A/C troubleshooting

[krmiller07]

I know the subject of air conditioning rarely come up on here. But are there any of you out there that have any A/C trouble shooting experince? Mine was converted over to R134a due to the misleading lack of availability of R 12. Now it doesn't seem to blow as cool as it used too. I checked it with one of those over the counter recharge kits (R 134a) and the gauge on the can reads 'alert'. Is it possible to overcharge the system? I thought I read some where that over charging can actually degrade the cooling properties of the system. (May have been the FSM). With the temp around here suddenly reaching 100 + it would be nice to not have to ride in a mobile sauna on the way to work. most of the shops around here are swamped and want an arm, a leg, various othe body parts and next months pay tp look at it. My guess is they'd come back with enough 'repalcement parts' ( due to the age of the truck) to scare the hell out of me, or to completely re do (outfit) the whole truck.

 

Any suggestions or ideas before I cave in and go to a 'tech'

 

Thanks

Edited June 8, 2011 by krmiller07

[trogdor]

I took mine to a tech and it now blows super super cold it was well worth the money, It cost me $32 to have it checked and charged and a belt put on. I would think that you have a leak somewhere in your system, that is what it sounds like to me.

[nunya]

Might be worth it to get it vacuumed down and charged with the correct ammount of freion... I charged my r12 system with 134a and the only 'modification' I did was use a 134a low side fitting I keep FOR the fact I have more than 1 r12 vechile. Icy cold

[krmiller07]

Might be worth it to get it vacuumed down and charged with the correct ammount of freion... I charged my r12 system with 134a and the only 'modification' I did was use a 134a low side fitting I keep FOR the fact I have more than 1 r12 vechile. Icy cold

Nunya,

 

When you charged your system did you go coolant weight or preassure using a Hi/Lo gauge and vacum pump to evacuate the system ?

[krmiller07]

Might be worth it to get it vacuumed down and charged with the correct ammount of freion... I charged my r12 system with 134a and the only 'modification' I did was use a 134a low side fitting I keep FOR the fact I have more than 1 r12 vechile. Icy cold

Nunya,

 

When you charged your system did you go coolant weight or preassure using a Hi/Lo gauge and vacum pump to evacuate the system ?

[nunya]

i used a vacuum through a high/low gauge (only using the low side) and don't remember the amount honestly (theres an equation somewhere for the weight difference between r12 and 134a, haven't needed it in a while so I don't remember it to be honest as well) but went by the weight amount with freion charging... But I am spoiled with tool access too

[JamesRich]

connect your gauge and hold the engine at a 2000 rpm rev and see what the pressure drops to. It should be around 20 to 25 psi but not any lower. As compressors get older they don't pump as well at low rpms so I always check them at a rev. You would really need a set of gauges connected to see what the high side is doing, if the expansion valve is stuck open it will give you a high low side reading too.

Look at your sight glass on the drier right behind the grill, do you see air bubbles passing by or oil? When I converted mine I added 8 oz of the 134 compatible oil without removing and draining anything so now I have too much oil and I can see it flowing passed the sight glass. So mine cools but not like it should. If you just see air bubbles your system is low on refrigerant.

A/C system are really simple, refrigerant gets cold from being sprayed from a high pressure to a low pressure. Too much oil will interfere with the heat transfer in the evaporator but other than that if you have enough refrigerant and the expansion valve is regulating the pressure differential right it will cool. Provided your evaporator and condenser are not plugged up with stuff keeping the air from passing.

James

[Alkorahil]

I concour with JamesRich, especially about cleaning out the evaporator on these older vehicles. Just doing that can make a big difference.

[frozenrotors]

Ok, I tend to agree with James. Especially since he's a customer ! LOL. So...how does one go about cleaning out the evaporator? And more importantly...where's it located!

 

I have already taken apart the plastic box behind the glove box, but I believe thats where the heater core lives? Although I did see the expansion valve in there. I tried to clean out the leaves that I thought may have accumulated in there, but it was actually pretty clean. If this is in fact the evaporator, I'd like to know how you can clean between the cooling fins and flush or vacuum out the dust and crap that may be trapped in there after all these years. BTW_ I thought there was a post on here about removing this box completely? I could only get the front spring clips off (and the nuts and bolts), and that wouldn't allow me to completely remove the lower section.

 

Thanks

[Alkorahil]

Go to your local dealer or parts store and ask for a can of evaporator core cleaner.

