I Got The Air Conditioner Blues

Back in the day, when tube transmitters ruled the broadcast world, common practice was to have a big cooling fan moving outside air through the transmitter building connected to a thermostat.  Temperature swings of 30 to 40 degrees were common, however, the tube rigs could handle almost any temperature that didn’t melt plastic or freeze water.

Today’s solid state transmitters are not that rugged.  They like to have there rooms around 70 degrees +/- 10 degrees or so.  Not to mention the other computer controlled equipment commonly found at a transmitter site.  Things like air chain processors, STLs, remote controls, etc.  So, lots of air conditioning is the norm, and with lots of air conditioning comes lots of maintenance.

Air handler air filters need to be checked and replaced often.  Condenser coils seem to attract every type of flying debris on the planet and need to be cleaned once, possible twice per year depending on tree and weed species near the site.  Even with the preventative maintenance, occasionally things like this happen:

AC condenser frozen dryer and piping
AC condenser frozen dryer and piping

Of course, the entire cooling coil inside is frozen solid.

This condenser is low on refrigerant, causing icing problems.  It has a slow leak somewhere and is about to be replaced.  Other reasons for this happening are malfunctioning or non-existent low ambient kit on the condenser fan.  Sometimes less than knowledgeable persons will install a 5 ton unit designed to run throughout the year but not take into account the effect of moving below freezing air at high speed across the coils.  Insufficient air moving across the cooling coil will also cause this.  Insufficient air flow can be due to plugged air filters or clogged fan/blower blades.

This one is even better (same condenser unit):

AC condenser broken fan
AC condenser broken fan

The fan blade is sheared off and jammed into the condenser coil.  This happened during power transfer from generator power to commercial power.  Naturally, it was at 1 am in the morning after a pole mounted transformer had been replaced.  When the building transfered back to commercial power, I went outside to use the “bathroom” before my two hour drive back home.  I though I smelled something hot, you know that cooked paint/plastic smell, but couldn’t really track it down… the winds were kicking up and another thunderstorm was on the way.

The next afternoon, however, when the sun was up and the site was working on one air conditioner, the temperature alarm went off.  Upon arrival, I found the condenser breaker tripped, resetting it caused the building lights to dim.  The fan motor was shorted to case.  I would theorize the aluminum fan blade suffered from metal fatigue, likely because the blades were not balanced causing a vibration.  When the power transfer occurred, there was just the right combination of torque and centripetal force to cause the blade to rip, then lodge in the condenser coil.

The fan motor has replaced, but I think it is time to replace the whole condenser unit, which will be expensive.

AC&R Gauge set
AC&R Gauge set

I found having a set of gauges to check the head pressure and suction is a good diagnostic tool to quickly pinpoint problems with HVAC units.  This way, when the HVAC tech shows up, you can quickly point him in the right direction.

The breaker keeps tripping…

This is yet another addition of the “Burned up Sh*t” collection:

GE 30 Amp 3 pole breaker
GE 30 Amp 3 pole breaker

It is a breaker from a 5 ton AC compressor.  Back in the bad old days when I was the Director of Engineering for a 28 station group Headquartered in Harrisburg, PA, I received a phone call from one of the local engineers.  He stated that the studio AC unit compressor had burned out again and the breaker keeps tripping.  What did I think, asked he.  I thought perhaps he should dig a little deeper and determine why the breaker was tripping before throwing another AC compressor at it.  When are you coming to town again, he cheerfully inquired.

Okay, I get it.

I started by calling the HVAC company to inquire what had gone wrong with the compressors.  Winding shorted to case for both units was the answer received.  It being July and mighty hot out, the various worker bees in the studio where feeling inconvenienced by the sweat in their eyes and dripping on their work, etc.  I called the local manager and asked for a hotel room, I’d be up tomorrow.  Then I called the HVAC guy back and asked in to meet me at the studio tomorrow afternoon.

Upon arrival the next morning, I found the fifth floor studios to be hot, as reported.  I trip to the roof location proved to be hotter still.  I tested the voltages at the compressor unit with a DVM and everything looked good.  A trip down to the utility room found the electrical panel in reasonable shape.  Then the local engineering guy chimed in, “Oh yeah, I forgot to tell you, the breaker hums and gets hot when the compressor is on.”

It’s always that little bit of missing information…

I took the breaker out and sure enough, the fingers were all arched and nasty looking.

I replaced the breaker, the HVAC guy showed up, with a new compressor and the studios began to cool off around 3 pm.

Since then, I specify Square D QO bolt on breakers for new installations, especially for heavy loads like AC units, transmitters, and so on. They are a little more expensive, but in the light two AC compressors, the unscheduled trip out of town, and the grumbling staff, it is better to pay upfront for better equipment than to put up with preventable outages.

Cracked Battery Terminal

File under some new everyday. Yesterday, there was an area wide power outage in Woodstock, NY. The backup generator failed to start, however, WDST remained on the air until the UPS batteries ran out several hours later.  Then my cellphone rang.  Alas, yet another Sunday on the job.

Upon arrival, I found the power had just come back on, so the DJ (yes, there was a live person in the studio, on Sunday) was restarting the NextGen system and getting the station back on the air.  I restarted the rest of the servers, streaming computers and what not.  While I was there, I figured I might as well see why the generator didn’t run.

Pressing the start switch led to the “click, click, click, click…” which normally indicates the battery is dead.  Deciding that I should dig a little deeper, I got the volt meter out.  Battery voltage, no load 13.8 volts.  A normal reading.  Flick the starter switch and measure the battery voltage again, under load 13.7 volts.  Hmmmm, now that is not what I suspected.  If the battery were bad, the voltage should drop down under load.

