How to diagnose high head pressures at the air conditioning or heat pump compressor:
What are the causes of high head pressure at an air conditioner or heat pump compressor motor?
This article lists twelve causes of high head pressure and explains their causes, effects, and diagnosis.
Some of these, such as a bad TXV or clogs in the refrigeration system are cited as the most common causes of high compressor head pressure.
This air conditioning repair article series discusses the the diagnosis and correction of abnormal air conditioner refrigerant line pressures as a means for evaluating the condition of the air conditioner compressor motor, which in turn, is a step in how we evaluate and correct lost or reduced air conditioner cooling capacity.
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Below we list a dozen causes of high head pressure in an air conditioner or heat pump compressor motor. Of these, debris clogging or malfunctioning TXVs seem to be the most common problems.
Note: air or water contamination in HVACR systems is common and can be introduced by a tech who does not purge air from gauge hoses before attaching the refrigerant gauge or by failure to evacuate the system when refrigerant has been lost and the system is to be repaired and re-charged. Installation of a filter/drier should also always be included in such repairs.
Experts note that the symptoms of air contamination and refrigerant overcharge can be similar. ACHR NEWS calls these "non-condensibles" in the refrigeration system.
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Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
Causes of abnormally high pressure on the "low side" in an HVAC system
What happen the low side very high pressure - On 2020-07-13 by Wilson phan
What causes high pressure on the suction line on Rheem R410a ? - On 2020-06-13 by Clay
Reply (mod) - high refrigerant pressure on the low side: TEV stuck open ?
Wilson and Clay:
When you have abnormally high refrigerant pressure on the low side or suction side I suspect a failed thermostatic expansion valve that is stuck "open" .But there are other causes of high low-side pressure as you will read above on this page.
I had a lennox system that had a very weird set of symptoms. It was an r22 3ton that was around 20 yrs old.
In the course of 10 days the system kept popping the high head pressure switch (8 times total) yet the temp difference between intake and output (inside) was only 6 degrees.
The AC tech from the home warranty co. blamed it all on a 20% damage area to the condenser from corrosion, and his test set was a clamp on amp meter.
He never once connected gauges to check high/low pressures.
10 days after first incident, the compressor locked up and gave up the ghost.
When the new system was being brought in, the installer noted the pressure in the system (both sides) was only at 100# and the ambient temp was 95 degrees (per the gauges), the installers claim that the old system did not have enough refrigerant, and that the TEV was clogged/jammed.
Does this sound right? Too little freon, clogged TEV, 6 degree drop from intake to output, and still pop high head pressure?
This question appeared originally at OVER CHARGED of REFRIGERANT, EFFECTS - Tim nordyke
Reply by (mod) - retired HVAC repair technician: maybe.
Maybe, Tim. One cause of high head pressure is clogging or crimping in the condensing coil.
Causes of high head pressure in an air conditioner or heat pump system
I guess the tech is seeing sometihng we don't or she was not an English major and is not a great communicator who didn't explain in more detail how the problem was traced to the coil. .
Perhaps the thought was that internal corrosion was causing the condensing coil, check valve, or a refrigerant metering device to clog, risking blowing a compressor?
I'm suspecting a clogging TEV or a clogging valve on the compressor itself.
Reader follow-up:
Well that's why I'm coming here.
The clueless tech only used an ammeter to check current draw, said that 6 degree drop from intake to out wasn't the best, but was not a solid indicator of a problem.
I learned last night that the system had to be recharged 7 years ago and all they did was add freon.
So I'm thinking that the prior problem contaminated the system, the freon was leaking out, the TEV was clogged so it couldn't shut off flow to the evap coil, and since the return line wasn't cold enough to cool the compressor, it overheated and locked up.
Had tech 1 hooked up his gauges when the system was still running he would have caught the pressure issue and saved my system.
Reply:
Maybe so Tim. I like to assume just one snafu at a time:
Certainly if they added freon and didn't fix the leak you'd be low on freon again.
Low freon can ice the coil reducing or stopping actual cooling and it might ice the TEV causing it to block all refrigerant flow.
That MIGHT give a high head pressure.
The problem would continue until so much refrigerant has been lost that the TEV no longer ices (and the coil no longer cools).
What does your service manager say about the repair?
Reader follow-up:
Tim Nordyke said:
The tech offers nothing......
He is sticking to his claim it is all the condensers fault.
When the system ran just before it gave up the ghost, there was no ice or even condensation on or around the TXV (found correct name).
What has me wondering is how did I get a high head pressure (faulty switch?) when the pressures were at 100 lbs. just before they evacuated the system, and the amb. temp. was 95 degrees.
Reply:
If there was debris or corrosion-produced crud in the system it may have been stirred or moved by the refrigerant evacuation and re-charge system, then causing a clog at a check valve, condensing coil, TXV or filter/drier.
If the tech was convinced that the blockage was at the condensing coil it would be reasonable to replace it.
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Or see REFRIGERANT HIGH HEAD PRESSURE DIAGNOSTIC FAQs - questions and answers posted originally on this page.
REFRIGERANT HIGH HEAD PRESSURE DIAGNOSIS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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