A/C problems

[imported_]

Good morning, I sure hope that someone has some answers for me. The A/C in my wife's truck is acting up. She does a lot of stop and go driving and it will blow cold under hard acceleration, such as leaving a stop light, but when she is idling or the engine speed is low the air is not cold. We just had a low pressure swith replaced and I replaced the serpentine belt and tensioner. The system showed no leaks and got down to 45 degrees before it left the shop. This only seems to happen during the hottest part of the day. Her truck is a 95 K2500 Suburban(5.7L). Any help would be appreciated. Thank you.

Paul

[HowieE]

Open the hood turn the AC on and off and make sure the clutch ingages a idle. If it does ingage and turns the shaft then watch the clutch as you rev the engine from idle to 1500 rpm and back down to idle. Does the clutch rpm follow the engine rpm? If the clutch did not track the engine you may have a week clutch.
If the clutch seamed to act right I would put a set of guages on the system and look at the suction pressure at low rpm compared to suction line temperature. If the suction line feels warm, close to the compressor, you have lost a valve in the compressor.

[Truenorth]

Is the air set for fresh exterior air in the cab or recirculation. Once the air as slightly cooled down in the cab I would recommend setting to recirculate the air in the cab rather than pulling warmer (90f+ air) from outside and trying to cool it. I know with the new refrigerants (134a) they do not cool as well at idle as the good old R12.

[oldmansax]

HowieE is on the right track here but I would caution anyone who has A/C problems to find a knowledgeable HVAC mechanic (not necessarily your favorite auto mechanic)and have him check the system out. Refrigeration is a discipline unto itself & there are many factors that can influence cooling capacity. A system that was designed for R-134A should be more efficient than the old R-12 systems (see excerpt from Dupont below); however due to

[Truenorth]

Being a ex commercial refigeration mech, I seen people/start tearing apart a/c systems looking for a problem rather than looking at the obvious. Having worked with a range of refrigerants I do agree that MP-39 is much more efficient than it's counterpart 134a or R12. Seemingly 134a at idle in a vehicle does not seem to attain the same level of cooling as R12. When moving at highway speeds it seems to be much better. In extreme heat recirculating interior air at idle will improve cooling(considering your system is functioing properly). Finding a trusting A/C mechanic is the key...as previously stated.

[imported_]

Thanks for the help guys. When I start the truck the compressor clutch turns on and off continuously. It will turn on for about 20 seconds and then turn off and so on. We always keep the setting on recirculated air also. When looking for a good HVAC mechanic are there any special credentials to look for? Thanks.

Paul

[oldmansax]

Truenorth is right. The gain referenced is in efficiency and not performance. Also, loss of performance will be more evident at idle as soon as the compressor wears any at all. As to what credentials to look for I am at a loss. In almost 20 years as an HVACR contractor, I have hired guys with more credentials then I could hang on the wall, only to find out they did not have a grasp of refrigeration OR A/C. I have also hired guys fresh out of school who made excellent technicians. I would start with certifications. But also look at his tools, are they CLEAN? He should have a separate sets of gauges for R-12 & R-134A. Electronic scales, digital thermometers... he should spent some time assessing the system before he just dumps in some refrigerant & says

[patrick m.]

o.k, if compressor cycles on and off, that generally means the refrigerant is low.
That means there must be a leak, dont let a national "chain" store tell you that you need a compressor, oriffice, Accumulator, and a system flush to the tune of $1100. That seems to be the norm around here.
I own a repair facility, and get many a/c repairs a month because these profit mongers are selling things people dont need.
(maybe i cant spell, but i know the difference between right and wrong :D )

[HowieE]

If the compressor cycles while there is a load on the system, cabin temperature above the set point, you are low on gas.
Leaks in an automotive system are realy hard to find. Often you find them by mistake rather than the use of a leak detecter and often when the system is cold rather than operating. I have see the piping just at the compressor crack or leak past the O rings that seat the manifold to the compressor. Neither showed up while the system was hot, but could be seen with soap while the system was cold and light pressure placed on the piping.

[charliepeterson]

If the vehicle doesn't have the leak die in it than I would put it in. "The die doesn't lie" One other thing the life expectancy of the components in the automotive A/C system is only five years.
With the new 134A systems the charge capacity is critical. More is not better and even one pound down can ice up the evaporator. Air in the system will kill it.
Converted systems from R12 to 134A can and do very well with 80% of the original charge weight. If converted though it could be a yearly thing to evacuate,vacuum and recharge only because of the design of the hoses, no inside barrier.

[carco]

Paul, if system is cycling as much as I think you are indicateing, it is low on charge. Yes, find a qualified HVAC tech, preferably not a chain store, they push parts sales partly due to high rent real estate locations and high 12-25 percent fees paid to the franchiser. Yes, add flouresent dye to the system this will help future leak detection, $10-20. Yes, use only R12 or R134a freons. Other freon requires equipment 99% of shops will not have so if out of town most shops can not legally repair your HVAC system, unless you find that one shop with the dedicated equip to a particular freon. One piece reclaimation/ recycling equipment does one freon only, $2500 to 3500 per machine. Stay R12 if possible but if replaceing compressor try switching to R134a since drier also needs switched w/ compressor and replace as many o-rings as possible as well as worn hoses as needed. Use of a good $250. plus, electronic detector will find 90% of the leaks, by a good tech! Dye will find rest. hth bob

[Truenorth]

For those iterested, this is a product that could potentially save you $$$ on your A/C systems. I have not tried this product myself, but I am seriously looking into it as an alternative for central air repairs for friends.


www.duracool.com (http://www.duracool.com)

[Cowracer]

I know guys who swear that you can use propane as a replacement for r-12 (not in MY truck, buddy)

This DURACOOL sure sounds like propane or a propane-like substance. Anyone ever seen what happens to a diesel that starts breathing propane? Loud, messy and expensive.

I'll pass on the duracool

Tim

[whatnot]

I have been using Envirosafe in a lot of vehicles and it works very good. It has bigger molecules and won't leak out where R134-a will an and it cools better. It will also work with either kind of oil and doesen't require a vacuum on the system first.
Another reason to use it that you can't buy r134a in Wisconsin. Envirosafe website (http://www.es-refrigerants.com)