Cracked Battery Terminal
Cracked Battery Terminal

I grabbed the negative cable and it came off in my hand.  Another one of those “ah ha!” moments.  Upon closer examination, the terminal connector is cracked in half.

Cracked Battery Terminal
Cracked Battery Terminal

I went to the local Ford dealership and bought a heavy duty truck battery cable.  Since the battery itself is six years old, I decided to bring it and have it checked, and sure enough, the battery was going bad too.  Rather than suffer through another power outage without generator, I went ahead and replaced the battery.

Why the terminal cracked in half in the first place, I don’t know.  Perhaps it was over tightened, or some type of manufacturing defect.

Care and feeding of Propane Fueled Generators

Broadcasters historically have tried to remain on the air during emergency events like major storms, earthquakes and other forces of nature.  Often times, commercial power is interrupted, and thus, the backup power generator is installed.  Propane powered generators for medium duty (powers up to 45 KW) are popular because of the decreased environmental hazards, availability and expense of fuel, ease of maintenance and repair.  This sized generator can run the critical loads of a studio facility or a transmitter site with TPO’s between 5 and 10 KW.

Katolight 45 KW generator w/outside housing
Katolight 45 KW generator w/outside housing

Most propane generators use a gasoline engine modified to use propane.  These generators can also use natural gas, however, because natural gas has slightly less energy, the generator’s service rating is reduced by about 10 percent.

Ford inline 6 cylinder engine
Ford inline 6 cylinder engine

The biggest error I consistently see with propane generators is improper fuel tank sizing.  It might seem just fine to plop a 500 gallon tank down next to a 45 KW generator and expect everything to be just fine.  500 Gallons may sound like a lot of fuel, but the more important consideration is tank vaporization, that is to say, how fast can the liquid propane can be removed from the tank for use.  Propane fuel companies should be able to sizing these things correctly, most of them have books and charts that tell what capacities and sizes are needed.  However, as a general trouble shoot guide, the following information is provided:

Generator manufactures will specify how many BTU per hour a generator will require under full load. If not, these are some conservative rules of thumb:

  • For every 1 KW of electrical generation, 2 horsepower of engine is needed*
  • Under full load, each horsepower will consume 10,000 BTU per hour*
  • Propane has 92,000 BTU per gallon
  • Propane weighs 4.2 pounds per gallon

*Note: These are not the figures you will find in your engineering handbooks, they are adjusted for generator winding and engine efficiency.

Propane Tank Vaporization Rates (Continuous BTU/hr vs volume at tank temperature):

Size propane in a tank (assumes 1/3 full) Maximum continuous BTU/hr at degrees F
20° 40° 60° 70°
120 129,600 188,640 247,680 308,160 338,400
150 146,880 213,790 280,700 349,200 383,520
250 253,800 369,400 485,000 603,480 662,700
325 321,300 467,670 614,000 763,900 838,900
500 396,270 567,700 757,300 942,240 1,034,700
1000 708,480 1,031,230 1,353,980 1,684,600 1,849,900
1450 816,120 1,253,400 1,645,690 2,047,550 2,248,480

Note: Tank vaporization depends on fuel level, tank temperature and withdrawal rate.  The above chart is a conservative generalization and represents a safe median value.

If a propane tank cannot vaporize fuel fast enough, the generator will begin to run lean, eventually overheat and shutdown. The vaporization rate depends on the tank temperature, which drops as fuel is withdrawn.  For the above cited 45 KW generator called to duty after a sever winter storm, the tank would need to vaporize: 45KW x 2 HP = 90 HP.  90 HP x 10,000 BTU/hr = 900,000 btu/hr.  A 500 gallon tank is too small for that size generator.

As the tank temperature drops a propane tank can develop frost on the outside of the tank, even on a hot summer day, which compounds the problem.

The correct size tank for a 45 KW generator is a 1000 gallons.  This can also be two five hundred gallon tanks connected in parallel via a high pressure line.

45 KW propane generator with two 500 gallon tanks
45 KW propane generator with two 500 gallon tanks

Also note, the generator’s radiator is facing the tanks so that when the unit is running, hot air is blowing on the tanks, warming them up.  This particular generator is about 25 years old, which is why it looks a little worn.  It still carries the load and mechanically is in sound condition.

Most propane fuel systems have two regulators; one high pressure regulator on the tank, which takes the variable tank pressure and steps it down to about 10 PSI, and the vaporizor which steps the pressure down to a few ounces per square inch (or inches water column) and adds air creating propane gas for the generator to burn.

High pressure propane tank regulator
High pressure propane tank regulator

It is important that the vaporizer be mounted above the snow line and that there is a little screen on the air intake, otherwise mud wasps will build a nest in the air intake and the next time the generator is required to run, it won’t start.

Low pressure propane regulator/vaporizer
Low pressure propane regulator/vaporizer

Fuel piping is also a concern, if the low pressure lines are not large enough to handle the required BTU, the generator will run lean, creating the same problems of an improperly sized tank.  Different piping has different capacities, see the following charts:

Propane steel pipe sizing diagram
Propane Schedule 40 steel pipe sizing diagram
Propane copper pipe sizing diagram
Propane copper-K pipe sizing diagram

Assumes pressure less than 1.5 PSI, one MBTU is equal to 1,000 BTU per hour.

Once the generator is installed, maintenance is required.  As a minimum:

  • Exercise engine bi weekly for 15 minutes. Propane generators do not need to run under load.
  • Check fuel, oil, and antifreeze levels monthly, more often if heavy use.
  • Change the oil, oil filter, air filter, check antifreeze freeze point, battery electrolyte specific gravity yearly
  • Change out belts and hoses as needed, pay close attention to the block heater hose, this is where leaks often develop
  • Clean out mice nests and droppings as needed

Mice love generators.