How to troubleshoot and repair an HPF error on Marine Air Conditioner

If you have a boat with air conditioner or heaters, you have likely seen the dreaded HPF error (High-Pressure Freon or High-Pressure Fault) error. Depending on the manufacturer or your air conditioner, it may be a numeric error code, or in our case it just displays HPF.

If this is happening during a cooling cycle, it is likely because of lack of water flow. If it is going on during a heating cycle, it is probably due to lack of air flow. In our case, it was through a cooling cycle.

We were not getting any water discharge out of the unit on the side of the boat. I started by checking the water filter in the water circulation line doubting it would be this simple or clogged that much. The filter was all right so it was time to go on to more diagnosis.

My first step was to see if the motor was running. I put my hand on the motor and turning on the unit to see if I could feel the motor kicking on. I could not so I thought maybe the motor was shot. I removed the hoses from the motor and disconnected where the motor connects to the control board for the air conditioner. Ours is a Marine Airr but they are all pretty much the same components so you can likely follow these steps regardless of make.

I removed the motor from the bilge and did a bench test by just applying 110 volts directly to the motor leads. She fired up just fine. To see if I had some internal problems with the pump, I connected it to a bucket of water and validated that it was pumping water just fine.

While I had it out, I decided to clean the inside and outside of the motor water routes. This was rewarding, just because it had so much gunk in it and looked so clean when I finsihed.

Since the motor was working, I thought that maybe I had a control board problem. I used my multimeter to check voltage on the output for the pump motor. I turned on the unit, and the leads went to 110 volts for about 1 second then I got the HPF error again. The good news is that the circuit board was sending voltage to the motor. The bad news is I was not sure what was causing the HPF error.

I broke down and called Dometic (The company that now owns Marine Airrr) and spoke to someone in tech support. They told me that I could test the actual HPF switch by disconnecting it from the circuit board and essentially shorting the two leads on the board. The jumper tells the board that the HPF switch is essentially open (not in fault mode) and I would be able to see if the pump then runs.
He went on to tell me that if it runs with the HPF Switch jumpered than the issue is with the switch itself if it still doesn’t run with it jumpered then the problem is likely the actual main circuit board. The good news is that they still sell these. In the Southern United States, this is a company called AER out of Seabrook, TX.

I disconnected the HPF switch from the motherboard and jumpered the pins. I turned on the unit, and the compressor ran fine with no issue. I only ran it for a few minutes since the pump was still not connected. The good news is that I now know what the issue is. It is the HPF switch. I have one on order and will need to have someone put it on for me just because the freon will have to be charged after I do this.

With the issue known, now it is just time to put it all back together.

In the video this week (Below) I also recorded a storm rolling in over the time lapse camera on deck. I thought it was pretty cool. I hope you enjoy it too.


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