Auto Repair Manuals

Most of the posts on this blog are generic in nature and are intended as a guide to repair procedures. In order to to get all the information about a particular vehicle you would need an auto repair manual specifically for the make, model and year of the car being serviced.
Auto Repair Manuals offer detailed information about the particular car they are written for. A repair manual can provide the user with locations and application of various components impossible to list in a generic description. Even thought the components discussed in this blog may be applicable to your particular car there is no way I can cover every component on every vehicle in these posts.
I do hope that you have found my posts helpful and that they have provided you with a basis for maintenance and repairs on your own vehicle.
If you intend to do the maintenance, service and/or repairs on your car I highly recommend that you purchase an auto repair manual specifically written for the particular car that you are working on.

Auto A/C Repair|R-134 Pressure Ranges

I think today we'll talk about the high and low pressure ranges on the auto a/c system using R-134 refrigerant.
First you must understand that a lot of different factors can change the pressure of the freon considerably so I'll give you ranges that the pressure should by in on certain temperature days.
On a 70 F degree day the low side should be between 25 and 45 psi and the high side should be in the 175 to 225 range.
On a 100 Degree day the low side could go as high as 60 and the high side as high as 275.
Again these are typical ranges and other factors could change them.
I don't usually get too concerned as long as the high side stays under 300 psi.
Okay now what if the pressures aren't within range?

What to look for:

• High side pressure too high

1. Condenser fan not running. If this is an electric fan make sure its on any time the a/c is on
2. Condenser coil dirty or air flow across coil blocked. Clean coil and check for air flow
3. Non condense able gases in system. Air or moisture has gotten into the system at some point. Sometimes the system can be purged on the high side to help this problem. In most cases the system should be pulled down and vacuumed. The dryer should be changed as well.
4. Blockage in the freon flow. Dryer clogged, expansion valve bad or out of adjustment.
5. System overcharged. Too much freon in the system allows no room for expansion. Pull some of the freon back out and recheck pressures.

• Low side pressure too low.

1. Low in freon. High pressure side will be reading low as well. Find the leak and recharge the system
   
2. Evaporator clogged and freezing up.
   
3. Evaporator fan not running
4. Duct controls not functioning properly
5. Freon flow restricted. Clogged dryer or expansion valve bad or out of adjustment. High side pressure should be reading higher than normal.

• High pressure side too low and low pressure side to high.
  

1. A/C compressor not running. Make sure clutch is engaged.
2. A/C compressor weak.
   

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Automotive Air Conditioning Repair|Leak Detection

Automotive A/C differs from most household units in that the components are spread out across the vehicle and connected together with various hoses and lines, whereas household a/c units have all the components contained in a small package with everything fairly easy to get to.
As I stated in a previous post the number one problem is the a/c is low or out of freon. I also said that the a/c unit does not use up freon, if it is low, there is a leak.
Freon leaks on an automotive a/c system can be very difficult to locate. Some of the most common areas that tend to leak is the front seal on the compressor, the high or low pressure safety switches and fittings where lines go together.

If the a/c system is completely out of freon you can put pressure on the system with nitrogen and check all the fittings, lines and switches with soapy water. The front seal on the A/C compressor is another matter. If you're going to be doing a lot of A/C work, a good investment is an electronic leak detector. This device has an opening in the end of a wand that allows air to pass across a sensor. It goes from a slow beep to a steady beep when freon is picked up, much like a metal detector. If the system is using R-12 refrigerant, a much cheaper device can be used to detect leaks. This is a halide torch. Propane is used for a flame that is burned under a copper element, air is drawn over the element through a tube, the color of the flame will change to bright blue if the air contains halogenated refrigerant. There is no chlorine in R-134 so the torch won't detect it. The system will have to be at least partially charged with a freon containing chlorine to use the halide torch.
One other way to find a leak is pressure testing. This can be especially useful for determining a leak in an evaporator. The evaporator is almost impossible to get to for leak checking without disassembling the dash, so it's good to know the leak is there before you start taking things apart. I usually separate the evaporator from the system, block off the lines and pressurize it with nitrogen. Do not over pressurize it, 100 to 150 psi is good. Let it sit and see if the pressure leaks down. It's not a good idea to use compressed air to pressurize an a/c system or even to blow out the lines. Compressed air contains moisture and can ruin an a/c system. Freon is not good for pressure checking because the pressure can change considerably with temperature changes. Nitrogen is the best choice for pressure testing an a/c system.
Once the leak has been located and repaired we can finish up the job. Pull a vacuum on the system. If it's been open for any length of time, out of freon completely, or air was used to blow the system let the vacuum run for several hours. Overnight won't hurt anything, we have to make sure all the moisture is out of the system. the vacuum pump should pull the system down to 29 hg and hold it there. If not, you either still have a leak , the vacuum pump is weak or there is a lot of moisture still in the system. Do not recharge the system until you can get the vacuum down to this and hold it.
Charging the a/c system by wieght is the only sure way to know it has the exact amount of freon it should have.
After I have pulled a vacuum on the system I connect my freon to the gauges , bleed any air from the line and charge the system from the high side with liquid until the proper amount of freon is in the system, or until the system balances with the freon tank and won't take any more. If the proper amount of freon is reached before the tank and system balance, do not put more in it. Do not ever charge the system on the high side with the engine or compressor running. Do not attempt to add freon to the high pressure side after the compressor has been started up as the pressure could still be high enough to burst the freon can. Only use this method for recharging when the system is under a vacuum and not running. Alternately you can charge the system on the low side with gas freon. Don't put liquid in on the low pressure side as this can cause the oil to migrate from the compressor and can cause compressor damage on startup. After the gauges have been turned off and no more freon can go in, start the car, turn on the A/C. If the proper amount of freon was not put in the system previously it can be added to the suction side as vapor at this point.

