Garage Heater Placement, a Gardner Denver Air Dryer, and Why the Compressor Catalogue Wasn't Enough
A heater I almost missed
In January 2025, a customer called about a Gardner Denver air dryer that kept tripping on high refrigerant pressure. The service technician told me he would put money on a bad condenser. I said that was plausible. We were both wrong.
I review air compressor installations before customers accept them. It is not a glamorous job, but I see patterns. In our Q1 2024 quality audit, we rejected about 7 percent of first deliveries for problems that should have been prevented: undersized drains, poor ventilation, and the occasional bypassed dryer. This customer's installation was not rejected at the first review. The mistake showed up later, and it was hiding in plain sight behind a garage heater.
The customer ran a maintenance garage. They found a 20 hp package in the Gardner Denver compressor catalogue and ordered a refrigerated air dryer plus filtration and a receiver. The selection was solid. Then the shop got cold, and someone bought a forced-air garage heater. That is a reasonable thing to do in an unheated building. The issue was not the heater itself; it was where they mounted it.
What the site visit showed
The first technician checked everything you normally check before you declare a condenser bad. The condenser coil was clean. The fan spun freely and pulled the expected amperage. Refrigerant charge looked right. High side pressure, however, was too high, and the dryer kept cutting out after about twenty minutes.
Then the garage heater cycled on while he was taking readings. He told me to come stand beside the dryer. The air blowing into the condenser felt like a hair dryer. When he put a temperature probe at the condenser inlet, it read 114F. The rest of the shop was cold. That is the whole diagnosis, once you believe that the condenser matters as much as the compressor.
The catalogue clearance was technically met. There was enough space to walk around the package. But clearance for access and clearance for heat rejection are not the same. The compressor was fine. The dryer was fine. The installation was the problem.
What is a condenser?
The customer's lead mechanic asked me a genuinely good question: what is a condenser? I get that more often than people expect. A condenser is not a water separator. It is part of the sealed refrigeration circuit inside a refrigerated air dryer. It is the finned coil that releases heat from hot refrigerant gas, which condenses it into liquid. The fan on the condenser is there to help that heat leave the cabinet.
That matters because a refrigerated air dryer works by removing heat from compressed air. If the condenser cannot reject heat, the cooling side of the dryer cannot stay cold enough to condense water vapor out of the air. A dirty or overheated condenser means wet air downstream even when every internal part is healthy.
When I went back through the Gardner Denver air dryer troubleshooting chart, it pointed to the same cause. High refrigerant pressure usually comes from restricted condenser airflow, a failed fan, high ambient temperature, or too much refrigerant. Only one of those applied. High ambient temperature is a relative thing. The shop was cold, but the dryer's condenser was living inside the warm jet of air from a large garage heater.
What the compressor catalogue could not show
Back at my desk, I opened the Gardner Denver compressor catalogue again. It had output numbers, pressure ratings, minimum ambient temperatures, and a note about ventilation. That catalogue did its job. What it cannot do is follow every added heater, fan, or wall that changes airflow at a specific job site.
I used to think equipment selection was the hard part. If the load matches the compressor and the dryer matches the load, the installation would run. I only believed that installation conditions deserve the same care as the equipment spec after I watched a 20 hp package fail to dry a maintenance shop because of one heater. That mistake is now part of my review process.
To be fair, a cold compressor room creates its own set of headaches. A garage heater is often the right answer in winter. It should heat the whole room, not point directly at the compressor intake or the dryer condenser. Good placement means enough distance, clean airflow, and a thermostat that keeps the space at or above the minimum operating ambient required by the equipment.
The repair and the real cost
We debated two ways to fix this. Option one was a deflector in front of the garage heater to steer the discharge away from the dryer. Option two was moving the heater to an outside wall and re-commissioning the air dryer. A deflector was cheaper and faster. The safer fix was moving the heater and verifying the pressures afterwards.
We went back and forth for longer than I care to admit. A deflector seemed good enough, but if the heater cycled on while no one was nearby, the risk came back. The customer needed dry compressed air every day. That tipped us toward the more certain solution, even though it cost more.
The first crew that bid on the move said they could probably get to it next week. Calling that probably was enough to eliminate them. We paid a little more for a smaller crew that committed to a fixed date. The difference was not speed for speed. It was certainty, and in an emergency that is worth a premium. The customer's own estimate for losing one day of work was much larger than the cost of the change order.
The checklist question I use now
I added a simple question to every pre-delivery review: is there a heater in the room, and where is its air stream going? In Q1 2025, that question caught two installations before equipment was placed. It is not in the compressor catalogue, but it should be in every site checklist.
I still kick myself for not asking about added heaters during the first project review. If I had, the customer could have avoided a service call and a rushed change order. But mistakes can buy you rules. This one bought us a rule that will probably pay for itself many times over.
If you are setting up an air compressor in a cold space, keep the space warm in a sensible way. Use a garage heater if you need one, but keep it away from the condenser and the compressor intake. And before you blame the dryer, check what is actually blowing on it. That one question would have saved us all a long afternoon.