 

To get to the evaporator:

remove the glvoe box

remove the black metal panle behind the glove box

you will now be looking at the AC unit. The fan is on the right, the evaporator is onthe left.

on the evaporator there will be a metal module screwed into it and facing you. (this is the blower motor resistor) It has wires coming out of it. unplug the module and unscrew it from the evaporator and remove it.

lookinside, to the left in silver is the evaporator. It looks like a small radiator.

You will also probably see leaves and crud inside of hear.

gently remove this stuff from the evaporator catch. you can use a vacuum if you like.

be careful not to touch the evaporator to be safe as it is easy to damage it.

 

 

you shouldnt only need a philips head screwdriver for this project. A flashlight would be helpful too.

[krmiller07]

Thanks guys,

 

I guess I know what I'll be doing this weekend !

[Alkorahil]

Thanks guys,

 

I guess I know what I'll be doing this weekend !

 

 

As a follow up, cleaning the leaves and junk that accumulates in the trap is something you should do at least once a year. LEaves and such can build up in there over time and cause a fire. A few people on here can give testimony.

[Desert89]

If you just converted over to R134a and it immediately was not as cold that actually makes sense, and there is probably nothing wrong with your system. R12 has a higher specific heat capacity, so in any system it will run colder with r12. Newer cars compentate for that by making the condenser (the radiator part of the A/C) much larger than the old r12 condensers to get the same amount of cooling.

[JamesRich]

If you just converted over to R134a and it immediately was not as cold that actually makes sense, and there is probably nothing wrong with your system. R12 has a higher specific heat capacity, so in any system it will run colder with r12. Newer cars compentate for that by making the condenser (the radiator part of the A/C) much larger than the old r12 condensers to get the same amount of cooling.

From my experiences that doesn't always hold true. In american vehicles with the orifice tube to regulate the flow it does because it's a set size. On imports with an expansion valve the valve opens or closes to adjust the flow and usually keeps the temp around 50 degrees. Most of the imports I've converted would hold that 50 degrees even at an idle. My 06 titan with auto climate control will only blow 50 degrees out of the vents. I agree R12 does have the ability to get colder than 134 but it doesn't make a difference in a system with and expansion valve. I remember a Lincoln town car I worked on back in the early 90s, R12 with an orifice tube. In the shop idling on max recirculate with the blower on low speed it blew 17 degrees out of the vents. I never got a 134 system to blow that cold.

James

[krmiller07]

From my experiences that doesn't always hold true. In american vehicles with the orifice tube to regulate the flow it does because it's a set size. On imports with an expansion valve the valve opens or closes to adjust the flow and usually keeps the temp around 50 degrees. Most of the imports I've converted would hold that 50 degrees even at an idle. My 06 titan with auto climate control will only blow 50 degrees out of the vents. I agree R12 does have the ability to get colder than 134 but it doesn't make a difference in a system with and expansion valve. I remember a Lincoln town car I worked on back in the early 90s, R12 with an orifice tube. In the shop idling on max recirculate with the blower on low speed it blew 17 degrees out of the vents. I never got a 134 system to blow that cold.

James

 

 

Thanks James,

 

I actually took the truck to a mechanic yesterday, and he re-charged it. After finding it was about a 1/2 lb. low and discovering that the loose nut that did the convesion from R12 - R134a had left the (HI) side nipple loose. He recharged it. It's hard to say if it was a dramatic improvement, since the tempature up here went from 102 degrees on day to about 65 yesterday.

 

Another discovery worth mentioning is. After several trips to and many questions to different (Techs) he discovered 2 LARGE vacuum leaks that were coming from the vacuum lines off of the EGR and off of what looks like a line to the Cruise Control.(Comes up out of the REAR of the manifold). He used a smoke machine typically used to trace out leaks for an A/C system. Once we hokked up to a vacuum line and blew smoke in the throttles body and intake manifold, smoke poured out of the leaking lines like a toy train !

Truck idles and runs smoother than it ever has, and I'm hoping the MPG improves as well.

 

Now the best part...TOTAL COST was $55.00 including refridgerant! If this does the trick, than I'll have saved a pant load of $$$, not having to pull the intake manifold and replace the gaskets as previously diagnoised by EVERY tech I went too.

 

I'll keep you posted on my mileage results.

Edited June 12, 2011 by krmiller07

[JamesRich]

Thanks James,

 

I actually took the truck to a mechanic yesterday, and he re-charged it. After finding it was about a 1/2 lb. low and discovering that the loose nut that did the convesion from R12 - R134a had left the (HI) side nipple loose. He recharged it. It's hard to say if it was a dramatic improvement, since the tempature up here went from 102 degrees on day to about 65 yesterday.