Next post retro-fitting an R-12 a/c system with R-134

Auto A/C Repair 101|A/C Troubleshooting

In previous posts I have covered the basics of how a/c works and different components found on auto a/c units.
Now we can discuss things that go wrong with a/c and how to locate the problems.
By far, most common problem found on the automotive air conditioner is either low in freon or out of freon. Contrary to popular belief freon is not used up by running the a/c. It doesn't wear out or go bad. If your car a/c is out of freon or low in freon ,there is a leak somewhere. If the freon is contaminated, it either came from an outside source or some component has failed.
First off it is almost impossible to properly diagnose an a/c problem without a set of gauges.
Connecting a set of gauges to the system will not tell you if the system is slightly low it will only let you know if there is enough freon in the system to operate. A system that is only slightly low may function fine on a warm day but not satisfactory on a hot day. The gauges will also allow you to see if the compressor is pumping properly or if there may be a blockage in the a/c system, ie clogged dryer or bad expansion valve.
Use care when connecting the gauges to the a/c system, liquid freon can cause frostbite and liquid freon in the eyes can cause blindness.With all this in mind let's do a quick check

• Start the car and turn on the A/C.

• Is the compressor running? If you can see the front of the compressor, the clutch should be engaged and the extreme forward part of the compressor should be turning. Not just the pulley portion, the actual front part is the clutch plate that drives the compressor.
• If the compressor is turning feel the lines at the back of the compressor. The small line is the high pressure side it should feel warm or hot to the touch. The larger line is the suction side and it should be cool to moderately cold to the touch. Also check the lines at the evaporator, the same applies.
• If the compressor is cycling off and on this is a good indication that the freon is probably low.
• If the compressor isn't running at all , check the a/c fuse first.
  

• If the compressor is running and there is no temperature difference or only a slight difference either the freon is low or there is a circulation problem. note: on most newer vehicles if the freon is low the compressor will not run. the low pressure safety switch will keep the compressor turned off.

• With this quick check, if the a/c seems to be cooling but the air inside is not cool, several things come to mind

1. The heat valve may not be turning the water off to the heater core.
2. The dampers in the ventilation ducts may not be operating properly.
3. The evaporator could be clogged not allowing sufficient air flow over the coils.

• If the initial check provided you with the information to conclude that the a/c was not cooling gauges should be connected for further testing.
• Don't just cram more freon in to see if this fixes the problem, remember what I said ,, your a/c does not use up freon, if it is low, there is a leak. Also if something else is wrong, overcharging can cause damage to other components.

Alright , I've got some work to do now. I'll continue our Auto A/C Repair later. If there are any questions anyone has, just ask in the comments and I'll try to help.

Auto A/C Repair/Component Basics

From a previous post I described the basic components of the air conditioner system and how a/c works. We'll go over these and cover a few more components that are related specifically to auto air conditioning.
The Compressor will be mounted somewhere on the front of the car engine and is belt driven. This is the pump that circulates the freon through the a/c system. On the front of the a/c compressor is an electro-mechanical clutch. When power is supplied to it by turning the a/c on, the clutch is energized and the compressor is turned by the engine.
The Condenser is the part of the a/c system that removes the heat from the freon and it is located in the front of the car usually right in front of the engine radiator. It looks like a small radiator or oil cooler.
The Evaporator may be located inside the car usually under the dash. It is contained inside the ventilation box along with the heater core and typically very hard to get to. This component is used to remove the heat from inside the car by recirculating the air over the evaporator coils by way of the blower fan. It looks like a small radiator or heater core. Some vehicles have the evaporator mounted in a ventilation box on the passengers side firewall under the hood. Most General Motors products use this arrangement. Some vans and SUV s actually have 2 evaporators. They have a separate unit for cooling the rear of the vehicle.
One of 3 devices is used to control the flow of freon to the evaporator on most auto a/c units;

1. expansion valve
2. expansion block
3. orifice tube

The expansion valve, if equipped is usually located in the box with the evaporator. It will have a tube with a remote bulb on the end connected to the outlet side of the evaporator.
the bulb senses the temperature of the freon leaving the evaporator coil and the expansion valve regulates the freon flow accordingly.

The expansion block is usually located under the hood , near the firewall where the inlet and outlet lines from the evaporator emerge.It is connceted to both , the inlet and outlet line of the evaporator.

the orifice tube will be inside the inlet line of the evaporator at the firewall where the lines attach to the evaporator.

A high pressure safety switch is generally located somewhere on the compressor. If there is a wire attached to the compressor, ( not to the compressor clutch) this is a hps switch.This switch stops the a/c if the high pressure side exceeds its limits.

A low pressure safety switch is generally located somewhere close to the evaporator.
It will be in the suction side line leaving the evaporator ( the larger line). May also be located on the dryer/accumalator. This switch stops the a/c if freon gets low or the low pressure side falls below its limits.

The dryer/accumalator is usually located close the the evaporator usually on the left side fender close to the firewall. This is used to remove moisture and contaminants from the freon and serves as a storage container for the freon in the system.
note:
Some cars have the dryer by the condensor in front of the radiator. You may also find the hps switch there on some cars.

Most vehicles use either R-12 freon or R-134 freon. R-134 is used to replace R-12 in older cars as it is more environmentally friendly than R-12. If your car is older and still has R-12 in it , It will need to be retro-fitted to use R-134.

I think we've covered the majority of a/c components on most autos of today so we'll move on to A/C Troubleshooting in the next post.