Cool School
Q: I bought an '86 GMC shortbed pickup with marginal air conditioning. It does blow air, but it isn't very cold, so I'm pretty sure the refrigerant is either gone or else very low. Right now I'm more concerned about heat than cooling, but summer will be here soon and I would like the A/C to work well. It gets pretty warm in Missouri during the summer.

My questions concern what is the best way to refurbish or repair the air conditioning. Can I still use the old R-12 refrigerant, or must I use the new R-134a? Can I do some or all of the work myself? Does the new refrigerant work as well as the old stuff? When I'm recharging the system, is there anything else I can do to optimize the air conditioning. I hope you can give me some cool advice.
Jeremy Jonstadt, Springfield, MO

A: "It depends" is the best way to summarize your questions. The answers depend on many things, including local regulations, supplies of R-12 refrigerant, and how good or bad your definition of marginal is.

You need a baseline analysis of your current system. A repair shop that is certified to do air conditioning work should be your first stop. The shop can evaluate your truck and explain your options.

If your current system is simply low on refrigerant, but otherwise in good working order, you're probably fine sticking with R-12. Air conditioning systems that were designed to work with R-12 obviously work best with R-12.

R-12 was replaced with the more environmentally friendly R-134a in 1996, but R-12 systems were allowed to be recharged with new R-12 as long as supplies lasted. Prices shot up and there was some hoarding, but as prices increased, more R-12 seemed to find its way out of the woodwork. Your local air-conditioning expert can tell you about current prices and supplies.

Converting an R-12 system to R-134a typically reduces performance by approximately 5 to 15 percent. The percentage depends on the efficiency of your condenser. This performance drop will still seem like an improvement compared with a truly marginal R-12 system.

If your current air-conditioning system needs any of the major components replaced, such as the compressor, condenser, or evaporator, it makes much more sense to update the system to R-134a. The ease and cost of the conversion is related to the age of the vehicle and the current components it has. Systems that already have barrier-style hoses and R-134a-compatible seals are much easier to convert.

Federal laws state that new R-134a fittings must be used on the high and low service ports. That's to prevent anyone from trying to recharge an R-134a system with the old R-12 refrigerant. To help avoid this problem, warning labels are supposed to be installed on retrofitted A/C systems.

It's not a good idea to mix types of refrigerants. Doing so will seriously affect the performance of the system by increasing operating pressures. Excessive pressures can overstress the compressor to a point of failure. R-134a compressors can also fail from the use of incompatible lubricants.

You should have air-conditioning servicing done by a professional shop. A prime reason for letting the pros do the work is that they have the specialized equipment necessary to safely evacuate the old refrigerant. People who just let the old refrigerant escape into the atmosphere are harming the environment.

A typical retrofit conversion includes evacuating the old refrigerant, replacing the accumulator with an X-7 desiccant unit, installing new O-rings, installing a new high-pressure cutout switch, changing the orifice tube, adding PAG oil, and recharging the system with new R-134a refrigerant. Once your truck has been converted, it will be easy to have it recharged if necessary.

There is some capacity loss when an old system is retrofitted to R-134a, but there are ways to regain some of that loss. There are aftermarket orifice tubes with a variable valve (instead of the old fixed tubes). Variable tubes change the flow rate for improved low speed and idling A/C performance. Lowering the outlet air temperature with a variable valve can reduce temperatures by 5 or 6 degrees.

A larger, more efficient condenser is a good idea when going to an R-134a system. Whenever an old condenser or evaporator needs replacing, be sure the new unit has a BTU rating as high or preferably higher than the original unit.

If you decide to stick with your current R-12 system, consider adding an auxiliary cooling fan. A separate electric fan for the air-conditioning condenser will improve A/C performance at idle and when crawling along in traffic. By dissipating excess heat, the air-conditioning system doesn't have to work as hard.

Shaft City
Q: There's a ringing noise that won't go away in my '94 Dodge Ram pickup. I don't abuse the truck, but I don't baby it, either. The noise is loud enough that several friends have commented on it. It sounds like the noise is more underneath the truck and toward the back rather than coming from the front of the truck or the engine compartment.

The sound is definitely a ringing, metallic sound as opposed to a grinding or thumping sound. I've crawled around underneath the truck several times looking for loose parts. I've tightened all the fasteners I could see and didn't find anything overly loose. Do you know of any ringing noise problems specific to my truck, or can you suggest any areas to check out? Thanks for your help
Ben Lewis, Pocatello, ID

A: Troubleshooting noises are difficult in person, much less by letter. Driveshaft problems can produce ringing noises. Similar ringing noises have been encountered on a number of '94 and '95 Dodge Ram pickups, so Dodge released an improved driveshaft. The new unit is insulated. It's listed under part number 52105260.

Another noise problem related to '94 and '95 Ram trucks is a frontend rattle or clunking sound. If you encounter that noise, check out the antisway bar links where they attach to the antisway bar.