 

Another discovery worth mentioning is. After several trips to and many questions to different (Techs) he discovered 2 LARGE vacuum leaks that were coming from the vacuum lines off of the EGR and off of what looks like a line to the Cruise Control.(Comes up out of the REAR of the manifold). He used a smoke machine typically used to trace out leaks for an A/C system. Once we hokked up to a vacuum line and blew smoke in the throttles body and intake manifold, smoke poured out of the leaking lines like a toy train !

Truck idles and runs smoother than it ever has, and I'm hoping the MPG improves as well.

 

Now the best part...TOTAL COST was $55.00 including refridgerant! If this does the trick, than I'll have saved a pant load of $$$, not having to pull the intake manifold and replace the gaskets as previously diagnoised by EVERY tech I went too.

 

I'll keep you posted on my mileage results.

Sounds like you found a good mechanic! Hope it solves you MPG problem too.

James

[ahardb0dy]

"Look at your sight glass on the drier right behind the grill"

 

Keep in mind you will only have the sight glass if the drier is an OEM part, aftermarket driers do not have them, (at least the few I have used on my sentra)

 

The proper way to add refrigerant is to do so by weight, the guy I use does it by reading the pressures, I have had no problems with his work. My sentra that he worked on for me, with an aftermarket compressor, new expansion valve and drier will cool into the 30's, (temp readings were taken with a digital tester and a regular old meat type thermometer at the vent) the PF does not cool as well, it goes into the 40's but it takes a while, but on the PF all he did was charge the system and I have no clue on how old the other parts are since I haven't replaced any of them yet.

 

I recently used coil cleaner from Home Depot to clean the condenser in my sentra and it seems to cool down faster

 

The expansion valve if faulty,clogged or just worn out will not regulate the freon flow and you will not get cold air no matter what you do.

 

It is possible to over pressurize the AC system and more is not better, once you add too much freon the system will not cool as well as if the proper amount is added.

[trogdor]

Some times it pay's to just take to someone. Glad you got it all sorted out. let us know if it does help you MPG.

[krmiller07]

The mileage has doubled from 8 mpg to 16 mpg in 'city' driving. The A/C is still acting up though. Compessor cycles on and off every 30 seconds or so.

Checked and added refridgerant with a set of gauges and an outdoor temp of about 65 dgrees. System was about a 1/2 lb low according to the gauges.

 

Any more ideas? I've been going through the FSM James Rich sent me : ). Thanks James!

 

Thinking about having the entire system evacuated and recharged?

 

Thanks,

 

KM

Edited June 19, 2011 by krmiller07

[adamzan]

The mileage has doubled from 8 mpg to 16 mpg in 'city' driving. The A/C is still acting up though. Compessor cycles on and off every 30 seconds or so.

Checked and added refridgerant with a set of gauges and an outdoor temp of about 65 dgrees. System was about a 1/2 lb low according to the gauges.

 

Any more ideas? I've been going through the FSM James Rich sent me : ). Thanks James!

 

Thinking about having the entire system evacuated and recharged?

 

Thanks,

 

KM

I would have it evacuated and see if it holds a vacuum if not you have a leak somewhere. My 95SE has its factory a/c still working at it is nice and cold. I got it from the original owner. My XE on the other hand I had to replace all the o-rings to stop it from leaking.

[JamesRich]

The mileage has doubled from 8 mpg to 16 mpg in 'city' driving. The A/C is still acting up though. Compessor cycles on and off every 30 seconds or so.

Checked and added refridgerant with a set of gauges and an outdoor temp of about 65 dgrees. System was about a 1/2 lb low according to the gauges.

 

Any more ideas? I've been going through the FSM James Rich sent me : ). Thanks James!

 

Thinking about having the entire system evacuated and recharged?

 

Thanks,

 

KM

what were your pressures at with the gauge set? If your high pressure is up around 200 or higher and your low below 20 to 25 at 65* your expansion valve could be stuck. When checking pressure with gauges always run the blower on high with the door open and not on recirculate. The colder it gets inside the vehicle the lower the pressure will get.

You could check for leaks with soap and water over the connections you can see but it could leak somewhere you cant reach. I never found a leak detector that worked worth a crap. The die works pretty well to find leaks but it has oil in it so you are adding more oil to your system.

James