I had my engine replaced last August and I'm guessing that they just didn't put the A/C back together quite as well as it was originally so now I'm leaking.
).Anyway, I turn the A/C on and it just blows hot. The engine is suppose to rev up a little when you turn the A/C on, but it doesn't happen. I check the fuse (good) and the relay (good). I also used my DVM to check the line that the PCM draws to ground when you turn the A/C on... it's not going to ground, so the PCM is not sending the A/C request. According to the manuals, this could be a number of things, but I'm thinking the most obvious is low R-134 (if you're low pressure, it won't even try to engage the compressor clutch).
So my question: Is there an easy way to check the pressure? I think I know where the PCM gets the pressure from, so I could read that with a DVM, but I don't know what the reading SHOULD be... Should I just take it into a shop?
I had my engine replaced last August and I'm guessing that they just didn't put the A/C back together quite as well as it was originally so now I'm leaking.
A set of manifold gauges can be used to check the pressure (at the service ports). Ours should have an electric clutch on the compressor which would engage/disengage it, nothing to do with the pressure (compressor changes the low pressure vapor into high pressure vapor).
Now if you have a low charge and have air/moisture in the system or an air leak your cutout switch or cycling switch (which is what we should have since we have an accumulator) may not be allowing to clutch to engage (either too much pressure at the cutout or too little at the cycling).
Now if you have a low charge and have air/moisture in the system or an air leak your cutout switch or cycling switch (which is what we should have since we have an accumulator) may not be allowing to clutch to engage (either too much pressure at the cutout or too little at the cycling).
mine is the same sort of i never use the ac because its not as cold to me as the MAX position.i also remember from a old shop teacher saying to run the heater on a warm day every so often for a few mins to let everything just circulate.
TECH Senior Member
Joined: Dec 2001
Posts: 5,399
Likes: 3
From: Jacksonville, FL
Check the static pressure with gauges, key off, car in the shade. If the ambient temperature is above 75* the PSI should be at least 70/above 90* should be 100 psi. If it's nil or low try adding a can of referigerant that has dye in it - it's leaking somewhere.
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Don't take that advice and add a can or two... that's incorrect.
If they had your engine out, I'm willing to bet they did not replace the reciever/dryer when it was put back together. These have a bag of dessicant located inside. Once you've cracked the system, they can only be left open for ideally 5-10 minutes. After that the bag of dessicant inside the reciever/dryer absorbs too much moisture and is junk.
So, IMO it's best to take the car to a reputable shop. Have them do a reclaim on the system and get out whatevers in there if anything. Have them replace the reciever/dryer and throw a vacuum hold at the system. They will charge it with the CORRECT amount of refrigerant afterwords and you will be good to go.
Part of the service should also include them adding dye to the system, and also checking for any leaks with a UV light after they have run/ tested the car.
I'd be willing to bet you are correct on your diagnosis...
If they had your engine out, I'm willing to bet they did not replace the reciever/dryer when it was put back together. These have a bag of dessicant located inside. Once you've cracked the system, they can only be left open for ideally 5-10 minutes. After that the bag of dessicant inside the reciever/dryer absorbs too much moisture and is junk.
So, IMO it's best to take the car to a reputable shop. Have them do a reclaim on the system and get out whatevers in there if anything. Have them replace the reciever/dryer and throw a vacuum hold at the system. They will charge it with the CORRECT amount of refrigerant afterwords and you will be good to go.
Part of the service should also include them adding dye to the system, and also checking for any leaks with a UV light after they have run/ tested the car.
I'd be willing to bet you are correct on your diagnosis...
The fastest way to check is to look in the sight glass. It will either be on top of the dryer or inline on one of the hoses. It should be completely clear. Bubbles indicate a low charge. Clear indicates either a full charge or a completely empty system.
You can also check to see if the clutch is locking. If it is not, either the system is empty or there is an electrical problem.
But if they opened the system, you have to go through the steps outlined by BA TA. You'll be glad you did.
Also, as mentioned previously, the system needs to be run periodically to lube the seals and keep them from drying out. Such is life.
You can also check to see if the clutch is locking. If it is not, either the system is empty or there is an electrical problem.
But if they opened the system, you have to go through the steps outlined by BA TA. You'll be glad you did.
Also, as mentioned previously, the system needs to be run periodically to lube the seals and keep them from drying out. Such is life.
TECH Enthusiast
Joined: Mar 2002
Posts: 554
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From: NY
Originally Posted by 408Maro
i also remember from a old shop teacher saying to run the heater on a warm day every so often for a few mins to let everything just circulate.
there's always engine coolant running through the heater core everytime it's running regardless of the a/c on or not. 