[pjm]

When I try to use my a/c for the first time this year it only blows out hot air. Even if I turn the a/c off and just turn the knob to cold setting it still blows hot. The temp gauge looks ok so I don't think it's overheating. Any ideas what might be the problem? It's scheduled for service on wednesday so I'd like to know what kind of bill I might be looking at.

Thanks in advance.

 

[brokenknee]

It may just be low on refrigerant; is the compressor kicking in? If the refrigerant is to low the compressor will not kick in.

If it is low, that means there is a leak and it should be repaired.

 

[pjm]

I'm not sure if it's kicking on, but why would it still blow warm air even with the a/c off and the temp control to cold? That shouldn't have anything to do with the compressor would it?


I'll see if it kicks on tonight.

 

[47_47]

Without the AC on, the coldest that the air can be is temperature at the air inlet. Agree with brokenknee, you probably are low on freon and have a leak.

 

[Clutchcargo]

I'm not sure if it's kicking on, but why would it still blow warm air even with the a/c off and the temp control to cold? That shouldn't have anything to do with the compressor would it?


I'll see if it kicks on tonight.

It could be that the mix door is stuck open. I believe it's vacuum operated.

 

[Hobb3s]

hmm so how much would he be expecting to get charged?

I went through this with my Acura... same thing.. no cold air, compressor kicked in and all. Replaced some of the lines that run the refrigerant. $500, the recharge on the freon stuff is expensive. 2 months later same problem, replaced another line (another $400), worked for the rest of the summer, next summer the problem returned, but I'm done paying for it.
Thus my advice is, if you have the cash to spend make sure they find the leak and replace all the parts you can afford if you really want the air to work again, cause recharging the freon is expensive. Try not to turn it on while it's low on freon though, that could kill your compressor, the compressor is lubricated by the freon.. could end up costing you more to replace that as well.

 

[brokenknee]

The compressor should not kick in if low on refrigerant. It is protected by a low pressure switch, it is possible for the switch to go bad and thus ruin the compressor. The compressor is not lubricated by the refrigerant, it is lubricated by PAG or ester oil; in older R12 systems it is mineral oil. While most oil stays in the compressor some oil is carried by the refrigerant through the system, when there is a refrigerant leak you loose a small amount of oil with the refrigerant. If you loose enough refrigerant and do not add any oil back into the system you will eventually burn up the compressor.

If you have had the vehicle since new and know there hasn't been any leaks before you can safely add refrigerant to it without worry. It is were you have had to add refrigerant on a regular basis is when you should add some oil. How much is pretty much a guess, usually just an oz or two at the most. Be careful not to add to much oil as it is a non condensable and will effect the cooling capabilities of the system.

When adding refrigerant a general rule of thumb for the high side pressure is 2 1/4 to 2 1/2 times the ambient temp. So if the ambient temp is 80* the high side pressure should be 180 psi to 200 psi. I want to make this clear this is a general rule of thumb and different systems could be higher or lower than this. The low side should be between 30 and 40 psi. Again a general rule of thumb. Overcharging the sytem will also effect the cooling capacity of the system.

Another way to charge the system is by vent temps, put a thermometer in the center vent and monitor the temp as you add refrigerant. Add only an oz or so at a time. Let the system run a couple of minutes until the system stabilizes, measure the temp. Once the temp no longer drops stop adding refrigerant.

You can also measure the inlet and out temp on the evaporator. There should be a 10 to 15 degree difference between the inlet and outlet.

Yes air conditioning work is expensive, make sure you go to a reputable shop. There are a lot of shops that have a guy with a set of gauges and claim to experts.

Remember if you have to add refrigerant you have a leak, find the leak and get it repaired. There are dyes that you can add to the refrigerant that will show up under a black light. There may also be an "oily spot" were the leak is, but may not always be the case if the leak is small.

 

[Clutchcargo]

I went through this with my Acura... same thing.. no cold air, compressor kicked in and all. Replaced some of the lines that run the refrigerant. $500, the recharge on the freon stuff is expensive. 2 months later same problem, replaced another line (another $400), worked for the rest of the summer, next summer the problem returned, but I'm done paying for it.
Thus my advice is, if you have the cash to spend make sure they find the leak and replace all the parts you can afford if you really want the air to work again, cause recharging the freon is expensive. Try not to turn it on while it's low on freon though, that could kill your compressor, the compressor is lubricated by the freon.. could end up costing you more to replace that as well.

That's been my experience as well. Once the AC goes, it's a $3-400/yr charge to keep it running.

 

[Hobb3s]

Brokenknee: Sorry about my misinformation. I was just reciting what I was told by my mechanic about the compressor. You mention that you can add refrigerant to it to the system. I think it depends where you live, because the environmental laws here (ontario) prohibit unlicensed persons from handling the refrigerant you have to get an ODP card and training.

Also just to note why it is so expensive, at least what they told me is that every time they work on it, it have to drain all the refridgerant and replace it. So you pay for the full fill up of the stuff each time they make a minor fix to the system.

 

[MikieMike]

auto AC

Thankx for the info. I thought when a mech repaired a AC unit the freon was recovered and replaced after the repair? True or False ?
MikieMike

 

[brokenknee]

Refrigerant has to be recovered when working on any system, you are not allowed to vent it into the air. The only exception for this is a minimum amount you may lose when connecting your fittings.

By law you are allowed to reuse that refrigerant in the system you took it out of only. You are not allowed to use it in another system.

Since R134a is still relatively cheap (about $4 # last years price, I haven't priced it lately) and most modern car systems take less than 2#s it is not a huge cost for the shop. They also know they have good clean refrigerant in the system. Contaminated refrigerant may have been the problem the system was not cooling properly to begin with.

A shop needs to evacuate the system in order to make the repair; by law any system that leaks a certain amount per year (sorry don't know the amount) must be repaired. Once the repair is made they need to pull a vacuum to pull out the non condensibles and verify there is no leaks. They should use a micron gauge to do this. Vacuum gauges are just not accurate enough to verify there is not a small leak.

As far as the cost to have a system repaired. It can be very time consuming to find and repair the leak.

Here in the States you are still allowed to purchase R134a to "top off" your system without a refrigerant card; I am sure that will change over time.

 

[47_47]

As far as the cost to have a system repaired. It can be very time consuming to find and repair the leak.

How true. On a very low system, you will have to add R134a to locate the leak, test system operation and recover.

Think of the AC system as a water hose. Remove the nozzle and turn on the water. It follows the path of least resistance and flows out the open end (major leak). Put the nozzle and water back on and find the pinholes (minor leaks). Your car is not stationary and the AC lines and connections must have flex. Flex your hose and you get another source of leaks. Restoring and operating a system back to proper pressures will eventually leak at the next weakest link.

 

[pjm]

Well my wife took it to the dealer and the first step to trouble shooting it is to refill it with freon and a dye that will show where the leak is...... hopefully. The air is cold once again with the recharge and I will be taking it back to the shop on Friday to see if they can find the leak. It cost me $125 for the recharge and if they find the leak I get 1/2 off the labor charge because I already gave them 125. I hope they find the leak because if they don't I will be having the same problem again when it leaks out.

Thanks for the replies hopefully this thread will help out another user when they run into a similar problem.